CA1323620C - Catalyst for purifying exhaust gas and method for production thereof - Google Patents
Catalyst for purifying exhaust gas and method for production thereofInfo
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- CA1323620C CA1323620C CA000556595A CA556595A CA1323620C CA 1323620 C CA1323620 C CA 1323620C CA 000556595 A CA000556595 A CA 000556595A CA 556595 A CA556595 A CA 556595A CA 1323620 C CA1323620 C CA 1323620C
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- alumina
- rhodium
- catalyst
- platinum
- inorganic oxide
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Abstract
ABSTRACT OF THE DISCLOSURE
A catalyst for purifying exhaust gas comprises a honeycomb carrier of monolithic structure and a coating layer deposited on the honeycomb carrier and formed with a catalyst composition containing a refractory inorganic oxide in the form of particles possessing average particle diamter in the range of 0.5 to 20 microns, which refractory inorganic oxide has platinum rhodium deposited thereon in high concentrations. This catalyst is produced by coating the honeycomb carrier with an aqueous slurry containing the catalyst composition and calcining the coated carrier.
A catalyst for purifying exhaust gas comprises a honeycomb carrier of monolithic structure and a coating layer deposited on the honeycomb carrier and formed with a catalyst composition containing a refractory inorganic oxide in the form of particles possessing average particle diamter in the range of 0.5 to 20 microns, which refractory inorganic oxide has platinum rhodium deposited thereon in high concentrations. This catalyst is produced by coating the honeycomb carrier with an aqueous slurry containing the catalyst composition and calcining the coated carrier.
Description
CATALYST FOR PURIFYING EXHAUST GAS
AND METHOD FOR PRODUCTION THEREOF
BACKGROUND OF THE INVENTION
Field of the Invention:
; 5 This invention relates to a catalyst for - purifying exhaust gas. More particularly, it relates to a catalyst for purifying the exhaust gas from the internal combustion engine such as of an automobile for simultaneous removal from the exhaust gas of noxious 10 components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx), which catalyst - especially exhibits outstanding durability even when it is used under harsh conditions such as under a high-temperature oxidative atmosphere and manifests a 15 high purifying ability to the aforementioned noxious components at low temperatures.
Description of the Prior Art:
In conventional noble metal-containing catalysts for purifying the exhaust gas, for the purpose 20 of ensuring effective use of the noble metal contained in a very minute amount in the catalyst, efforts have been made to allow the noble metal to be deposited in as high a degree of dispersion as possible on a refractory inorganic oxide of a large surface area such as 25 activated alumina. ~he catalyst having the noble metal carried in a high degree of dispersion enjoys a high initial activity. When it is exposed to such harsh conditions as involved under a high-temperature oxidative atmosphere, however, the noble metal gains 30 gradually in particle size, undergoes a chemical conversion into a less active state, and tends to induce a reaction with the carrier substance and cerium oxide.
Because the noble metal is deposited in the high degree of dispersion, there tends to ensue a disadvantage that 35 the degradation of catalytic activity is rather heavy.
'' , , .
': ' , As carrier substances incapable of interacting noble metals, particularly rhodium, zirconia (U.S.P. No.
4,233,189) and alpha alumina (U.S.P. No. 4,172,047) have been known in the art. Zirconia and alpha alumina generally possess small surface areas. It has been pointed out, however, that the catalysts having rhodium carried on these substances have a disadvantage that exhibit poor - initial activity and possess no satisfactorily high ability to purify the exhaust gas at low temperatures after long term using.
An object of an aspect of this invention, -` therefore, is to provide a novel catalyst for purifying the - exhaust gas and a method for the production thereof.
An object of an aspect of this invention is to provide a catalyst for purifying the exhaust gas which exhibits outstanding durability even when it is used under harsh conditions and possesses a notable ability to purify thoroughly the exhaust gas of the noxious components thereof even at low temperatures and a method for the production thereof.
SUMMARY OF THE INVENTION
Various aspects of the invention are as follows:
A catalyst for purifying exhaust gas comprising a honeycomb carrier of monolithic structure and a coating ` 25 layer applied on said honeycomb carrier and formed with a catalyst composition comprising (i) a platinum group metal-supporting zirconia produced by depositinq said platinum group metal on zirconia powder, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and ` palladium, and (d) combination of rhodium, platinum and palladium, and is deposited in proportion in the range of 0.5 to 30% by weight on said zirconia powder.
A method for the production of a catalyst for purifying exhaust gas, which comprises coating a honeycomb .
AND METHOD FOR PRODUCTION THEREOF
BACKGROUND OF THE INVENTION
Field of the Invention:
; 5 This invention relates to a catalyst for - purifying exhaust gas. More particularly, it relates to a catalyst for purifying the exhaust gas from the internal combustion engine such as of an automobile for simultaneous removal from the exhaust gas of noxious 10 components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx), which catalyst - especially exhibits outstanding durability even when it is used under harsh conditions such as under a high-temperature oxidative atmosphere and manifests a 15 high purifying ability to the aforementioned noxious components at low temperatures.
Description of the Prior Art:
In conventional noble metal-containing catalysts for purifying the exhaust gas, for the purpose 20 of ensuring effective use of the noble metal contained in a very minute amount in the catalyst, efforts have been made to allow the noble metal to be deposited in as high a degree of dispersion as possible on a refractory inorganic oxide of a large surface area such as 25 activated alumina. ~he catalyst having the noble metal carried in a high degree of dispersion enjoys a high initial activity. When it is exposed to such harsh conditions as involved under a high-temperature oxidative atmosphere, however, the noble metal gains 30 gradually in particle size, undergoes a chemical conversion into a less active state, and tends to induce a reaction with the carrier substance and cerium oxide.
Because the noble metal is deposited in the high degree of dispersion, there tends to ensue a disadvantage that 35 the degradation of catalytic activity is rather heavy.
'' , , .
': ' , As carrier substances incapable of interacting noble metals, particularly rhodium, zirconia (U.S.P. No.
4,233,189) and alpha alumina (U.S.P. No. 4,172,047) have been known in the art. Zirconia and alpha alumina generally possess small surface areas. It has been pointed out, however, that the catalysts having rhodium carried on these substances have a disadvantage that exhibit poor - initial activity and possess no satisfactorily high ability to purify the exhaust gas at low temperatures after long term using.
An object of an aspect of this invention, -` therefore, is to provide a novel catalyst for purifying the - exhaust gas and a method for the production thereof.
An object of an aspect of this invention is to provide a catalyst for purifying the exhaust gas which exhibits outstanding durability even when it is used under harsh conditions and possesses a notable ability to purify thoroughly the exhaust gas of the noxious components thereof even at low temperatures and a method for the production thereof.
SUMMARY OF THE INVENTION
Various aspects of the invention are as follows:
A catalyst for purifying exhaust gas comprising a honeycomb carrier of monolithic structure and a coating ` 25 layer applied on said honeycomb carrier and formed with a catalyst composition comprising (i) a platinum group metal-supporting zirconia produced by depositinq said platinum group metal on zirconia powder, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and ` palladium, and (d) combination of rhodium, platinum and palladium, and is deposited in proportion in the range of 0.5 to 30% by weight on said zirconia powder.
A method for the production of a catalyst for purifying exhaust gas, which comprises coating a honeycomb .
- 2 -L~
... ..
` 1 323620 carrier of monolithic structure with an aqueous slurry containing (i) a platinum group metal-carrying zirconia, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide and calcining the resultant coating carrier, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and palladium, and (d) combination of rhodium, platinum and palladium and is deposited in a proportion in the range of 0. 5 to 30~ by weight on said æirconia powder.
A catalyst for purifying exhaust gas, consisting essentially of a honeycomb carrier of monolithic structure and a coating layer applied on said honeycomb carrier formed by a catalyst composition consisting of a first refractory inorganic oxide, free of noble metal or rhodium deposited thereon, and at least one second inorganic oxide of the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to ~ 20 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and (b) a refractory inorganic oxide having 1 to 20% by weight of : rhodium deposited thereon, and (B) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and 1 to 20% by weight of rhodium, said second inorganic oxide being in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns and being dispersed in the said coating layer, and (C) cerium oxide, free of noble metal or rhodium deposited thereon, and provided that where a member of group (C) is selected as a second inorganic oxide, at least one group (A) member or at least one group (B) member also must be present wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
... ..
` 1 323620 carrier of monolithic structure with an aqueous slurry containing (i) a platinum group metal-carrying zirconia, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide and calcining the resultant coating carrier, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and palladium, and (d) combination of rhodium, platinum and palladium and is deposited in a proportion in the range of 0. 5 to 30~ by weight on said æirconia powder.
A catalyst for purifying exhaust gas, consisting essentially of a honeycomb carrier of monolithic structure and a coating layer applied on said honeycomb carrier formed by a catalyst composition consisting of a first refractory inorganic oxide, free of noble metal or rhodium deposited thereon, and at least one second inorganic oxide of the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to ~ 20 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and (b) a refractory inorganic oxide having 1 to 20% by weight of : rhodium deposited thereon, and (B) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and 1 to 20% by weight of rhodium, said second inorganic oxide being in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns and being dispersed in the said coating layer, and (C) cerium oxide, free of noble metal or rhodium deposited thereon, and provided that where a member of group (C) is selected as a second inorganic oxide, at least one group (A) member or at least one group (B) member also must be present wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
- 3 -,. . .
... .
A method for the production of a catalyst for purifying exhaust gas, which consisting essentially of coating a honeycomb carrier of monolithic structure with an aqueous slurry containing a catalyst composition and subsequently calcining the coated carrier, said catalyst composition consisting of a first refractory inorganic oxide free of noble metal or rhodium deposited thereon, and a second inorganic oxide selected from the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and (b) a refractory inorganic oxide having 1 to 20% by weight of rhodium deposited thereon and (B) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and 1 to 20% by weight of rhodium, in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
We have found, as a result of a diligent study, that directly contrary to the conventional theory that the noble metal which must be used in a very minute amount ought to be deposited in a small ratio on the refractory inorganic oxide of a large surface area so as to heighten the degree of dispersion of the noble metal to the highest possible extent, a noble metal-containing refractory inorganic oxide produced by depositing the noble metal in a high ratio on a small amount of refractory inorganic oxide gives ris~ to a catalyst of surprisingly high durability when the aforementioned noble metal-containing refractory inorganic oxide is adjusted in the form of cohesive particles of a relatively large average particle diameter in the range of 0.5 to 20 microns and dispersed in a catalyst coating layer. The present invention has been made as the result.
- 3a -~ :
;EXPLANATION OF THE PREFERRED EMBODIMENTS
: The catalyst composition of the present invention - comprises (A) (a) a refractory inorganic oxide having carried therein platinum and/or (b) a refractory !
., - 3b -. . -,~ .
' ~ ' ~.: ~ , -inorganic oxide having carried thereon rhodium or (B) a refractory inorganic oxide having carried thereon platinum and rhodium and optionally incorporates therein (C) cerium oxide and/or (D) a refractory inorganic oxide S containing no deposited noble metal.
The range of the high ratio of deposition of platinum on the refractory inorganic oxide is 5 to 30%
by weight, preferably 10 to 20% by weight and 1 to 20%
by weight, preferably 1 to 10% by weight of rhodium. If 10 the ratio of deposition of platinum is less than 5% by weight or that of rhodium is less than 1% by weight, the state of dispersion approximates that in the conventional catalyst and the catalyst composition, therefore, incurs heavy degradation of catalytic lS activity. If the ratio of deposition of platinum exceeds 30% by weight or that of rhodium exceeds 20% by weight, the active sites of the noble metal which contribute effectively to the reaction are not increased but are rather decreased even at the initial stage and 20 as the result the catalyst shows poor initial activity.
j Moreover, the noble metal entails notable growth of - particle size, a phenomenon not observed where the ratio i~ of deposition falls in the range defined by the present invention. This growth of particle size results in a . 25 serious degradation of catalyst activity.
Optionally, platinum and rhodium may be (A) independently deposited on separate portions of the , refractory inorganic oxide and the noble metal-carrying refractory inorganic oxide portions consequently 30 obtained may be used either independently or as suitably combined. Otherwise, these noble metals may be (B) collectively deposited on one and the same portion of the refractory inorganic oxide. When the noble metals are collectively deposited on one and the same portion 35 of the refractory inorganic oxide, the total amount of the noble metals so deposited is desired to fall in the range of 6 to 40% by weight, preferably 11 to 30% by weight, in order for the produced catalyst to give particularly good results. The catalyst durability is improved by having platinum and rhodium deposited both in high ratios. This improvement of durability may be 5 logically explained by a supposition that the interaction between platinum and rhodium, for example, curbs the formation of irreversible rhodium oxide which is not easily reduced to an active rhodium metal. It i5 also surprising to note that no discernible inactivation 10 of the catalyst is brought about by the alloyage of platinum with rhodium so long as the ratio of deposition falls within the range specified by this invention.
The second characteristic of the present ` invention resides in the fact that the refractory 15 inorganic oxide having the noble metals deposited thereon in high ratios is dispersed in the form of particles of a relatively large particle diameter falling in the range of 0.5 to 20 microns, preferably 1 to 15 microns. By regulating the average particle 20 diameter in this range, the interaction and the reaction between the noble metals and the refractory inorgnaic oxide can be mitigated without a sacrifice of the efficiency of the reaction for purifying the exhaust gas.
Owing to the combination of the characteristics described above, the catalyst of this invention which is produced by coating a honeycomb carrier of monolithic structure with 1 to 20g, preferably 2 to 15 g, of the refractory inorganic oxide 30 having noble metals deposited thereon in high ratios and possessing an average particle diameter in the range of 0.-5 to 20 microns and 50 to 200 g, preferably 50 to 150 g, of the refractory inorganic oxide containing no noble metal, each per liter of the carrier exhibits 35 highly satisfactory durability under harsh conditions such as under a high-temperature oxidative atmosphere.
