AU604083B2 - Catalyst for purifying exhaust gas and method for production thereof - Google Patents

Description

60''4 08 3 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OF~FICE USE Class Application Number: Lodged; Form Int. Class Complete Specif ication- Lodged, Accepted:- Published: Priority: This document contains they nrneiid mnts miade inde;r Se-ction 49 and is correct foihag.

Related Art: TO BE COMPLETED BY APPLtCANT Name of Applicant: Address of Applicant: NIPPON SHOKUBAI KAGAKU KOGYO CO., LTD.

5-1, Koraibahi, Higashi-ku, Osaka, Japan Actual Inventor: TOMOH ISA OHATA EIICHI SHIRAISHI KAZUO TrJCHITANI SHINYA KITAGUCHI Address for Service: SANDERCOCK, SM'ITH BEADLE 207 Riversdale Road, Box 410) Hawthorn, Victorils, 3122 Complete Specification for the invention entitled: CATALYST FOR PURI.FYING EXHAUST GAS AND METHOD FOR PRODUCTION THEREOF The following statement Is a full description of this invention, Including the best method of performing It known to Me;-f 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 components such as hydrocarbon carbon monoxide 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 high purifying ability to the aforementioned noxious +tr components at low temperatures.

t Description of the Prior Art: j *In the, conventional noble metal-containing I *catalyst for purifying the exhaust gas, for the purpose 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 J ,high a degree of dispersion as possible on a refractory inorganic oxide of, a large surface area such as 25 activated alumina. The'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 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 the degradation of catalytic activity is rather heavy.

-1Q L ili i In this field, zirconia is used more often than not as incorporated chiefly in a carrier substrate for the purpose of stabilizing the physical properties of tie catalyst such as specific surface area. To cite a case using zirocnia as a carrier substrate for a noble metal, Japanese Patent Publication SHO 57(1982)-29,215 and Japanese Patent Laid-Open SH057(1982)-153,737 disclose a method which comprises forming on a carrier a coating layer containing alumina and zirconia and subsequently depositing a noble metal thereon. The catalyst produced by the method of this principle, however, suffers from the degradation of catalytic activity due to the same cause as mentioned above because the greater part of the noble metal is *o 15 substantially dispersed in a high ratio in the alumina.

As carrier substances incapable of interacting noble metals, particularly rhodium, zirconia No.

4,233,189) and alpha alumina No. 4,172,047) have been known in the art. Zirconia and alpha alumina 20 generally possess small surface areais. It has been pointed out, however, that the catalysts having rhodium carried on these substances have a disadvantage that S"exhibit poor initial activity and possess no 0* satisfactorily high ability to purify the exhaust gas at low temperatures after long term using.

An object'of this invention, therefore, is to provide a novel catalyst for purifying the exhaust gas C.ot and a method for the production thereof.

S" a Another object of this invention is to provide 30 a catalyst for purifying the exhuast 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 2

A

*r tel I It Iyt Ie *Lt c II C I I (It Ar The objects of the invention described above are accomplished by a catalyst for purifying the exhaust gas, pro'duced by coating a honeycomb carrier of monolithic structure with a catalyst composition comprising a platinum group metal carrying zirconia obtained by depositing the platinum group metal on zirconia powder, a refractory inorgnic oxide, and a rare earth metal oxide.

The objects are also accomplished by a method for the production of a catalyst for purifying the exhaust gas, which method comprises preparing an aqueous slurry containing a platinum group metal-carrying zirconia, a refractory inorganic oxide, and a rare earth metal oxide, coating a honeycomb carrier of monolithic 15 structure with the aqueous slurry, and subsequentl.y calcining the' resultant coated carrier.

These objects are further accomplished by a catalyst for purifying the exhaust gas, produced by coating a honeycomb carrier of monolithic structure with 20 a catalyst composition consisting of the following noble metal -containing refractory inorganic oxides, the average particle diameter of which is adjusted in the range of 0.5 to 20 microns at least one refractory inorganic oxide selected from the group consisting of a refractory inorganic oxide having carried thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and a refractory inorganic oxide having carried thereon 1 to 20% by weight of rhodium or a refractory 30 inorganic oxide having carried thereon 5 to 30% by weight of at least a noble metal selected from the group consisting of platinum and palladium and 1 to 20% by weight of rhodium.