_ 5 _ .
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~ 323620 - For the platinum to be used in the present ` invention, platinic chloride, dinitro-diammine platinum, platinum-sulfite complex, platinum tetramine chloride, palladium chloride, for example, are desirable sources.
5 As rhodium sources, rhodium nitrate, rhodium chloride, .;
" rhodium sulfate, rhodium-sulfite complex, and rhodium-ammine complex are desirable.
As examples of the refractory inorganic oxide to be used in this invention, there can be cited ; 10 alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, silica-zirconia, titania-zirconia, and alumina-magnesia.
It is particularly desirable to use alumina, particularly activated alumina, among other refractory 15 inorganic oxides enumerated above. The activated ~ alumina is desired to be of a grade possessing a ;. specific surface area in the range of 5 to 200 m2/g, preferably 50 to 180m2/g. This invention does not discriminate the activated alumina on account of the ~; 20 crystalline form thereof. The activated alumina can be s used in any of all possible crystalline forms such as y, ~ , K , and n. An activated alumina which has at least one element selected from the group consisting of rare earth metals such as lanthanum, 25 cerium, and neodymium, alkaline earth elements such as calcium and barium, and metal elements such as chromium, manganese, iron, cobalt, nickel, and zirconium deposited thereon in the form of an oxide in an amount falling in the range of 0.1 to 30% by weight,preferably 0.2 to 20 %
30 by weight, is also usable.
The catalyst composition made of the , aforementioned noble metal-carrying refractory inorganic oxide may incorporate therin cerium oxide when necessary for the purpose of further enhancing the effect thereof.
As the source for the cerium oxide to be used in the present invention, any starting material can be used so long as it is capable of existing as cerium .
~, , .
~ 323620 dioxide (CeO2) in the finished catalyst. For example, commercially available CeO2, cerium carbonate, and cerium hydroxide are available as cerium oxide sources.
Alternatively, the incorporation of cerium oxide may be 5 attained by impregnating the refractory inorganic oxide with a cerium salt solution such as, for example, an aqueous cerium nitrate solution. The catalyst of this invention is enabled to manifest the properties thereof to greater advantage by using as a cerium oxide an 10 alumina-modified cerium oxide which is obtained by impregnating a water-insoluble cerium compound with at least one member selected from the group consisting of water-soluble aluminum compounds and alumina hydrates and calcining the product of impregnation.
As examples of the water-insoluble cerium compound, there can be cited cerium oxide, cerium hydroxide, and cerium carbonate. It is particularly desirable to use cerium carbonate among other cerium J, compounds cited above. This water-insoluble cerium 20 compound is used in the form of fine powder having a particle diameter in the range of 0.1 to 100 microns, preferably 0.2 to 80 microns. As examples of the water-soluble aluminum compound and/or alumina hydrate, ` there can be cited aluminum nitrate, aluminum chloride, 25 aluminum sulfate, -gypsite, bayerite, boehmite, alumina gel, and almina sol. It is especially desirable to use aluminum nitrate among other water-soluble aluminum compounds cited above.
The amounts of the water-insoluble cerium 30 compound and the water-soluble aluminum compound and/or alumina hydrate to be used are not specifically limited.
Th-e use of these compounds permits effective production ; of an alumina-modified cerium oxide. Desirably, the atomic ratio of cerium to aluminum, Ce/Al, is in the 35 range of 1 to 20, preferably 2 to 10. After the water-insoluble cerium compound is impregnated with the water-soluble aluminum compound and/or the alumina : 1 323620 .
hydrate, the product of this impregnation is generally dried at a temperature in the range of 100 to 300C and -~ then calcined in the air at a temperature in the range of 300 to 700C to give rise to an alumina-modified 5 cerium oxide.
The refractory inorganic oxide having noble ; metals deposited thereon at high ratios as specified by the present inveniton is adjusted to an average particle ^ diameter in the range of 0.5 to 20 microns. This 10 adjustment of the average particle diameter is attained, for example, by impregnating the aforementioned ;~ refractory inorganic oxide in the form of powder or pellets with noble metal compounds and then pulverizing the product of impregnation as with a mill to a desired 15 particle diameter.
This treatment gives rise to a slurry ' containing a powder of adjusted particle diameter. By wash coating a honeycomb of monolithic structure with this slurry and then calcining the coated carrier, s 20 there is obtained a finished catalyst. The calcination is performed at a temperature falling generally in the range of 100 to 600C, preferably 130 to 300C for a period in the range of 1 to 10 hours, preferably 1 to 3 hours.
~;~ 25 The honeycomb carrier of monolithic structure to be used in the first and second aspects of the present invention can be any of honeycomb carriers s referred to by the generic term "ceramic honeycomb carrier." The honeycomb carriers formed with such 30 materials as cordierite, mullite, ~ -alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, alumino silicate, and magnesium silicate prove to be particularly desirable. Those made of cordieritic substance are used particularly 35 advantageously in the catalyst for use in the internal combustion engine among other materials enumerated above. Honeycomb carriers formed in monolithic 5~ , .
:`
., , ` I 323620 structure with a metal such as stainless steel or Fe-Cr-Al alloy which is resistant to oxidation and to heat can be used too. The monolithic carrier of the preceding description can be produced, for example, by 5 the extrusion molding method or the method of tightly ^ rolling a sheetlike element. The openings (cells) formed in the monolithic honeycomb carrier for passage of the gas under treatment may be in a hexagonal, - tetragonal, trigonal, or corrugated shape. The 10 honeycomb carrier functions very satisfactorily when the cell density (number of cells per unit cross sectional area) is in the range of 150 to 600 cells/square inch.
Now, the present invention will be described more specifically with reference to working examples.
~`,A, 15 Needless to mention, this invention is not limited only to these wor~ing examples.
~? Example 1 A catalyst was prepared by using commercially available monolithic carrier pieces of cordierite 20 (produced by NGK Insulators Ltd.). The monolithic carrier pieces were cylinders measuring 33 mm in outside diameer and 76 mm in length, containing about 400 gas flow cells per square inch of cross-sectional area, and `.$ possessing a volume of about 65 ml.
An alumina powder containing 16.7% by weight of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing l.Sg of platinum with 7.5g of an activated alumina ~i possessing a specific surface area of 100 m2/g, ; 30 throroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hours.
An alumina powder containing 9% by weight of rhodium was prepared by mixing an aqueous rhodium 35 nitrate solution containing 0.3 g of rhodium with 3 g of ., .
_ g _ -: .
,', ' ' ' ~
,: .
,. .
.
., ~- - 1 323620 the same activated alumina as described above, - thoroughly drying the resultant mixture, and calcining the dried mixture in the air at 400C for 2 hours.
; An aqueous slurry for coating was prepared by 5 wet pulverizing 139g of the same activated alumina as described above, the aforementioned platinum-containing alumina powder, and the rhodium-containing alumina powder, in a ball mill for 20 hours. The aforementioned ` monolithic carrier pieces were immexsed in the aqueous ~ 10 slurry for coating, removed from the slurry, and blown " with compressed air to remove residual slurry from within the cells and relieve all the cells of clogging slurry. The wet carrier pieces were dried at 130C for 3 hours to obtain a finished catalyst.
2 15 The coating layer of this catalyst was photographed at 30 randomly selected spots through an electron prove microanalyzer (EPMA) at 3,000 magnifications to determined the conditions of platinum and rhodium distribution in the layer. It was 20 consequently confirmed that platinum-containing alumina particles and rhodium-containing alumina particles both - of an average particle diameter of S microns were dispersed in the layer. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g 25 of rhodium per liter of the catalyst.
Example 2 - A low ratio deposition alumina powder containing G.2% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 30 0.3 g of rhodium with 142 g of an activated alumina - possessing a specific surface area of 120 m2/g, drying the resultant mixture, and calcining the dried mixture in the air at 400C fox 2 hours.
;
1 32362~
A finished catalyst was obtained by following the procedure of Example 1, excepting the aforementioned rhodium-containing alumina powder was used in the place of the alumina powder containing 9~ by weight of rhodium 5 and the activated alumina used in Example 1.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was found to be dispersed in the form of particles of an average particle diameter of 6 microns and no rhodium 10 was detected as dispersed in the form of particles exceeding 0.5 microns in diameter.
This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
- 15 Example 3 A low ratio deposition alumina powder containing 1~ by weight of platinum was prepared by ~,- mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum 20 with 147 g of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, ;~ and then calcining the dried mixture in the air at 400C
for 2 hours.
-i; A finished catalyst was obtained by following 25 the procedure of Example 1, excepting the aforementioned platinum-containing alumina powder was used in the place of the alumina powder containing 16.7% by weight of `~ platinum and the activated alumina as used in Example 8.
When the coating layer of this catalyst was 30 examined by EPMA, the rhodium-containing alumina was ~- dispersed in the form of particles possessing an average p æticle diameter of 4.5 microns and no platinum was found to be dispersed in the form of particles exceeding 0.5 microns in diameter. This catalyst was found to 35 contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 4 '' ,,. , ~
., :
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.A finished catalyst was obtained by following the procedure of Example 1, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine 5 platinum. The platinum-containing alumina used in this case had 16.8% by weight of platinum deposited thereon.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was found to be dispersed in the form of particles .
10 possessing an average particle diameter of 7 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 4 microns.
` This catalyst was found to contain 100 g of alumina, l.Og of platinum, and 0.2 g of rhodium per liter of the 15 catalyst.
` Example 5 . A finished catalyst was obtained by following the procedure of Example 1, excepting an aqueous rhodium chloride solution was used in the place of the aqueous 20 rhodium nitrate solution. The rhodium-containing alumina used in this case had 8.9% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was -25 found to be dispersed in the form of particles 'e,possessing an average particle diameter of 5 microns and ;the rhodium-containing alumina in the form of particles possessing an average particle diameter of 8 microns.
~his catalyst was found to contain 100 g of alumina, 1.0 30 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 6 Metallic monolithic carrier cylinders 33 mm in diameter and 76 mm in length were formed by alternately .35 superposing flat thin sheets of aluminum-containing ferrite stainless steel 60 microns in thickness and corrugated sh~ets produced by corrugating the same flat .
---`` 1 323620 thin sheets to impart therein waves of a pitch of 2.5 mm. This carrier contained in the cross section thereof about 475 gas flow cells per square inch of cross-sectional area.
A finished catalyst was obtained by following ~! the procedure of Example 1, excepting the aforementioned metallic monolithic carrier was used in the place of the ` monolithic carrier of cordierite.
When the coating layer of this catalyst was 10 examined by EPM~, the platinum-containing alumina was ~ found to be dispersed in the form of particles ;f possessing an average particle diameter of 4 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 3.5 microns.
15 This catalyst was found to contain 100 g of alumina, l.Og of platinum, and 0.2 g of rhodium per liter of the catalyst.
~ Example 7 r'~ An aqueous slurry was obtained by wet ; 20 pulverizing 139 g of the same activated alumina as used - in Example 1 in a ball mill for 13 hours. Further an aqueous slurry for coating was obtained by wet pulverizing the a~ueous slurry and the alumina powder containing 16.7% by weight of platinum and the alumina 25 powder containing 9~ by weight of rhodium prepared in . A
Example 1 in a ball mill for 7 hours.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was ~; found to be dispersed in the form of particles 30 possessing an average particle diameter of 15 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 10 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per 35 liter of the catalyst.
- Control 1 ., ~ - 13 -" ; , . ..
' ' .
An aqueous slurry was prepared by wet pulveri~ing 150 g of an activated alumina possessing a specific surface area of 100 m2/g in a ball mill. The ~- same monolithic carrier of cordierite as used in Example - 5 1 was coated with the aqueous slurry.
In a mixed solution obtained by thoroughly - stirring an aqueous solution of the nitrate of dinitro-diammine platinum containing 0.065 g of platinum ' and an aqueous rhodium nitrate solution contaiing 0.013 10 g of rhodium, the alumina-coated carrier was immersed and allowed to adsorb thereon all the platinum and rhodium present in the solution. The carrier was removed from the soltuion, treated for removal of the residual solution from within the cells by drainage, 15 dried at 130C for 3 hours, and then calcined in the air at 400C for 2 hours, to obtain a finished catalyst.
;~ When the coating layer of this catalyst was examined by EPMA,~ neigher platinum nor rhodium were !i found to be dispersed in the form of particles exceeding ~, 20 0.5 micron in diameter. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
, Control 2 -~ An alumina powder containing 35.7% by weight 25 of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum with 2.7 g of the same activated alumina as used in Control 1, thoroughly drying the ,; resultant mixture, and then calcining the dried mixture 30 in the air at 400C for 2 hours.
An alumina powder containing 21.4% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 1.1 g of the same activated alumina as described above, 35 thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hoUrs .
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~ - 14 -, .
.
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~ - ` 1 323620 ,..
A finished catalyst was obtained by following the procedure of Example 1, using the platinum-containing alumina powder and the -: , rhodium-containing alumina powder mentioned above and 5 146 g of the same activated alumina as used above ~ instead.
; When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina and the rhodium-containing alumina were found to be 10 dispersed in the form of particles possessing an average ^ particle diameter of 6.5 microns. This catalyst was found to contain lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 3 lS An aqueous slurry was prepared by wet ` pulverizing 139 g of activated alumina pellets s possessing a specific surface area of 120 m2/g in a ball mill for l9 hours. An aqueous slurry for coating was obtained by wet pulverizing this aqueous slurry and the 20 alumina powder containing 16.7~ by weight of platinum - and the alumina powder containing 9% by weight of rhodium both prepared as in Example l in a ball mill for l hour. A finished catalyst was obtained by following ~ the procedure of Example l, using this coating slurry.
-- 25 When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was , found to be dispersed in the form of particles ; possessing an average particle diamter of 30 microns and the rhodium-containing alumina in the form of particles ~; 30 possessing an average particle diameter of 40 microns.