The objects described above are also accomplished by a method for the production of a catalyst for purifying the exhaust gas, which method

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ii -4- 4 comprises preparing a catalyst composition containing refractory inorganic oxides, the average particle diameter of which is adjusted in the range of 0.5 to 20 microns at least one refractory inorganic oxide selected from the group consisting of a refractory inorganic oxide having carried thereon 5 to 30% by weight of at least one noble metal selected from the group consisting of platinum and palladium and a refractory inorganic oxide having carried thereon 1 to 20% by weight of rhodium or a refractory inorganic oxide having carried 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 and coating a S honeycomb carrier of monolithic structure with the catalyst t composition, and subsequently calcining the coated carrier.

The conventional theory is that, the noble metal which must be used in a very minute amount ought to be deposited in a small ratio of deposition on a refractory oxide of a large surface area so that the degree of depression of the noble metal is as higih as possible. However, the applicants have found, contrary to this conventional theory, that a noble metal-containing refractory inorganic oxide produced by depositing the noble metal in a high ratio of deposition on a small amount of refractory Inorganic oxide gives rise 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 to 20 microns and dispersed in a catalyst coating layer. The present invention has been perfected as the result.

EXPLANATION OF THE PREFERRED EMBODIMENTS amspe.004/nippon 90 8 The catalyst composition in the first aspect of this invention comprises a zirconia having deposited thereon .a platinum group metal at lea5. a rhodium-containing, a refractory inorganic oxide, and a rare earth metal oxide.

The zirconia to be used in the first aspect of this invention possesses a specific surface area exceeding 10 m2/g, preferably falling in the range of to 100 m2/g. The primary particles of this zirconia possess an average particle diameter of not more than 2,000 A, preferably not more than 500 A. A commercially available zirconia may be used on condition that it satisfies these requirements. Otherwise the zirconia may be prepared, for example, by a method which 15 comprises neutralizing an aqueous solution of zirconium I t salt as with ammonia, washing the product of neutralization, drying and calcining the washed product.

The amount of the zirconia to be used 2 generally is in the range of 0.5 to 50% by weight, based :j 20 on the amount of the catalyst composition. Even when it is used in an amount falling in the range of 0.5 to by weight, the produced catalyst composition is capable Sof fully manifesting the effect contemplated by the invention. If the amount of the zirconia exceeds 50' by weight, the individual particles of zirconia gain in Sgrowth of particle diameter 'at an accelerated rate possibly to impair the catalytic activity of the composition. The platinum group metal deposited on the zirconia required to incorporate therein rhodium.

30 Further incorporation of platinum or palladium is observed to bring about an improvement further in the low-temperature activity of the catalyst after long term using" at elevated temperatures. The total amount of platinum and palladium to be incorporated in addition to rhodium desirably falls in the range of 1/5 to 5 in gravimetric ratio, based on the amount of rhodium.

Thus, the noble metal-carrying zirconia 5 contains such noble metals in a total concentration falling in the range of 0.5 to 30% by weight, preferably 1 to 20% by weight.

The platinum group metal except for rhodium is not required to be wholly deposited on the zirconia. It may be deposited on a refractory inorganic oxide such as alumina or on a rare earth metal oxide. The deposition of the noble metal on the zirconia may be effected uy any of the conventional methods and need not be carried out by any specific method. Rhodium chloride, rhodium nitrate, and rhodium sulfate can be used as rhodium sources and platinic chloride, dinitrodiammine platinum, palladium chloride, and palladium nitrate as platinum or paladium sources, all in the form of an aqueous solution 15 or an alcoholic solution. Where two or more platinum lt> group metals are to be deposited on the zirconia, this t deposition may be effected by impregnating the metals either separately or collectively in the solution.

Then, by drying and calcining the impregnated zirconia, the noble metals are deposited fast on the zirconia.

As examples of the refractory inorganic oxide to be used effectively in the first aspect of the t t present invention, there may be cited alumina, silica, titania, magnesia, and zirconia. It is desirable to use alumina, particularly activated alumina among other refractory inorganic oxides cited above. This alumina may be used in any of possible crystalline forms such as t y, a a and r Though the refractory inorganic oxide may be directly incorporated in the 1 30 unmodified form in the catalyst composition, it is blcd to- oe-tribute to further enhance the catalyst composition's purifying ability by incorporating therein rare 'earth metals and such base metal elements as chromium, manganese, iron, cobalt, nickel, and zirconium in the form of oxides in a total amount falling in the -6 i i i aila~ -7range of 0.1 to 30% by weight, preferably 2 to 20% by weight, based on the amount of the refractory inorganic oxide such as, for example, alumina.

As examples of the rare earth metal oxide, there can be cited the oxides of cerium, lanthanum, and neodymium. It is particularly desirable to use cerium oxide among other rare earth metal oxides enumerated above.

The rare earth metal oxide can be deposited on the refractory inorganic oxide such as alumina as mentioned above in an amount falling in the range of 0.1 to 30% by weight, preferably 2 to 20% by weight. Otherwise, it can be t'tt incorporated directly in the catalyst composition in the form of oxide, carbonate or hydroxide, which may be converted into a corresponding oxide by calcining or through actual use. In the latter case of incorporation, the oxide can be incorporated in the catalyst composition in an amount falling t in the range of 5 to 80% by weight, preferably 10 to 50% by weight.

In the first aspect of the present invention, if the 2 0 platinum group metal, particularly the platinum group metal containing rhodium, is stably deposited on the zirconia in the form of microfine particles possessing a very large surface S, area, the possible adverse effects arising from the interaction between the carrier substance, the rare earth metal oxide, and the base metal oxide is curbed and the catalyst composition is able to incorporate therein the rare earth metal oxide and the base metal oxide in larger amounts than heretofore permitted and, as tl\e result, the catalyst composition is allowed to possess notably improved durability and purifying ability, The zirconia having deposited therein the platinum group metal, particularly the platinum group metal containing rhodium, the rare earth group oxide, and the refractory inorganic oxide which have been amspe.004/nippon 90 8 i~ 416 tilt tII 4t 4 4 44 4 *4 *I 4 4444C 4 4 41 4*E obtained as described above are ground and stirred as in a ball mill to produce an aqueous slurry. A finished catalyst is then produced by coating a honeycomb carrier of monolithic structure with the aqueous slurry, and optionally calcining the dried carrier. This calcining is performed at a temperature in the range of 100* to 600 0 C, preferably 1300 to 300 0 C for a period in the range of 1 to 10 hours, preferably 1 to 3 hours.

The catalyst composition in the second aspect of the present invention comprises a refractory inorganic oxide having carried therein platinum and/or palladium and/or a refractory inorganic oxide having carried thereon rhodium or a refractory inorganic oxide having carried thereon platinum and/or palladium and rhodium and optionally incorporates therein (C) cerium oxide and/or a refractory inorganic oxide containing no deposited noble metal.

The range of the high ratio of deposition of the noble metal on the refractory inorganic oxide is to 30% by weight, preferably 10 to 20% by weight, in the case of platinum and/or palladium and 1 to 20% by weight, preferably 1 to 10% by weight, in the case of rhodium. If the ratio of deposition of platinum and/or palladium is less than 5% by weight or that of rhodium 25 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 activity. If the ratio of deposition of platinum and/or palladium exceeds 30% by weight or that of rhodium exceeds 20% by weight, the active sites of the noble metal Which contribute effecti.vely to the reaction are not increased but are rather decreased even at the initial stage and as the result the caalyst shows poor initial activity.

Moreover, the noble metal entails notable growth of particle size, a phenomenon not observed where the ratio 8 CUi~i; i of deposition falls in the range defined by the present invention. This growth of particle size results in a serious degradation of catalyst activity.

Optionally, platinum and/or palladium and rhodium may be independently deposited on separate portions of the refractory inorganic oxide and the noble metal-carryin- refractory inorganic oxide portions consequently obtained may be used either independently or as suitably combined. Otherwise, these noble metals may be 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 of the refractory inorganic oxide, the total amount of the noble metals so deposited is desired 15 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 satisfactory results. The catalyst durability is improved by having platinum and/or palladium and rhodium deposited both in high ratios. This improvement of durability may be 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 is also surprising to note that no discernible inactivation 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 cha,; teristic of the second aspect of the present invention resides in the fact that the refractory 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 diameter in this range, the interaction and the reaction between the noble metals and the refractory 9 1~ I -cl.