This catalyst was found to containg lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 4 An alumina powder contaiing 0.2% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 150 g . . .
.
,~ ': '' . ~ . .
, , ,, ~- : ' :, l.
-" 1 323620 of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 - hours.
A finished catalyst was obtained by following the procedure of Example 1, excepting the aforementioned rhodium-containing alumina powder and 1.5 g of a commercially available platinum black possessing an average particle diameter of 1.0 micron (produced by 10 Ishifuku Kinzoku Rogyo K.K.) were used instead.
When the coating layer of this catalyst was examined by EPMA, the platinum was found to be dispersed in the form of particles possessing an average particle diameter of 1 micron. This catalyst was found to 15 contain 100 g of alumina, 1.0 g of platinum, and 0.2 g ~ of rhodium per liter of the catalyst.
;~ Example 8 The catalysts of Examples 1 through 7 and the catalysts of Controls 1 through 4 were tested for ` 20 catalytic property after aging in the electorc furnace.
This aging in the electric furnace was performed by exposing a given catalyst to a ~; high-temperature oxidative atmosphere involving very harsh conditions of 10 hours' heating at 900C.
The evaluation of the catalytic property was ' carried out by using a commercially available ~, electronically controlled engine ~4 cylinders 1,800 cc), with a multi-converter packed with the catalyst under ~ treatment and connected to the exhaust system of the ; 30 engine. The engine was operated, with the air - combustion ratio, A/F, fixed at 14.6. By means of a ^ heat-exchanger which was inserted in front of the catalyst converter in the exhaust system of the engine, i the inlet gas temperature was continuously varied from 35 300C to 500C. The gas was sampled at the inlet and the outlet of the catalyst converter and analyzed to -- ; - ' .
, ~ 1 3~3620 ,.~
determine the purifying ratios of CO, HC, and NO and ; evaluate the purifying ability of the catalyst at low . temperatures.
The purifying ratios of CO, HC, and NO
. S obtained as described above as the functions of the . inlet gas temperature were plotted on a graph to find the inlet gas temperatures (T50) showing a fixed . purifying ratio of 50~. The inlet gas temperatures .. ~T50) thus determined were used as the standard for . 10 evaluation of the purifying property of catalyst at low temperatures.
~' The results obtained by the method of . evaluation of catalytic property described above are shown in Table 1.
; ~
':
- ~
.. . . . .
- ., Table 1 Evaluation of catalytic property after aging in electric furnace Purifying prc ~erty at low t ,mperatures , CO purifying HC purifying NO purifying 5 temperature, temperatue, temperature, Catalyst 50 ( ) T50 t C) T50 ( C) , Example 1 395 399 393 ,, 3 402 408 400 ~; 104 400 404 397 ~` 5 398 404 396 Control 1 465 468 465 152 450 455 ' 449
... .
A method for the production of a catalyst for purifying exhaust gas, which consisting essentially of coating a honeycomb carrier of monolithic structure with an aqueous slurry containing a catalyst composition and subsequently calcining the coated carrier, said catalyst composition consisting of a first refractory inorganic oxide free of noble metal or rhodium deposited thereon, and a second inorganic oxide selected from the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and (b) a refractory inorganic oxide having 1 to 20% by weight of rhodium deposited thereon and (B) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and 1 to 20% by weight of rhodium, in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
We have found, as a result of a diligent study, that directly contrary to the conventional theory that the noble metal which must be used in a very minute amount ought to be deposited in a small ratio on the refractory inorganic oxide of a large surface area so as to heighten the degree of dispersion of the noble metal to the highest possible extent, a noble metal-containing refractory inorganic oxide produced by depositing the noble metal in a high ratio on a small amount of refractory inorganic oxide gives ris~ to a catalyst of surprisingly high durability when the aforementioned noble metal-containing refractory inorganic oxide is adjusted in the form of cohesive particles of a relatively large average particle diameter in the range of 0.5 to 20 microns and dispersed in a catalyst coating layer. The present invention has been made as the result.
- 3a -~ :
;EXPLANATION OF THE PREFERRED EMBODIMENTS
: The catalyst composition of the present invention - comprises (A) (a) a refractory inorganic oxide having carried therein platinum and/or (b) a refractory !
., - 3b -. . -,~ .
' ~ ' ~.: ~ , -inorganic oxide having carried thereon rhodium or (B) a refractory inorganic oxide having carried thereon platinum and rhodium and optionally incorporates therein (C) cerium oxide and/or (D) a refractory inorganic oxide S containing no deposited noble metal.
The range of the high ratio of deposition of platinum on the refractory inorganic oxide is 5 to 30%
by weight, preferably 10 to 20% by weight and 1 to 20%
by weight, preferably 1 to 10% by weight of rhodium. If 10 the ratio of deposition of platinum is less than 5% by weight or that of rhodium is less than 1% by weight, the state of dispersion approximates that in the conventional catalyst and the catalyst composition, therefore, incurs heavy degradation of catalytic lS activity. If the ratio of deposition of platinum exceeds 30% by weight or that of rhodium exceeds 20% by weight, the active sites of the noble metal which contribute effectively to the reaction are not increased but are rather decreased even at the initial stage and 20 as the result the catalyst shows poor initial activity.
j Moreover, the noble metal entails notable growth of - particle size, a phenomenon not observed where the ratio i~ of deposition falls in the range defined by the present invention. This growth of particle size results in a . 25 serious degradation of catalyst activity.
Optionally, platinum and rhodium may be (A) independently deposited on separate portions of the , refractory inorganic oxide and the noble metal-carrying refractory inorganic oxide portions consequently 30 obtained may be used either independently or as suitably combined. Otherwise, these noble metals may be (B) collectively deposited on one and the same portion of the refractory inorganic oxide. When the noble metals are collectively deposited on one and the same portion 35 of the refractory inorganic oxide, the total amount of the noble metals so deposited is desired to fall in the range of 6 to 40% by weight, preferably 11 to 30% by weight, in order for the produced catalyst to give particularly good results. The catalyst durability is improved by having platinum and rhodium deposited both in high ratios. This improvement of durability may be 5 logically explained by a supposition that the interaction between platinum and rhodium, for example, curbs the formation of irreversible rhodium oxide which is not easily reduced to an active rhodium metal. It i5 also surprising to note that no discernible inactivation 10 of the catalyst is brought about by the alloyage of platinum with rhodium so long as the ratio of deposition falls within the range specified by this invention.
The second characteristic of the present ` invention resides in the fact that the refractory 15 inorganic oxide having the noble metals deposited thereon in high ratios is dispersed in the form of particles of a relatively large particle diameter falling in the range of 0.5 to 20 microns, preferably 1 to 15 microns. By regulating the average particle 20 diameter in this range, the interaction and the reaction between the noble metals and the refractory inorgnaic oxide can be mitigated without a sacrifice of the efficiency of the reaction for purifying the exhaust gas.
Owing to the combination of the characteristics described above, the catalyst of this invention which is produced by coating a honeycomb carrier of monolithic structure with 1 to 20g, preferably 2 to 15 g, of the refractory inorganic oxide 30 having noble metals deposited thereon in high ratios and possessing an average particle diameter in the range of 0.-5 to 20 microns and 50 to 200 g, preferably 50 to 150 g, of the refractory inorganic oxide containing no noble metal, each per liter of the carrier exhibits 35 highly satisfactory durability under harsh conditions such as under a high-temperature oxidative atmosphere.
_ 5 _ .
-, :
, " .
, . .
~ 323620 - For the platinum to be used in the present ` invention, platinic chloride, dinitro-diammine platinum, platinum-sulfite complex, platinum tetramine chloride, palladium chloride, for example, are desirable sources.
5 As rhodium sources, rhodium nitrate, rhodium chloride, .;
" rhodium sulfate, rhodium-sulfite complex, and rhodium-ammine complex are desirable.
As examples of the refractory inorganic oxide to be used in this invention, there can be cited ; 10 alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, silica-zirconia, titania-zirconia, and alumina-magnesia.
It is particularly desirable to use alumina, particularly activated alumina, among other refractory 15 inorganic oxides enumerated above. The activated ~ alumina is desired to be of a grade possessing a ;. specific surface area in the range of 5 to 200 m2/g, preferably 50 to 180m2/g. This invention does not discriminate the activated alumina on account of the ~; 20 crystalline form thereof. The activated alumina can be s used in any of all possible crystalline forms such as y, ~ , K , and n. An activated alumina which has at least one element selected from the group consisting of rare earth metals such as lanthanum, 25 cerium, and neodymium, alkaline earth elements such as calcium and barium, and metal elements such as chromium, manganese, iron, cobalt, nickel, and zirconium deposited thereon in the form of an oxide in an amount falling in the range of 0.1 to 30% by weight,preferably 0.2 to 20 %
30 by weight, is also usable.
The catalyst composition made of the , aforementioned noble metal-carrying refractory inorganic oxide may incorporate therin cerium oxide when necessary for the purpose of further enhancing the effect thereof.
As the source for the cerium oxide to be used in the present invention, any starting material can be used so long as it is capable of existing as cerium .
~, , .
~ 323620 dioxide (CeO2) in the finished catalyst. For example, commercially available CeO2, cerium carbonate, and cerium hydroxide are available as cerium oxide sources.
Alternatively, the incorporation of cerium oxide may be 5 attained by impregnating the refractory inorganic oxide with a cerium salt solution such as, for example, an aqueous cerium nitrate solution. The catalyst of this invention is enabled to manifest the properties thereof to greater advantage by using as a cerium oxide an 10 alumina-modified cerium oxide which is obtained by impregnating a water-insoluble cerium compound with at least one member selected from the group consisting of water-soluble aluminum compounds and alumina hydrates and calcining the product of impregnation.
As examples of the water-insoluble cerium compound, there can be cited cerium oxide, cerium hydroxide, and cerium carbonate. It is particularly desirable to use cerium carbonate among other cerium J, compounds cited above. This water-insoluble cerium 20 compound is used in the form of fine powder having a particle diameter in the range of 0.1 to 100 microns, preferably 0.2 to 80 microns. As examples of the water-soluble aluminum compound and/or alumina hydrate, ` there can be cited aluminum nitrate, aluminum chloride, 25 aluminum sulfate, -gypsite, bayerite, boehmite, alumina gel, and almina sol. It is especially desirable to use aluminum nitrate among other water-soluble aluminum compounds cited above.
The amounts of the water-insoluble cerium 30 compound and the water-soluble aluminum compound and/or alumina hydrate to be used are not specifically limited.
Th-e use of these compounds permits effective production ; of an alumina-modified cerium oxide. Desirably, the atomic ratio of cerium to aluminum, Ce/Al, is in the 35 range of 1 to 20, preferably 2 to 10. After the water-insoluble cerium compound is impregnated with the water-soluble aluminum compound and/or the alumina : 1 323620 .
hydrate, the product of this impregnation is generally dried at a temperature in the range of 100 to 300C and -~ then calcined in the air at a temperature in the range of 300 to 700C to give rise to an alumina-modified 5 cerium oxide.
The refractory inorganic oxide having noble ; metals deposited thereon at high ratios as specified by the present inveniton is adjusted to an average particle ^ diameter in the range of 0.5 to 20 microns. This 10 adjustment of the average particle diameter is attained, for example, by impregnating the aforementioned ;~ refractory inorganic oxide in the form of powder or pellets with noble metal compounds and then pulverizing the product of impregnation as with a mill to a desired 15 particle diameter.
This treatment gives rise to a slurry ' containing a powder of adjusted particle diameter. By wash coating a honeycomb of monolithic structure with this slurry and then calcining the coated carrier, s 20 there is obtained a finished catalyst. The calcination is performed at a temperature falling generally in the range of 100 to 600C, preferably 130 to 300C for a period in the range of 1 to 10 hours, preferably 1 to 3 hours.
~;~ 25 The honeycomb carrier of monolithic structure to be used in the first and second aspects of the present invention can be any of honeycomb carriers s referred to by the generic term "ceramic honeycomb carrier." The honeycomb carriers formed with such 30 materials as cordierite, mullite, ~ -alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, alumino silicate, and magnesium silicate prove to be particularly desirable. Those made of cordieritic substance are used particularly 35 advantageously in the catalyst for use in the internal combustion engine among other materials enumerated above. Honeycomb carriers formed in monolithic 5~ , .
:`
., , ` I 323620 structure with a metal such as stainless steel or Fe-Cr-Al alloy which is resistant to oxidation and to heat can be used too. The monolithic carrier of the preceding description can be produced, for example, by 5 the extrusion molding method or the method of tightly ^ rolling a sheetlike element. The openings (cells) formed in the monolithic honeycomb carrier for passage of the gas under treatment may be in a hexagonal, - tetragonal, trigonal, or corrugated shape. The 10 honeycomb carrier functions very satisfactorily when the cell density (number of cells per unit cross sectional area) is in the range of 150 to 600 cells/square inch.
Now, the present invention will be described more specifically with reference to working examples.
~`,A, 15 Needless to mention, this invention is not limited only to these wor~ing examples.
~? Example 1 A catalyst was prepared by using commercially available monolithic carrier pieces of cordierite 20 (produced by NGK Insulators Ltd.). The monolithic carrier pieces were cylinders measuring 33 mm in outside diameer and 76 mm in length, containing about 400 gas flow cells per square inch of cross-sectional area, and `.$ possessing a volume of about 65 ml.
An alumina powder containing 16.7% by weight of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing l.Sg of platinum with 7.5g of an activated alumina ~i possessing a specific surface area of 100 m2/g, ; 30 throroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hours.
An alumina powder containing 9% by weight of rhodium was prepared by mixing an aqueous rhodium 35 nitrate solution containing 0.3 g of rhodium with 3 g of ., .
_ g _ -: .
,', ' ' ' ~
,: .
,. .
.
., ~- - 1 323620 the same activated alumina as described above, - thoroughly drying the resultant mixture, and calcining the dried mixture in the air at 400C for 2 hours.
; An aqueous slurry for coating was prepared by 5 wet pulverizing 139g of the same activated alumina as described above, the aforementioned platinum-containing alumina powder, and the rhodium-containing alumina powder, in a ball mill for 20 hours. The aforementioned ` monolithic carrier pieces were immexsed in the aqueous ~ 10 slurry for coating, removed from the slurry, and blown " with compressed air to remove residual slurry from within the cells and relieve all the cells of clogging slurry. The wet carrier pieces were dried at 130C for 3 hours to obtain a finished catalyst.
2 15 The coating layer of this catalyst was photographed at 30 randomly selected spots through an electron prove microanalyzer (EPMA) at 3,000 magnifications to determined the conditions of platinum and rhodium distribution in the layer. It was 20 consequently confirmed that platinum-containing alumina particles and rhodium-containing alumina particles both - of an average particle diameter of S microns were dispersed in the layer. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g 25 of rhodium per liter of the catalyst.
Example 2 - A low ratio deposition alumina powder containing G.2% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 30 0.3 g of rhodium with 142 g of an activated alumina - possessing a specific surface area of 120 m2/g, drying the resultant mixture, and calcining the dried mixture in the air at 400C fox 2 hours.
;
1 32362~
A finished catalyst was obtained by following the procedure of Example 1, excepting the aforementioned rhodium-containing alumina powder was used in the place of the alumina powder containing 9~ by weight of rhodium 5 and the activated alumina used in Example 1.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was found to be dispersed in the form of particles of an average particle diameter of 6 microns and no rhodium 10 was detected as dispersed in the form of particles exceeding 0.5 microns in diameter.
This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
- 15 Example 3 A low ratio deposition alumina powder containing 1~ by weight of platinum was prepared by ~,- mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum 20 with 147 g of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, ;~ and then calcining the dried mixture in the air at 400C
for 2 hours.
-i; A finished catalyst was obtained by following 25 the procedure of Example 1, excepting the aforementioned platinum-containing alumina powder was used in the place of the alumina powder containing 16.7% by weight of `~ platinum and the activated alumina as used in Example 8.
When the coating layer of this catalyst was 30 examined by EPMA, the rhodium-containing alumina was ~- dispersed in the form of particles possessing an average p æticle diameter of 4.5 microns and no platinum was found to be dispersed in the form of particles exceeding 0.5 microns in diameter. This catalyst was found to 35 contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 4 '' ,,. , ~
., :
~'' ' ' , ' ' .
.A finished catalyst was obtained by following the procedure of Example 1, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine 5 platinum. The platinum-containing alumina used in this case had 16.8% by weight of platinum deposited thereon.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was found to be dispersed in the form of particles .
10 possessing an average particle diameter of 7 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 4 microns.
` This catalyst was found to contain 100 g of alumina, l.Og of platinum, and 0.2 g of rhodium per liter of the 15 catalyst.
` Example 5 . A finished catalyst was obtained by following the procedure of Example 1, excepting an aqueous rhodium chloride solution was used in the place of the aqueous 20 rhodium nitrate solution. The rhodium-containing alumina used in this case had 8.9% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was -25 found to be dispersed in the form of particles 'e,possessing an average particle diameter of 5 microns and ;the rhodium-containing alumina in the form of particles possessing an average particle diameter of 8 microns.
~his catalyst was found to contain 100 g of alumina, 1.0 30 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 6 Metallic monolithic carrier cylinders 33 mm in diameter and 76 mm in length were formed by alternately .35 superposing flat thin sheets of aluminum-containing ferrite stainless steel 60 microns in thickness and corrugated sh~ets produced by corrugating the same flat .
---`` 1 323620 thin sheets to impart therein waves of a pitch of 2.5 mm. This carrier contained in the cross section thereof about 475 gas flow cells per square inch of cross-sectional area.
A finished catalyst was obtained by following ~! the procedure of Example 1, excepting the aforementioned metallic monolithic carrier was used in the place of the ` monolithic carrier of cordierite.
When the coating layer of this catalyst was 10 examined by EPM~, the platinum-containing alumina was ~ found to be dispersed in the form of particles ;f possessing an average particle diameter of 4 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 3.5 microns.
15 This catalyst was found to contain 100 g of alumina, l.Og of platinum, and 0.2 g of rhodium per liter of the catalyst.
~ Example 7 r'~ An aqueous slurry was obtained by wet ; 20 pulverizing 139 g of the same activated alumina as used - in Example 1 in a ball mill for 13 hours. Further an aqueous slurry for coating was obtained by wet pulverizing the a~ueous slurry and the alumina powder containing 16.7% by weight of platinum and the alumina 25 powder containing 9~ by weight of rhodium prepared in . A
Example 1 in a ball mill for 7 hours.
When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was ~; found to be dispersed in the form of particles 30 possessing an average particle diameter of 15 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 10 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per 35 liter of the catalyst.
- Control 1 ., ~ - 13 -" ; , . ..
' ' .
An aqueous slurry was prepared by wet pulveri~ing 150 g of an activated alumina possessing a specific surface area of 100 m2/g in a ball mill. The ~- same monolithic carrier of cordierite as used in Example - 5 1 was coated with the aqueous slurry.
In a mixed solution obtained by thoroughly - stirring an aqueous solution of the nitrate of dinitro-diammine platinum containing 0.065 g of platinum ' and an aqueous rhodium nitrate solution contaiing 0.013 10 g of rhodium, the alumina-coated carrier was immersed and allowed to adsorb thereon all the platinum and rhodium present in the solution. The carrier was removed from the soltuion, treated for removal of the residual solution from within the cells by drainage, 15 dried at 130C for 3 hours, and then calcined in the air at 400C for 2 hours, to obtain a finished catalyst.
;~ When the coating layer of this catalyst was examined by EPMA,~ neigher platinum nor rhodium were !i found to be dispersed in the form of particles exceeding ~, 20 0.5 micron in diameter. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
, Control 2 -~ An alumina powder containing 35.7% by weight 25 of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum with 2.7 g of the same activated alumina as used in Control 1, thoroughly drying the ,; resultant mixture, and then calcining the dried mixture 30 in the air at 400C for 2 hours.
An alumina powder containing 21.4% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 1.1 g of the same activated alumina as described above, 35 thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hoUrs .
,~ .
~ - 14 -, .
.
;
~ - ` 1 323620 ,..
A finished catalyst was obtained by following the procedure of Example 1, using the platinum-containing alumina powder and the -: , rhodium-containing alumina powder mentioned above and 5 146 g of the same activated alumina as used above ~ instead.
; When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina and the rhodium-containing alumina were found to be 10 dispersed in the form of particles possessing an average ^ particle diameter of 6.5 microns. This catalyst was found to contain lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 3 lS An aqueous slurry was prepared by wet ` pulverizing 139 g of activated alumina pellets s possessing a specific surface area of 120 m2/g in a ball mill for l9 hours. An aqueous slurry for coating was obtained by wet pulverizing this aqueous slurry and the 20 alumina powder containing 16.7~ by weight of platinum - and the alumina powder containing 9% by weight of rhodium both prepared as in Example l in a ball mill for l hour. A finished catalyst was obtained by following ~ the procedure of Example l, using this coating slurry.
-- 25 When the coating layer of this catalyst was examined by EPMA, the platinum-containing alumina was , found to be dispersed in the form of particles ; possessing an average particle diamter of 30 microns and the rhodium-containing alumina in the form of particles ~; 30 possessing an average particle diameter of 40 microns.
This catalyst was found to containg lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 4 An alumina powder contaiing 0.2% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 150 g . . .
.
,~ ': '' . ~ . .
, , ,, ~- : ' :, l.
-" 1 323620 of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 - hours.
A finished catalyst was obtained by following the procedure of Example 1, excepting the aforementioned rhodium-containing alumina powder and 1.5 g of a commercially available platinum black possessing an average particle diameter of 1.0 micron (produced by 10 Ishifuku Kinzoku Rogyo K.K.) were used instead.
When the coating layer of this catalyst was examined by EPMA, the platinum was found to be dispersed in the form of particles possessing an average particle diameter of 1 micron. This catalyst was found to 15 contain 100 g of alumina, 1.0 g of platinum, and 0.2 g ~ of rhodium per liter of the catalyst.
;~ Example 8 The catalysts of Examples 1 through 7 and the catalysts of Controls 1 through 4 were tested for ` 20 catalytic property after aging in the electorc furnace.
This aging in the electric furnace was performed by exposing a given catalyst to a ~; high-temperature oxidative atmosphere involving very harsh conditions of 10 hours' heating at 900C.
The evaluation of the catalytic property was ' carried out by using a commercially available ~, electronically controlled engine ~4 cylinders 1,800 cc), with a multi-converter packed with the catalyst under ~ treatment and connected to the exhaust system of the ; 30 engine. The engine was operated, with the air - combustion ratio, A/F, fixed at 14.6. By means of a ^ heat-exchanger which was inserted in front of the catalyst converter in the exhaust system of the engine, i the inlet gas temperature was continuously varied from 35 300C to 500C. The gas was sampled at the inlet and the outlet of the catalyst converter and analyzed to -- ; - ' .
, ~ 1 3~3620 ,.~
determine the purifying ratios of CO, HC, and NO and ; evaluate the purifying ability of the catalyst at low . temperatures.
The purifying ratios of CO, HC, and NO
. S obtained as described above as the functions of the . inlet gas temperature were plotted on a graph to find the inlet gas temperatures (T50) showing a fixed . purifying ratio of 50~. The inlet gas temperatures .. ~T50) thus determined were used as the standard for . 10 evaluation of the purifying property of catalyst at low temperatures.
~' The results obtained by the method of . evaluation of catalytic property described above are shown in Table 1.
; ~
':
- ~
.. . . . .
- ., Table 1 Evaluation of catalytic property after aging in electric furnace Purifying prc ~erty at low t ,mperatures , CO purifying HC purifying NO purifying 5 temperature, temperatue, temperature, Catalyst 50 ( ) T50 t C) T50 ( C) , Example 1 395 399 393 ,, 3 402 408 400 ~; 104 400 404 397 ~` 5 398 404 396 Control 1 465 468 465 152 450 455 ' 449
4 1 462 _ 465 462 , Then, the catalysts of Examples 1 through 7 and the catalysts of Controls 1 through 4 were tested 20 for catalytic activity after the endurance test in an engine.
, This endurance test was performed by using a ',' commercially available electronically controlled engine (8 cylinders 4,400 cc), with a multi-converter packed 25 with a catalyst under test and connected to the exhaust system of the engine. The engine was operated in a mode of alternating 60 seconds' steady operation and 6 ' seconds' decelerated operation (during which period the ; supply of fuel was cut and the catalyst was exposed to - 30 harsh conditions of a high-temperatl~re oxidative atmosphere), with the catalyst exposed to 50 hours' , 'aging under conditions such that the inlet gas temperature would reach 800C during the steady , operation.
.
. .
J
, ~
.
~ - 1 323620 .~;
The evaluation of the catalytic property after the endurance test in the engine was carried out in ;~- entirely the same manner as in the evaluation of the catalytic property after the aging in the electoric ; 5 furnace described above. The data consequently o~tained ;~ were compared with those of the purifying property at low temperatures. The results are shown in Table 2 below.
. , .
Table 2 Evaluation of catalytic property < 10 after test run of engine ., .
:........................ , ,~
,Purifying pro ?ertY at low te mperatures CO purifying HC purifying 'NO purifying temperature, temperature, temperature, -~ Catalyst T50 (C) T50 ( C) T50 (C) 15 Example 1 375 380 369 ~' 4 379 385 370 Control 1 440 447 436 4 440 __ 446 436 :`:
... ..
- It is clearly noted from Tables 1 and 2 that the catalysts of Examples 1 through 7 in which refractory inorganic oxides having platinum and/or rhodium deposited in high ratios as contemplated by the 30 present invention were dispersed in the form of particles possesing an average particle diameter in the -, - ~
' , :. - . :
~; .
range of 0.5 to 20 microns invariably exhibited better catalytic properties than the catalysts of Control l which had noble metals dispersed in the conventional state. The catalyst of Control 2 which had platinum
, This endurance test was performed by using a ',' commercially available electronically controlled engine (8 cylinders 4,400 cc), with a multi-converter packed 25 with a catalyst under test and connected to the exhaust system of the engine. The engine was operated in a mode of alternating 60 seconds' steady operation and 6 ' seconds' decelerated operation (during which period the ; supply of fuel was cut and the catalyst was exposed to - 30 harsh conditions of a high-temperatl~re oxidative atmosphere), with the catalyst exposed to 50 hours' , 'aging under conditions such that the inlet gas temperature would reach 800C during the steady , operation.
.
. .
J
, ~
.
~ - 1 323620 .~;
The evaluation of the catalytic property after the endurance test in the engine was carried out in ;~- entirely the same manner as in the evaluation of the catalytic property after the aging in the electoric ; 5 furnace described above. The data consequently o~tained ;~ were compared with those of the purifying property at low temperatures. The results are shown in Table 2 below.
. , .
Table 2 Evaluation of catalytic property < 10 after test run of engine ., .
:........................ , ,~
,Purifying pro ?ertY at low te mperatures CO purifying HC purifying 'NO purifying temperature, temperature, temperature, -~ Catalyst T50 (C) T50 ( C) T50 (C) 15 Example 1 375 380 369 ~' 4 379 385 370 Control 1 440 447 436 4 440 __ 446 436 :`:
... ..
- It is clearly noted from Tables 1 and 2 that the catalysts of Examples 1 through 7 in which refractory inorganic oxides having platinum and/or rhodium deposited in high ratios as contemplated by the 30 present invention were dispersed in the form of particles possesing an average particle diameter in the -, - ~
' , :. - . :
~; .
range of 0.5 to 20 microns invariably exhibited better catalytic properties than the catalysts of Control l which had noble metals dispersed in the conventional state. The catalyst of Control 2 which had platinum
5 deposited in a ratio of not less than 30% by weight and rhodium in a ratio of not less than 20% by weight, the catalyst of Control 3 which had platinum and rhodium deposited in ratios falling in the range specified by the present invention and but had these noble metals lO dispersed in the form of particles exceeding 30 microns ,:~
- in diameter, and the catalyst of Control 4 which had noplatinum deposited on a refractory inorganic oxide invariably exhibited poor catalytic properties.
From the foregoing results, it is clear that 15 the catalysts having platinum and rhodium deposited and dispersed under the conditions contemplated by the ~` present invention incur only slight deterioration and exhibit highly satisfactory durability not only under the ordinary conditions of engine operation but also 20 udner harsh conditions as in a high-temperature oxidative atmosphere.
Exmaple 9 A finished catalyst was obtained by following the procedure of Example 1, excepting 75 g of a 25 commercially available cerium oxide powder (produced by Nissan Kigenso K.K.) was incorporated in addition to 139 ~ g of the activated alumina, the platinum-containing alumina powder, and the rhodium-containing alumina powder.
When the coating layer of this catalyst was examined by the same method as used in Example l, the platinum-containing alumina and the rhodium-containing alumina were found to be dispersed in the form of particles possessing an average particle diameter of 5 35 microns. This catalyst was found to contain lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
-- ` 1 323620 Example 10 An alumina powder containing 0.2% by weight rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 142 g 5 of an activated aluminum possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hours.
A finished catalyst was obtained by following 10 the procedure of Example 9, excepting the rhodium-containing alumina powder was used in the place of the alumina powder containing 9~ by weight of rhodium ~, plus the activated alumina used in Example 9.
When the coating layer of this catalyst was 15 examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 6 microns and no rhodium was found to be dispersed in the form of particles exceeding 0.5 microns 20 in diameter. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 11 An alumina powder containing 1% by weight of 25 platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 i g of platinum with 147 g of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried 30 mixture in the air at 400C for 2 hours.
A finished catalyt was obtained by following the procedure of Example 9, excepting the platinum-containing alumina powder was used in the place of the alumina powder containing 16.7% by weight of 35 platinum and the activated alumina used in Example 9.
- . ~ .
: ' ' ' ~ ,.... .
~When the coating layer of this catalyts was ;,examined by the same method as in Example 1, the rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle 5 diameter of 4.5 microns and no platinum was found to be dispersed in the form of particles exceeding 0.5 micron in diameter. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
10 Example 12 ~A finished catalyst was obtained by following ;the procedure of Example 9, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine `15 platinum. The platinum-containing alumina used in this case had 16.6% by weight of platinum deposited thereon.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in 20 the form of particles possessing an average particle diameter of 7 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of .25 platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 13 A finished catalyst was obtained by following the procedure of Example 9, excepting an aqueous rhodium 30 chloride was used in the place of the aqueous rhodium nitrate. The rhodium-containing alumina used in this case had 9.1% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 35 platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle -diameter of 5 microns and the rhodium-containing alumina , ~ ' ` ,' " ~'' ' ' ~'' .
in the form of particles possessing an average particle diameter of 8 microns. This catalyst was found to t' contain 100 g of alumina, 50 g of cerium oxide, 0.1 g of platinum, and 0.2 g of rhodium per liter of the 5 catalyst.
Example 14 An alumina-modified cerium oxide (atomic ratio of Ce/Al = 5) was prepared by thoroughly mixing 150 ml of an aqueous solution having dissolved therein 65.3 g 10 of aluminum nitrate [Al(NO3)3 9H2O] with 319 g of cerium carbonate powder (possessing a Ce content of 47%
by weight as CeO2), drying the resultant mixture at 130C for 5 hours, and then calcining the dried mixture in the air at 500C for 1 hour.
A finished catalyst was obtained by following the procedure of Example 9, excepting 75 g of the alumina-modified cerium oxide was used in the place of the commerically available cerium oxide powder.
When the coating layer of this catalyst was 20 examined by the same method as in Example 1, the platinum-containing aluminum and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of ~i 25 alumina, alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium.
Example 15 An alumina-modified cerium oxide ~atomic ratio of Ce/Al = 8) was prepared by thoroughly mixing 220 ml 30 of an aqueous solution having dissolved therein 54.4 g of aluminum nitrate [Al(NO3)3 9H2O3 with 426 g of cerium carbonate powder (possessing a Ce content of 47%
by weight as CeO2), drying the resultant mixture at 130C for 5 hours, and then calcining the dried mixture 35 in the air at 500C for 1 hour.
i 1 323620 .~
A finished catalyst was obtained by following the procedure of Example 9, excepting 75g of the alumina-modified cerium oxide was used in the place of ,~ the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the ` platinum-containing alumina and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 10 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic -~ ratio of Ce/Al = 8), 1.0 g of platinum, and 0.2g of rhodium per liter of the catalyst.
Example 16 An alumina-modified cerium oxide (atomic ratio of Ce/Al = S) was prepared by mixing 94.7 g of alumina sol (containing 10% by weight as alumina ), 340 g of cerium carbonate (possessing a Ce content of 47~ by weight as CeO2), and 100 ml of water, drying the 20 resultant mixture at 130C for 5 hours, and then calcining the dried mixture in the air at 500C for 1 hour.
A finished catalyst was obtained by following the procedure of Example 9, excepting 75 of the 25 alumina-modified cerium oxide was used in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the ~platinum-containing alumina and the rhodium-containing - 30 alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 of 35 rhodium per liter of the catalyst.
-Example 17 ~ . .
. ~
.
- ` 1 323620 A finished catalyst was obtained by following the procedure of Example 16, excepting the same metallic monolithic carrier as in Example 6 was used in the place of the monolithic carrier of cordierite.
5When the coating layer sf this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle ; diameter of 4 microns and the rhodium-containing alumina 10 in the form of particles possessing an average particle diameter of 3.5 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
15 Example 1~
An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 9 with 75 g of commercialy availalbe cerium .3 oxide in a ball mill for 13 hours. Further an aqueous ~ 20 slurry ~or coating was prepared by wet pulverizing the -~ aqueous slurry and the alumina powder containing 16.7%
by weight of platinum and the powder containing 9% by weight of rhodium prepared as in Example 9 in a ball mill for 7 hours. A finished catalyst was obtained by 25 following the procedure of Example 9, using the aqueous slurry for coating.
When the coating layer of this catalyst was examined by the same method as in Example 1, the iplatinum-containing alumina was found to be dispersed in 30 the form of particle possessing an average particle diameter of 15 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 10 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 35 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 5 -,~
"
, -~,~
.. ~, . .
j . .. - . .
` 1 323620 A catalyst was obtained by following the procedure of Example 9, excepting 75 g of a commercially available cerium oxide powder was incorporated in addition to 150 g of the same activated alumina as used 5 in Example 9.
When the coating layer of this catalyst was examined by the same method as in Example 1, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.
10 This catalyst was found to contain 100 g of alumina, 50 ` g of cerium oxide, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.
Control 6 A finished catalyst was obtained by following 15 the procedure of Control 2, excepting 75 g of cerium oxide was further incorporated during the course of mixture of the powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 20 platinum-containing alumina and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diamter of 8 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 25 0.2 g of rhodium per liter of the catalyst.
, Control 7 , A finished catalyst was obtained by following the procedure of Control 3, excepting 75 g of cerium oxide was further incorporated during the course of - 30 mixture of the powders.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle 35 diameter of 30 microns and the rhodium-containing alumina in the form of particles possessing an average particle diamter of 40 microns. This catalyst was found , ' ...................................................... .
.
y ----` 1 32362~
to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 8 A finished catalyst was obtained by following the procedure of Control 4, excepting 75 g of cerium oxide was further incorporated during the mixture of the powders.
When the coating layer of this catalyst was 10 examined by the same method as in Example 1, platinum was found to be dispersed in the form of particles possessing an average particle diameter of 1 micron and no rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter. This ~ 15 catalyst was found to contain 100 g of alumina, 50 g of ; cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Exmaple 19 The catalysts of Examples 9 through 18 and the 20 catalyts of Controls 5 through 8 were tested for ~` catalytic property at low temperature after the aging in an electric furnace and after the endurance test in an ~ engine by following the procedure of Example 8. The - three way performance of each catalyst evaluated by the -~ 25 same engine as Example 8. The evaluation conditions were as follows:
The catalyst inlet gas temperature was maintained at 450C, and the space velocity was adjusted to 90,000 hr . The air-fuel ratio was changed - 30 continuously from 15.1 to 14.1 with the perturbation condition of + 0.5 A/F 1.0 Hz by external control, and at the same time the catalyst inlet gas and the catalyst outlet gas were simultaniously analyzed. The CO, HC, i and NO purifying ratios of each catalyst were 35 caluculated from the inlet and outlet gas analysis data, and plotted against the air-fuel ratio on graphs. The crossover point was defined as the purifying ratio value . , .
., .
.. . .
., -`` 1 323620 at the crossing point between the CO purifying curve and the NO purifying curve. The crossover point and the HC
purifying ratio at the air-fuel ratio of the crossover point were used as the standard for evaluation of the 5 three way performance. The results are respectively shown in Table 3 and Table 4.
. Table 3 Evaluation of catalytic property after aging in electric furnace . Three way Purifying property at performance low temperatures Catalyst Crossover point CO purifying HC purifying NO purifying temperature temperature temperature O,NO HC
15 . urify- purify- T50 ( C) T50 ( C) T50 ( C) ratio(%) ratio(%~
Example S 88 87 386 390 385 . ~
__11 83 83 395 400 392 .
, ,_ !; 14 94 96 370 375 366 . 15 93 94 3?3 377 370 . 16 91 94 375 379 373 . ,-- , ,__ .
.; 18 86 86 390 395 388 .__, ,, , .
l Control 5 51 60 443 447 441 . , ._ .
- in diameter, and the catalyst of Control 4 which had noplatinum deposited on a refractory inorganic oxide invariably exhibited poor catalytic properties.
From the foregoing results, it is clear that 15 the catalysts having platinum and rhodium deposited and dispersed under the conditions contemplated by the ~` present invention incur only slight deterioration and exhibit highly satisfactory durability not only under the ordinary conditions of engine operation but also 20 udner harsh conditions as in a high-temperature oxidative atmosphere.
Exmaple 9 A finished catalyst was obtained by following the procedure of Example 1, excepting 75 g of a 25 commercially available cerium oxide powder (produced by Nissan Kigenso K.K.) was incorporated in addition to 139 ~ g of the activated alumina, the platinum-containing alumina powder, and the rhodium-containing alumina powder.
When the coating layer of this catalyst was examined by the same method as used in Example l, the platinum-containing alumina and the rhodium-containing alumina were found to be dispersed in the form of particles possessing an average particle diameter of 5 35 microns. This catalyst was found to contain lO0 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
-- ` 1 323620 Example 10 An alumina powder containing 0.2% by weight rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 142 g 5 of an activated aluminum possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hours.
A finished catalyst was obtained by following 10 the procedure of Example 9, excepting the rhodium-containing alumina powder was used in the place of the alumina powder containing 9~ by weight of rhodium ~, plus the activated alumina used in Example 9.
When the coating layer of this catalyst was 15 examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 6 microns and no rhodium was found to be dispersed in the form of particles exceeding 0.5 microns 20 in diameter. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 11 An alumina powder containing 1% by weight of 25 platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 i g of platinum with 147 g of an activated alumina possessing a specific surface area of 120 m2/g, drying the resultant mixture, and then calcining the dried 30 mixture in the air at 400C for 2 hours.
A finished catalyt was obtained by following the procedure of Example 9, excepting the platinum-containing alumina powder was used in the place of the alumina powder containing 16.7% by weight of 35 platinum and the activated alumina used in Example 9.
- . ~ .
: ' ' ' ~ ,.... .
~When the coating layer of this catalyts was ;,examined by the same method as in Example 1, the rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle 5 diameter of 4.5 microns and no platinum was found to be dispersed in the form of particles exceeding 0.5 micron in diameter. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
10 Example 12 ~A finished catalyst was obtained by following ;the procedure of Example 9, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine `15 platinum. The platinum-containing alumina used in this case had 16.6% by weight of platinum deposited thereon.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in 20 the form of particles possessing an average particle diameter of 7 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of .25 platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 13 A finished catalyst was obtained by following the procedure of Example 9, excepting an aqueous rhodium 30 chloride was used in the place of the aqueous rhodium nitrate. The rhodium-containing alumina used in this case had 9.1% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 35 platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle -diameter of 5 microns and the rhodium-containing alumina , ~ ' ` ,' " ~'' ' ' ~'' .
in the form of particles possessing an average particle diameter of 8 microns. This catalyst was found to t' contain 100 g of alumina, 50 g of cerium oxide, 0.1 g of platinum, and 0.2 g of rhodium per liter of the 5 catalyst.
Example 14 An alumina-modified cerium oxide (atomic ratio of Ce/Al = 5) was prepared by thoroughly mixing 150 ml of an aqueous solution having dissolved therein 65.3 g 10 of aluminum nitrate [Al(NO3)3 9H2O] with 319 g of cerium carbonate powder (possessing a Ce content of 47%
by weight as CeO2), drying the resultant mixture at 130C for 5 hours, and then calcining the dried mixture in the air at 500C for 1 hour.
A finished catalyst was obtained by following the procedure of Example 9, excepting 75 g of the alumina-modified cerium oxide was used in the place of the commerically available cerium oxide powder.
When the coating layer of this catalyst was 20 examined by the same method as in Example 1, the platinum-containing aluminum and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of ~i 25 alumina, alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium.
Example 15 An alumina-modified cerium oxide ~atomic ratio of Ce/Al = 8) was prepared by thoroughly mixing 220 ml 30 of an aqueous solution having dissolved therein 54.4 g of aluminum nitrate [Al(NO3)3 9H2O3 with 426 g of cerium carbonate powder (possessing a Ce content of 47%
by weight as CeO2), drying the resultant mixture at 130C for 5 hours, and then calcining the dried mixture 35 in the air at 500C for 1 hour.
i 1 323620 .~
A finished catalyst was obtained by following the procedure of Example 9, excepting 75g of the alumina-modified cerium oxide was used in the place of ,~ the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the ` platinum-containing alumina and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 10 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic -~ ratio of Ce/Al = 8), 1.0 g of platinum, and 0.2g of rhodium per liter of the catalyst.
Example 16 An alumina-modified cerium oxide (atomic ratio of Ce/Al = S) was prepared by mixing 94.7 g of alumina sol (containing 10% by weight as alumina ), 340 g of cerium carbonate (possessing a Ce content of 47~ by weight as CeO2), and 100 ml of water, drying the 20 resultant mixture at 130C for 5 hours, and then calcining the dried mixture in the air at 500C for 1 hour.
A finished catalyst was obtained by following the procedure of Example 9, excepting 75 of the 25 alumina-modified cerium oxide was used in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the ~platinum-containing alumina and the rhodium-containing - 30 alumina were both found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 of 35 rhodium per liter of the catalyst.
-Example 17 ~ . .
. ~
.
- ` 1 323620 A finished catalyst was obtained by following the procedure of Example 16, excepting the same metallic monolithic carrier as in Example 6 was used in the place of the monolithic carrier of cordierite.
5When the coating layer sf this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle ; diameter of 4 microns and the rhodium-containing alumina 10 in the form of particles possessing an average particle diameter of 3.5 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
15 Example 1~
An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 9 with 75 g of commercialy availalbe cerium .3 oxide in a ball mill for 13 hours. Further an aqueous ~ 20 slurry ~or coating was prepared by wet pulverizing the -~ aqueous slurry and the alumina powder containing 16.7%
by weight of platinum and the powder containing 9% by weight of rhodium prepared as in Example 9 in a ball mill for 7 hours. A finished catalyst was obtained by 25 following the procedure of Example 9, using the aqueous slurry for coating.
When the coating layer of this catalyst was examined by the same method as in Example 1, the iplatinum-containing alumina was found to be dispersed in 30 the form of particle possessing an average particle diameter of 15 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 10 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 35 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 5 -,~
"
, -~,~
.. ~, . .
j . .. - . .
` 1 323620 A catalyst was obtained by following the procedure of Example 9, excepting 75 g of a commercially available cerium oxide powder was incorporated in addition to 150 g of the same activated alumina as used 5 in Example 9.
When the coating layer of this catalyst was examined by the same method as in Example 1, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.
10 This catalyst was found to contain 100 g of alumina, 50 ` g of cerium oxide, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.
Control 6 A finished catalyst was obtained by following 15 the procedure of Control 2, excepting 75 g of cerium oxide was further incorporated during the course of mixture of the powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 20 platinum-containing alumina and the rhodium-containing alumina were both found to be dispersed in the form of particles possessing an average particle diamter of 8 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 25 0.2 g of rhodium per liter of the catalyst.
, Control 7 , A finished catalyst was obtained by following the procedure of Control 3, excepting 75 g of cerium oxide was further incorporated during the course of - 30 mixture of the powders.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle 35 diameter of 30 microns and the rhodium-containing alumina in the form of particles possessing an average particle diamter of 40 microns. This catalyst was found , ' ...................................................... .
.
y ----` 1 32362~
to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 8 A finished catalyst was obtained by following the procedure of Control 4, excepting 75 g of cerium oxide was further incorporated during the mixture of the powders.
When the coating layer of this catalyst was 10 examined by the same method as in Example 1, platinum was found to be dispersed in the form of particles possessing an average particle diameter of 1 micron and no rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter. This ~ 15 catalyst was found to contain 100 g of alumina, 50 g of ; cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Exmaple 19 The catalysts of Examples 9 through 18 and the 20 catalyts of Controls 5 through 8 were tested for ~` catalytic property at low temperature after the aging in an electric furnace and after the endurance test in an ~ engine by following the procedure of Example 8. The - three way performance of each catalyst evaluated by the -~ 25 same engine as Example 8. The evaluation conditions were as follows:
The catalyst inlet gas temperature was maintained at 450C, and the space velocity was adjusted to 90,000 hr . The air-fuel ratio was changed - 30 continuously from 15.1 to 14.1 with the perturbation condition of + 0.5 A/F 1.0 Hz by external control, and at the same time the catalyst inlet gas and the catalyst outlet gas were simultaniously analyzed. The CO, HC, i and NO purifying ratios of each catalyst were 35 caluculated from the inlet and outlet gas analysis data, and plotted against the air-fuel ratio on graphs. The crossover point was defined as the purifying ratio value . , .
., .
.. . .
., -`` 1 323620 at the crossing point between the CO purifying curve and the NO purifying curve. The crossover point and the HC
purifying ratio at the air-fuel ratio of the crossover point were used as the standard for evaluation of the 5 three way performance. The results are respectively shown in Table 3 and Table 4.
. Table 3 Evaluation of catalytic property after aging in electric furnace . Three way Purifying property at performance low temperatures Catalyst Crossover point CO purifying HC purifying NO purifying temperature temperature temperature O,NO HC
15 . urify- purify- T50 ( C) T50 ( C) T50 ( C) ratio(%) ratio(%~
Example S 88 87 386 390 385 . ~
__11 83 83 395 400 392 .
, ,_ !; 14 94 96 370 375 366 . 15 93 94 3?3 377 370 . 16 91 94 375 379 373 . ,-- , ,__ .
.; 18 86 86 390 395 388 .__, ,, , .
l Control 5 51 60 443 447 441 . , ._ .
6 63 __ 68 _ _ 427 430 426 .
. 7 65 72 420 425 418 , . ,., . . ,,_ .
~ 30 8 49 58 445 449 444 ,_ ., .
- 2a -1 32362~
,. . .
.
~` Table 4 Evaluation of catalytic property after test run of engine ~ .. ._ hree way Purifying property at ~7 erformacne low tPmperatures 5 'atalyst Crossover point CO purifying HC purifying NO purifying _ temperature temperature temperature ;. O,NO HC
~ urify- purify- T50 ( C) T50 ( C) T50 ( C) .j lng ing ratio(~) ratio(%:
Example ~ 87 93 356 360 350 :,.
`. lt 80 90 365 370 360 .
1] 83 92 361 365 355 1~ 86 93 358 363 351 1. 87 93 357 363 352 - 1~ 94 98 340 345 334 1' 92 97 342 346 335 , 1~ _93 97 344 349 339,~
. 189 94 353 358 347 ~' ' 20 . 1~ 85 91 360 364 354 ,, Control ' 73 83 393 401 390 . _ ._ : , 77 86 382 390 376 ~ 70 81 395 403 390 ,~
"
' 25 It is clearly noted from Tables 3 and 4 that the catalysts of Examples 9 through 18 in which -~ refractory inorganic oxides having platinum and/or rhodium deposited in high ratios as contemplated by the present invention were dispersed in the form of 30 particles possessing an average particle diameter in the range of 0.5 to 20 microns invariably exhibited better catalytic property than the catalyst of Control 5 having the noble metals deposited and dispersed in the conventional states. The catalyst of Control 6 which 35 had platinum deposited in a ratio of not less than 30%
by weight and rhodium in a r t~o of not less than 20% by , .
weight, the catalyst of Control 7 which had platinum and rhodium deposited at ratios both falling within the ranges contemplated by this invention but dispersed in the form of particles exceeding 30 microns in diameter, 5 and the catalyst of Control 8 which had no platinum deposited on a refractory inorganic oxide invariably exhibited poor properties.
The catalysts of Examples 14 through 16 which used alumina-modified cerium oxide as a cerium oxide 10 exhibited still better properties.
Example 20 ` An alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium was prepared by mixing 7.5 g of an activated alumina possessing a 15 specific surface area of 100 m /g with a mixture of an aqueous solution of the nitrate of dinitro-ammine platinum containing 1.5 g of platinum and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, thoroughly drying the resultant mixture, and then 20 calcining the dried mixture in the air at 400C for 2 ` hours.
. ~
An aqueous slurry for coating was prepared by wet pulverizing 139 g of the same activated alumina as described above and the platinum and rhodium-containing 25 alumina powder in a ball mill for 20 hours. The same `~ monolithic carrier as used in Example 1 was immersed in this aqueous slurry for coating, removed from the slurry, and then blown with compressed air to remove excess slurry from within the cells and relieve all the 30 cells of clogging slurry. Then, the wet carrier was calcined at 130C for 3 hours, to obtain a finished catalyst.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 35 platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average ~ -,: ` , ,, particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 9 An alumina powder containing 0.99% by weight of platinum and 0.2% by weight of rhodium was prepared by mixing 150 g of the same activated alumina as used in Example 20 with a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of ; 10 platinum and an aqueous rhodium nitrate solution, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 ^hours. A finished catalyst was obtained by following the procedure of Example 20, using the aforementioned 15 alumina powder containing platinum and rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was not found to be dispersed in the form of particles exceeding 0.5 20 micron in diamter. This catalyst was found to contain ~;100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 21 A finished catalyst was obtained by following 25 the procedure of Example 20, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine Gplatinum. The platinum- and rhodium-containing alumina had 16.4% by weight of platinum and 3.1% by weight of 30 rhodium deposited thereon.
-When the coating layer of this catalyst was-eXamined by the same method as in Example 1, the platir,um- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average 35 particle diameter of 7 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
j r Example 22 A finished catalyst was obtained by following the procedure of Example 20, excepting an aqueous rhodium chloride solution was used in the palce of the 5 aqueous rhodium nitrate solution. The platinum- and rhodium-containing alumina used in this had 16.1% by weight of platinum and 3.3% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was 10 examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. This catalyst was found ~ to contain 100 g of alumina, 1.0 g of platinum, and 0.2 -` 15 g of rhodium per liter of the catalyst.
Example 23 An alumina powder containing 11.4% by weight of platinum and 3.4% by weight of rhodium was prepared by mixing 7.5 g of an activated alumina possessing a 20 specific surface area of 120 m /g with a mixture of an aqueous solution the nitrate of dinitro-diammine platinum containing 1.0 g of platinum and an aqueous rhodium nitrate solution containing 0.3g of rhodium, thoroughly drying the resultant mixture, and then 25 calcining the dried mixture in the air at 400C for 2 hours.
A finished catalyst was obtained by following the procedure of Exmaple 20, excepting the platinum- and rhodium-containing alumina was used in the place of the 30 alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by EPMA, the platinum- and rhodium-containing ;~ alumina was found to be dispersed in the form of 35 particles possessing an average particle diameter of 5 ; ' ' ' ~ :
~ ` ` 1 323620 microns. This catalyst was found to contain 100 g of alumina, 0.67 g of platinum, and 0.2 g of rhodium per - liter of the catalyst.
Example 24 A finished catalyst was obtained by following the procedure of Example 20, excepting the same metallic ; monolithic carrier as used in Example 6 was used in the place of the monolithic carrier of cordierite. The platinum- and rhodium-containing alumina used in this 10 case contained 16.3% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 15 dispersed in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 , g of rhodium per liter of the catalyst.
~ Example 25 ; 20 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 20 in a ball mill for 13 hours. An aqueous slurry for coating was prepared by wet pulverizing the , aqueous slurry and the same alumina powder containing 25 16.1% by weight of platinum and 3.2% by weight of ~ rhodium as in Example 20 in a ball mill for 7 hours. A
''J finished catalyst was obtained by following the procedure of Example 20, using the aqueous slurry for `~ coating.
When the coating layer of the catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 15 microns. This catalyst was 35 found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.
Example 26 .
,, , - 1 323~2~
The catalysts of Examples 20 through 25 and the catalyst of Control 9 were tested for ca$alytic : property after aging in an electric furnace and for catalytic activity after endurance test in an engine in 5 the same manner as in Example 19. The results are shown respectively in Table 5 and Table 6.
,"
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, 's . ~ ' ~ ' : ' .
, , .
~ .
; Table 5 Evaluation of catalytic property after aging in electric furnace , Purifying pro~ erty at low te mperatures Co purifying HC purifying NO purifying , 5 Catalyst temperature, temperature, temperature, T50 ( C)T50 t C) T50 ( C) , ~
Example 20 385 390 382 . 21 390 394 388 .~ 22 388 392 385 . 24 386 390 382 .l 25 393 397 390 , Control 9 465 468 465 .
Table 6 Evaluation of catalytic property . .~
, 15 after test run of engine : .
., Purifying property at low t~ ~peratures .
Co purifying HC purifying NO purifying . Catalyst temperature, temperature, temperature, ':' T50 t C) T50 ( C) T50 ( C) ., , 20 Example 20 364 370 359 ., 21 369 375 364 . 22 367 374 361 Control 9 440 447 436 _ ,, .
.
.. .. . .
-, ~
, . .
. . .
-` 1 323620 It is clearly noted from Table 5 and Table 6 that the catalysts of Examples 20 through 25 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios contemplated by this invention 5 were dispersed in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns exhibited far better catalytic properties than the catalyst of Control 9 having noble metals deposited in the conventional state.
10 Example 27 A finished catalyst was obtained by following the procedure of Example 20, excepting 75 g of a commercially available cerium oxide powder (produced by Nissan Kigenso K.K.) was additionally used with 139 g of lS the activated alumina and the platinum- and ~, rhodium-containing alumina powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 20 dispersed in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the i' catalyst.
i, 25 Control 10 A finished catalyst was obtained by following - the procedure of Example 27, excepting 75 g of the same commercially available cerium oxide powder as used in ~: Example 27 was used in addition to the platinum- and30 rhodium-containing alumina powder obtained as in Control 9.
When the coating layer of this catalyst was examined by the same method as in Example 1, neither ,~ ~
platinum nor rhodium was found to be dispersed in the ~ 35 form of particles exceeding 0.5 micron in diameter.
:
:
, . .
, .
, , This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per ]iter of the catalyst.
Example 28 5A finished catalyst was obtained by following the procedure of Example 27, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine platinum. The platinum- and rhodium-containing alumina , 10 used in this case contained 16.0% by weight of platinum and 3.3% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found be 15 dispersed in the form of particles possessing an average particle diameter of 7 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the - catalyst.
20 Example 29 A finished catalyst was obtained by following the procedure of Example 27, excepting an aqueous rhodium chloride solution was used in the place of the aqueous rhodium nitrate solution. The platinum- and 25 rhodium-containing alumina used in this case contained 16.1% by weight of platinum and 3.1% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 30 platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. ThiS catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the 35 catalyst.
Example 30 , . . .
,,' ' : ' A finished catalyst was obtained by following the procedure of Example 27, excepting the same platinum- and rhodium-containing alumina as obtained in Example 23 was used in the place of the 5 rhodium-containing alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 10 dispersed in the form of particles possessing an average ~` particle aiameter of 5 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 0.67 -I g of platinum, and 0.2 g of rhodium per liter of the catalyst.
15 Example 31 A finished catalyst was obtained by following the procedure of Example 27, excepting the same metallic monolithic carrier as in Example 6 was used in the place of the monolithic carrier of cordierite.
When the coating layer of this catalyst was ; examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average : particle diameter of 4 microns. This catalyst was found 25 to contain 100 g of alumina, 50 g of cerium oxide, l.O g of platinum, and 0.2 g of rhodium per liter of the catalyst.
, Example 32 A finished catalyst was obtained by following 30 the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 14 was used in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was 35 examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average .;
:
.
~"` ' ' : ` ~ .
~' ' ,~
particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 5 catalyst.
Example 33 A finished catalyst was obtained by following the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 15 was used 10 in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 15 dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found - to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 8), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 20 catalyst.
Example 34 A finished catalyst was obtained by following the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 16 was used 25 in the place of the commercially available cerium oxide - powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 30 dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 35 catalyst.
Example 35 --" 1 323620 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 27 and 75 g of a commercially available cerium oxide in a ball mill for 13 hours. An aqueous 5 slurry for coating was prepared by wet pulverizing the aqueous slurry and the alumina powder containing 16.1%
by weight of platinum and 3.2% by weight of rhodium as prepared in Example 27 in a ball mill for 7 hours. A
finished catalyst was obtained by following the 10 procedure of Example 27, using the aforementioned aqueous slurry for coating.
;When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be `15 dispersed in the form of particles possessing an average particle diameter of 15 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
20 Example 36 The catalysts of Examples 27 through 35 and the catalyst of Control 10 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in `25 the same manner as in Example 19. The results are shown in Table 7 and Table 8.
' -,.
. ~
'~
.
-`` 1 323620 Table 7 Evaluation of catalytic property after aging in electric furnace .
__ _ _ _ _ hree way Purifying property at erformance low tempratures 5 Catalyst ~rossover point C0 purifying HC purifying N0 purifying temperature temperature temperature 0,N0 HC
: urify- purify- T50 ( C) T50 ( C) T50 ( C) ng lng .. ratio(%) ratio(%' ExamDle27 90 91 380 385 377 _ 3~ 85 86 390 396 388 3~ 91~ _ 92 379 385 376 3~ 94 96 370 375 367 .
. . . . .. __ .
. . .
.. _ . __ .
20 Controll~ 51 __ 60 443_ 447 441 .
" .
'' , ;
Table 8 Evaluation of catalytic property after test run of engine . .
Three way Purifying property at performance low tempratures : 5 Catalyst Crossover point CO purifying HC purifying ~
temperature temperature temperature CO,NO HC
purify- purify- T50 (C) T50 (C) T50 (C) ratio(%) ratio(%
Example2~ 90 95 348 353 341 , 28 87 93 354 360 348 ., ... , ................................................ , .
3C 85 90- 360 366 1 354 .
_ . .
: 32 95 97 340 345 334 - .
.
; 34 g3 9~ 342 _ 347 335 86 92 358 362 ~ 351 20 ControllC 73 83 393 ~ 390 -., , ', - --' It is clearly noted from Table 7 and Table 8 : that the catalysts of Examples 27 through 35 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios as contemplated by the present 5 invention were dispersed in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns invariably exhibited better properties than the catalyst of Control 10 having noble metals deposited in the conventional state. Particularly the 10 catalysts of Examples 29 through 34 which used alumina-modified oxides as cerium oxide exhibited notable satisfactory properties.
' ,~
. ' '' '~'' ' . , - ' .
. 7 65 72 420 425 418 , . ,., . . ,,_ .
~ 30 8 49 58 445 449 444 ,_ ., .
- 2a -1 32362~
,. . .
.
~` Table 4 Evaluation of catalytic property after test run of engine ~ .. ._ hree way Purifying property at ~7 erformacne low tPmperatures 5 'atalyst Crossover point CO purifying HC purifying NO purifying _ temperature temperature temperature ;. O,NO HC
~ urify- purify- T50 ( C) T50 ( C) T50 ( C) .j lng ing ratio(~) ratio(%:
Example ~ 87 93 356 360 350 :,.
`. lt 80 90 365 370 360 .
1] 83 92 361 365 355 1~ 86 93 358 363 351 1. 87 93 357 363 352 - 1~ 94 98 340 345 334 1' 92 97 342 346 335 , 1~ _93 97 344 349 339,~
. 189 94 353 358 347 ~' ' 20 . 1~ 85 91 360 364 354 ,, Control ' 73 83 393 401 390 . _ ._ : , 77 86 382 390 376 ~ 70 81 395 403 390 ,~
"
' 25 It is clearly noted from Tables 3 and 4 that the catalysts of Examples 9 through 18 in which -~ refractory inorganic oxides having platinum and/or rhodium deposited in high ratios as contemplated by the present invention were dispersed in the form of 30 particles possessing an average particle diameter in the range of 0.5 to 20 microns invariably exhibited better catalytic property than the catalyst of Control 5 having the noble metals deposited and dispersed in the conventional states. The catalyst of Control 6 which 35 had platinum deposited in a ratio of not less than 30%
by weight and rhodium in a r t~o of not less than 20% by , .
weight, the catalyst of Control 7 which had platinum and rhodium deposited at ratios both falling within the ranges contemplated by this invention but dispersed in the form of particles exceeding 30 microns in diameter, 5 and the catalyst of Control 8 which had no platinum deposited on a refractory inorganic oxide invariably exhibited poor properties.
The catalysts of Examples 14 through 16 which used alumina-modified cerium oxide as a cerium oxide 10 exhibited still better properties.
Example 20 ` An alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium was prepared by mixing 7.5 g of an activated alumina possessing a 15 specific surface area of 100 m /g with a mixture of an aqueous solution of the nitrate of dinitro-ammine platinum containing 1.5 g of platinum and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, thoroughly drying the resultant mixture, and then 20 calcining the dried mixture in the air at 400C for 2 ` hours.
. ~
An aqueous slurry for coating was prepared by wet pulverizing 139 g of the same activated alumina as described above and the platinum and rhodium-containing 25 alumina powder in a ball mill for 20 hours. The same `~ monolithic carrier as used in Example 1 was immersed in this aqueous slurry for coating, removed from the slurry, and then blown with compressed air to remove excess slurry from within the cells and relieve all the 30 cells of clogging slurry. Then, the wet carrier was calcined at 130C for 3 hours, to obtain a finished catalyst.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 35 platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average ~ -,: ` , ,, particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Control 9 An alumina powder containing 0.99% by weight of platinum and 0.2% by weight of rhodium was prepared by mixing 150 g of the same activated alumina as used in Example 20 with a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of ; 10 platinum and an aqueous rhodium nitrate solution, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 ^hours. A finished catalyst was obtained by following the procedure of Example 20, using the aforementioned 15 alumina powder containing platinum and rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was not found to be dispersed in the form of particles exceeding 0.5 20 micron in diamter. This catalyst was found to contain ~;100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
Example 21 A finished catalyst was obtained by following 25 the procedure of Example 20, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine Gplatinum. The platinum- and rhodium-containing alumina had 16.4% by weight of platinum and 3.1% by weight of 30 rhodium deposited thereon.
-When the coating layer of this catalyst was-eXamined by the same method as in Example 1, the platir,um- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average 35 particle diameter of 7 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
j r Example 22 A finished catalyst was obtained by following the procedure of Example 20, excepting an aqueous rhodium chloride solution was used in the palce of the 5 aqueous rhodium nitrate solution. The platinum- and rhodium-containing alumina used in this had 16.1% by weight of platinum and 3.3% by weight of rhodium deposited thereon.
When the coating layer of this catalyst was 10 examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. This catalyst was found ~ to contain 100 g of alumina, 1.0 g of platinum, and 0.2 -` 15 g of rhodium per liter of the catalyst.
Example 23 An alumina powder containing 11.4% by weight of platinum and 3.4% by weight of rhodium was prepared by mixing 7.5 g of an activated alumina possessing a 20 specific surface area of 120 m /g with a mixture of an aqueous solution the nitrate of dinitro-diammine platinum containing 1.0 g of platinum and an aqueous rhodium nitrate solution containing 0.3g of rhodium, thoroughly drying the resultant mixture, and then 25 calcining the dried mixture in the air at 400C for 2 hours.
A finished catalyst was obtained by following the procedure of Exmaple 20, excepting the platinum- and rhodium-containing alumina was used in the place of the 30 alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by EPMA, the platinum- and rhodium-containing ;~ alumina was found to be dispersed in the form of 35 particles possessing an average particle diameter of 5 ; ' ' ' ~ :
~ ` ` 1 323620 microns. This catalyst was found to contain 100 g of alumina, 0.67 g of platinum, and 0.2 g of rhodium per - liter of the catalyst.
Example 24 A finished catalyst was obtained by following the procedure of Example 20, excepting the same metallic ; monolithic carrier as used in Example 6 was used in the place of the monolithic carrier of cordierite. The platinum- and rhodium-containing alumina used in this 10 case contained 16.3% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 15 dispersed in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 , g of rhodium per liter of the catalyst.
~ Example 25 ; 20 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 20 in a ball mill for 13 hours. An aqueous slurry for coating was prepared by wet pulverizing the , aqueous slurry and the same alumina powder containing 25 16.1% by weight of platinum and 3.2% by weight of ~ rhodium as in Example 20 in a ball mill for 7 hours. A
''J finished catalyst was obtained by following the procedure of Example 20, using the aqueous slurry for `~ coating.
When the coating layer of the catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 15 microns. This catalyst was 35 found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.
Example 26 .
,, , - 1 323~2~
The catalysts of Examples 20 through 25 and the catalyst of Control 9 were tested for ca$alytic : property after aging in an electric furnace and for catalytic activity after endurance test in an engine in 5 the same manner as in Example 19. The results are shown respectively in Table 5 and Table 6.
,"
", . ::
, 's . ~ ' ~ ' : ' .
, , .
~ .
; Table 5 Evaluation of catalytic property after aging in electric furnace , Purifying pro~ erty at low te mperatures Co purifying HC purifying NO purifying , 5 Catalyst temperature, temperature, temperature, T50 ( C)T50 t C) T50 ( C) , ~
Example 20 385 390 382 . 21 390 394 388 .~ 22 388 392 385 . 24 386 390 382 .l 25 393 397 390 , Control 9 465 468 465 .
Table 6 Evaluation of catalytic property . .~
, 15 after test run of engine : .
., Purifying property at low t~ ~peratures .
Co purifying HC purifying NO purifying . Catalyst temperature, temperature, temperature, ':' T50 t C) T50 ( C) T50 ( C) ., , 20 Example 20 364 370 359 ., 21 369 375 364 . 22 367 374 361 Control 9 440 447 436 _ ,, .
.
.. .. . .
-, ~
, . .
. . .
-` 1 323620 It is clearly noted from Table 5 and Table 6 that the catalysts of Examples 20 through 25 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios contemplated by this invention 5 were dispersed in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns exhibited far better catalytic properties than the catalyst of Control 9 having noble metals deposited in the conventional state.
10 Example 27 A finished catalyst was obtained by following the procedure of Example 20, excepting 75 g of a commercially available cerium oxide powder (produced by Nissan Kigenso K.K.) was additionally used with 139 g of lS the activated alumina and the platinum- and ~, rhodium-containing alumina powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 20 dispersed in the form of particles possessing an average particle diameter of 4 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the i' catalyst.
i, 25 Control 10 A finished catalyst was obtained by following - the procedure of Example 27, excepting 75 g of the same commercially available cerium oxide powder as used in ~: Example 27 was used in addition to the platinum- and30 rhodium-containing alumina powder obtained as in Control 9.
When the coating layer of this catalyst was examined by the same method as in Example 1, neither ,~ ~
platinum nor rhodium was found to be dispersed in the ~ 35 form of particles exceeding 0.5 micron in diameter.
:
:
, . .
, .
, , This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per ]iter of the catalyst.
Example 28 5A finished catalyst was obtained by following the procedure of Example 27, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine platinum. The platinum- and rhodium-containing alumina , 10 used in this case contained 16.0% by weight of platinum and 3.3% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found be 15 dispersed in the form of particles possessing an average particle diameter of 7 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the - catalyst.
20 Example 29 A finished catalyst was obtained by following the procedure of Example 27, excepting an aqueous rhodium chloride solution was used in the place of the aqueous rhodium nitrate solution. The platinum- and 25 rhodium-containing alumina used in this case contained 16.1% by weight of platinum and 3.1% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the 30 platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. ThiS catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the 35 catalyst.
Example 30 , . . .
,,' ' : ' A finished catalyst was obtained by following the procedure of Example 27, excepting the same platinum- and rhodium-containing alumina as obtained in Example 23 was used in the place of the 5 rhodium-containing alumina powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 10 dispersed in the form of particles possessing an average ~` particle aiameter of 5 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 0.67 -I g of platinum, and 0.2 g of rhodium per liter of the catalyst.
15 Example 31 A finished catalyst was obtained by following the procedure of Example 27, excepting the same metallic monolithic carrier as in Example 6 was used in the place of the monolithic carrier of cordierite.
When the coating layer of this catalyst was ; examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average : particle diameter of 4 microns. This catalyst was found 25 to contain 100 g of alumina, 50 g of cerium oxide, l.O g of platinum, and 0.2 g of rhodium per liter of the catalyst.
, Example 32 A finished catalyst was obtained by following 30 the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 14 was used in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was 35 examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average .;
:
.
~"` ' ' : ` ~ .
~' ' ,~
particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 5 catalyst.
Example 33 A finished catalyst was obtained by following the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 15 was used 10 in the place of the commercially available cerium oxide powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 15 dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found - to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 8), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 20 catalyst.
Example 34 A finished catalyst was obtained by following the procedure of Example 27, excepting 75 g of the same alumina-modified cerium oxide as in Example 16 was used 25 in the place of the commercially available cerium oxide - powder.
When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be 30 dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al = 5), 1.0 g of platinum, and 0.2 g of rhodium per liter of the 35 catalyst.
Example 35 --" 1 323620 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 27 and 75 g of a commercially available cerium oxide in a ball mill for 13 hours. An aqueous 5 slurry for coating was prepared by wet pulverizing the aqueous slurry and the alumina powder containing 16.1%
by weight of platinum and 3.2% by weight of rhodium as prepared in Example 27 in a ball mill for 7 hours. A
finished catalyst was obtained by following the 10 procedure of Example 27, using the aforementioned aqueous slurry for coating.
;When the coating layer of this catalyst was examined by the same method as in Example 1, the platinum- and rhodium-containing alumina was found to be `15 dispersed in the form of particles possessing an average particle diameter of 15 microns. This catalyst was found to contain 100 g of alumina, 50 g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.
20 Example 36 The catalysts of Examples 27 through 35 and the catalyst of Control 10 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in `25 the same manner as in Example 19. The results are shown in Table 7 and Table 8.
' -,.
. ~
'~
.
-`` 1 323620 Table 7 Evaluation of catalytic property after aging in electric furnace .
__ _ _ _ _ hree way Purifying property at erformance low tempratures 5 Catalyst ~rossover point C0 purifying HC purifying N0 purifying temperature temperature temperature 0,N0 HC
: urify- purify- T50 ( C) T50 ( C) T50 ( C) ng lng .. ratio(%) ratio(%' ExamDle27 90 91 380 385 377 _ 3~ 85 86 390 396 388 3~ 91~ _ 92 379 385 376 3~ 94 96 370 375 367 .
. . . . .. __ .
. . .
.. _ . __ .
20 Controll~ 51 __ 60 443_ 447 441 .
" .
'' , ;
Table 8 Evaluation of catalytic property after test run of engine . .
Three way Purifying property at performance low tempratures : 5 Catalyst Crossover point CO purifying HC purifying ~
temperature temperature temperature CO,NO HC
purify- purify- T50 (C) T50 (C) T50 (C) ratio(%) ratio(%
Example2~ 90 95 348 353 341 , 28 87 93 354 360 348 ., ... , ................................................ , .
3C 85 90- 360 366 1 354 .
_ . .
: 32 95 97 340 345 334 - .
.
; 34 g3 9~ 342 _ 347 335 86 92 358 362 ~ 351 20 ControllC 73 83 393 ~ 390 -., , ', - --' It is clearly noted from Table 7 and Table 8 : that the catalysts of Examples 27 through 35 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios as contemplated by the present 5 invention were dispersed in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns invariably exhibited better properties than the catalyst of Control 10 having noble metals deposited in the conventional state. Particularly the 10 catalysts of Examples 29 through 34 which used alumina-modified oxides as cerium oxide exhibited notable satisfactory properties.
' ,~
. ' '' '~'' ' . , - ' .
Claims (37)
1. A catalyst for purifying exhaust gas comprising a honeycomb carrier of monolithic structure and a coating layer applied on said honeycomb carrier and formed with a catalyst composition comprising (i) a platinum group metal-supporting zirconia produced by depositing said platinum group metal on zirconia powder, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and palladium, and (d) combination of rhodium, platinum and palladium, and is deposited in proportion in the range of 0.5 to 30% by weight on said zirconia powder.
2. A catalyst according to claim 1, wherein said zirconia powder has a specific surface area of at least 10 m2/g and an average particle diameter of not more than 2,000 A as primary particles.
3. A catalyst according to claim 1, wherein the content of said zirconia powder in said catalyst composition is in the range of 0.5 to 50% by weight.
4. A catalyst according to claim 1, wherein said refractory inorganic oxide is activated alumina.
5. A catalyst according to claim 1, wherein said refractory inorganic oxide contains at least one member selected from the group consisting of cerium, lanthanum, and neodymium in proportion in the range of 0.1 to 30% by weight to said refractory inorganic oxide.
6. A catalyst according to claim 5, wherein said refractory inorganic oxide is activated alumina.
7. A catalyst according to claim 1, wherein said rare earth metal oxide is cerium oxide.
8. A catalyst according to claim 7, wherein the content of cerium oxide in said catalyst composition is in the range of 5 to 80% by weight.
9. A method for the production of a catalyst for purifying exhaust gas, which comprises coating a honeycomb carrier of monolithic structure with an aqueous slurry containing (i) a platinum group metal-carrying zirconia, (ii) a refractory inorganic oxide and (iii) a rare earth metal oxide and calcining the resultant coating carrier, wherein said platinum group metal is at least one member selected from the group consisting of (a) rhodium, (b) combination of rhodium and platinum, (c) combination of rhodium and palladium, and (d) combination of rhodium, platinum and palladium and is deposited in a proportion in the range of 0.5 to 30% by weight on said zirconia powder.
10. A catalyst for purifying exhaust gas, consisting essentially of a honeycomb carrier of monolithic structure and a coating layer applied on said honeycomb carrier formed by a catalyst composition consisting of a first refractory inorganic oxide, free of noble metal or rhodium deposited thereon, and at least one second inorganic oxide of the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and (b) a refractory inorganic oxide having 1 to 20% by weight of rhodium deposited thereon, and (B) a refractory inorganic oxide having deposited thereon to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium, and 1 to 20% by weight of rhodium, said second inorganic oxide being in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns and being dispersed in the said coating layer, and (C) cerium oxide, free of noble metal or rhodium deposited thereon, and provided that where a member of group (C) is selected as a second inorganic oxide, at least one group (A) member or at least one group (B) member also must be present wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
11. A catalyst according to claim 10, wherein the amount of said noble metal-carrying refractory inorganic oxide is in the range of 1 to 20 g per liter of said carrier.
12. A catalyst according to claim 10, wherein at least one noble metal selected from the group consisting of platinum and palladium is deposited in an amount in the range of 10 to 20% by weight and rhodium in an amount in the range of 1 to 10% by weight, respectively based on the amount of said refractory inorganic oxide.
13. A catalyst according to claim 10, wherein said refractory inorganic oxide is at least one member selected from the group consisting of alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, silica-zirconia, titania-zirconia, and alumina-magnesia.
14. A catalyst according to claim 13, wherein said refractory inorganic oxide is alumina or zirconia.
15. A catalyst according to claim 14, wherein said alumina is activated alumina.
16. A catalyst according to claim 15, wherein said activated alumina possesses a specific surface area in the range of 5 to 200 m2/g.
17. A catalyst according to claim 14, wherein said zirconia possesses a specific surface area of at least 10 m2/g and an average particle diameter of not more than 2,000 .ANG. as primary particles.
18. A catalyst according to claim 10, wherein a refractory inorganic oxide having no noble metal deposited thereon is incorporated additionally.
19. A catalyst according to claim 18, wherein the amount of said refractory inorganic oxide containing no deposited noble metal is in the range of 50 to 200 g per liter of said carrier.
20. A catalyst according to claim 18, wherein the refractory inorganic oxide containing no deposited noble metal is at least one member selected from the group consisting of alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, silica-zirconia, titania-zirconium, and alumina-magnesia.
21. A catalyst according to claim 20, wherein said refractory inorganic oxide containing no deposited noble metal is activated alumina.
22. A catalyst according to claim 21, wherein said activated alumina possesses a specific surface area in the range of 5 to 200 m2/g.
23. A catalyst according to claim 10, wherein said catalyst composition further incorporates therein cerium oxide.
24. A catalyst according to claim 23, wherein said cerium oxide is incorporated in said catalyst composition in an amount in the range of 1 to 150 g as CeO2 per liter of said carrier.
25. A catalyst according to claim 23, wherein said cerium oxide is an alumina-modified cerium oxide obtained by impregnating a water-insoluble cerium compound with at least one member selected from the group consisting of water-soluble aluminum compounds and alumina hydrates and calcining the resultant impregnation product.
26. A catalyst according to claim 25, wherein said water-insoluble cerium compound is selected from the group consisting of cerium carbonate, cerium oxide, and cerium hydroxide and said water-soluble aluminum compound is selected from the group consisting of aluminum nitrate, aluminum chloride, and aluminum sulfate.
27. A catalyst according to claim 25, wherein said alumina-modified cerium oxide has cerium and aluminum components thereof contained therein at an atomic ratio, Ce/Al, in the range of 1 to 20.
28. A catalyst according to claim 23, wherein a refractory inorganic oxide having no noble metal deposited thereon is further incorporated.
29. A catalyst according to claim 28, wherein the amount of said refractory inorganic oxide containing no deposited noble metal is in the range of 50 to 200 g per liter of said carrier.
30. A catalyst according to claim 28, wherein said refractory inorganic oxide containing no deposited noble metal is at least one member selected from the group consisting of alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, silica-zirconia, titania-zirconia, and alumina-magnesia.
31. A catalyst according to claim 30, wherein said refractory inorganic oxide containing no deposited noble metal is activated alumina.
32. A catalyst according to claim 31, wherein said activated alumina possesses a specific surface area in the range of 5 to 200 m2/g.
33. A catalyst according to claim 10, wherein said second inorganic oxide of said catalyst composition is selected from the group consisting of (A) the combination of (a) a refractory inorganic oxide having 5 to 30% by weight of platinum deposited thereon and (b) a refractory inorganic oxide having 1 to 20% by weight of rhodium deposited thereon and (B) a refractory inorganic oxide having 5 to 30% by weight of platinum and 1 to 20% by weight of rhodium deposited thereon in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns.
34. A catalyst according to claim 33, wherein said refractory inorganic oxide is alumina.
35. A catalyst according to claim 10, wherein said catalyst composition contains either (A) at least one zirconia selected from the group consisting of (a) zirconia having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and (b) zirconia having 1 to 20% by weight of rhodium deposited thereon or (B) zirconia having deposited therein 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and 1 to 20% by weight of rhodium, in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns.
36. A method for the production of a catalyst for purifying exhaust gas, which consisting essentially of coating a honeycomb carrier of monolithic structure with an aqueous slurry containing a catalyst composition and subsequently calcining the coated carrier, said catalyst composition consisting of a first refractory inorganic oxide free of noble metal or rhodium deposited thereon, and a second inorganic oxide selected from the group consisting of (A) at least one refractory inorganic oxide selected from the group consisting of (a) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and (b) a refractory inorganic oxide having 1 to 20% by weight of rhodium deposited thereon and (B) a refractory inorganic oxide having deposited thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and 1 to 20% by weight of rhodium, in the form of particles possessing an average particle diameter in the range of 0.5 to 20 microns wherein the amount of said second inorganic oxide having deposited thereon noble metal or rhodium is less than about 28.6% by weight of total refractory oxides.
37. A method according to claim 36, wherein said calcination is carried out at a temperature in the range of 100° to 600°C.
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62010009A JPS6427643A (en) | 1986-08-29 | 1987-01-21 | Catalyst for exhaust gas purification |
| JP10.009/1987 | 1987-01-21 | ||
| JP10.010/1987 | 1987-01-21 | ||
| JP62010010A JPS63229145A (en) | 1986-09-09 | 1987-01-21 | Catalyst for purifying exhaust gas |
| JP62012288A JPS63185450A (en) | 1986-09-05 | 1987-01-23 | Catalyst for purifying exhaust gas |
| JP12.289/1987 | 1987-01-23 | ||
| JP62012289A JPS63185451A (en) | 1986-09-05 | 1987-01-23 | Catalyst for purifying exhaust gas |
| JP12.288/1987 | 1987-01-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1323620C true CA1323620C (en) | 1993-10-26 |
Family
ID=27455296
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000556595A Expired - Lifetime CA1323620C (en) | 1987-01-21 | 1988-01-15 | Catalyst for purifying exhaust gas and method for production thereof |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1323620C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114849704A (en) * | 2022-04-12 | 2022-08-05 | 浙江通源环保科技有限公司 | Preparation method of noble metal catalyst |
-
1988
- 1988-01-15 CA CA000556595A patent/CA1323620C/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114849704A (en) * | 2022-04-12 | 2022-08-05 | 浙江通源环保科技有限公司 | Preparation method of noble metal catalyst |
| CN114849704B (en) * | 2022-04-12 | 2024-05-28 | 浙江通源环保科技有限公司 | Preparation method of noble metal catalyst |
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