I

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 preferably 2 to 15 g, of the refractory inorganic oxide having noble metals deposited thereon in high ratios and possessing an average particle diameter in the range of to 20 microns and 50 to 200 g, preferably 50 to 150 g, of the refractbry inorganic oxide containing no noble metal, each per liter of the carrier exhibits highly satisfactory durability under harsh conditions 15 such as under a high-temperature oxidative atmosphere.

For the platinum and palladium to be used in the second aspect, platinic chloride, dinitro-diammine platinum, platinum-sulfite complex, platinum tetramine chloride, palladium chloride, and palladium nitrate, for example, are desirable sources. 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 ised in this invention, there can be cited alumina, silica, titania, zirconia, alumina-silica, alumina-titania, alumina-zirconia, silica-titania, I silica-zirconia, titania-zirconia, and alumina-magnesia.

S It is 'particularly desirable to use alumina, particularly activated alumina, and zirconia among other refractory 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 crystalline form thereof. The activated alumina can be used in any of all possible crystalline forms such as 10 y 6 a K and n An activated alumina which has at least one element selected from the group consisting of rare earth metals such as lanthanum, 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 by weight, is also usable.

13 In the case of using a zirconia in this invention, it is desirably possesses the zirconia to be used in this invention possesses a specific surface area 2 exceeding at least..10 ,m preferably falling in the range of 60 to 100 m2/g, and an average primary particle 15 diameter not exceeding 2,000 A, preferably not exceeding S"500 A.

A commercially available zirconia may be used so long as it possesses the physical properties specified above. The zirconia of the foregoing description may be prepared, for example, by neutralizing an aqueous solution of zirconia salt as with ammonia and washing with water, drying, and calcining the product of the neutralization. A zirconia which is stabilized with not more than 10% by weight, preferably not more than 8 by weight, of yttrium or an alkaline earth metal such as calcium 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.

r As the source for the cerium oxide to be used in the second aspect of the present invention, any starting material can be used so long as it is capable of existing as cerium dioxide (CeO 2 in the finished catalyst. For example, commercially available Ce2', cerium carbonate, and cerium hydroxide are available as cerium oxide sources. Alternatively, the incorporation 11 ol of cerium oxide may be attained by impregnating the refractory inorganic oxide with a cerium salt solution such 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 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 1 15 desirable to use cerium carbonate among other cerium compounds cited above. This water-insoluble cerium 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, aluminum sulfate, gypsite, bayerite, boehmite, alumina gel, and almina sol. It is especially desirable to use aluminum nitrate among other water-solubl um compounds cited above.

The amounts of the water-insoluble ~um compound and the water-soluble aluminum compound and/or alumina hydrate to be used are not specifically limitLed.

The 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 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 tha alumina hydrate, the pwoduct of this impregnation is generally dried at a temperature in the range of 100* to 300sO and 12 W* ~i then calcined in the air at a temperature in the range of 300 to 700°C to give rise to an alumina-modified cerium oxi'de.

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 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' particle diameter.

This treatment gives rise to a slurry L 15 containing a powder of adjusted particle diameter. By wash coating a honeycomb of monolithic structure with I this slurry and then calcining the coated carrier, there is obtained a finished catalyst. The calcination is performed at a temperature falling generally in the range of 100 to 600°C, preferably 130 to 300°C for a period in the range of 1 to 10 hours, preferably 1 to 3 hours.

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 referred to by the generic term "ceramic honeycomb materials as cordierite, mullite, a -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 advantageously in the catalyst for use in the internal combustion engine among other materials enumerated above. Honeycomb carriers formed in monolithic structure with a metal .vh as stainless steel or Fe-Cr-Al alloy which is resistant to oxifation and to 13 heat can be used tr. The monolithic carrier of the preceding description can be produced, for example, by the ext-'~qion 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 :reatment may be in a hexagonal, tetragonal, trigonal, or corrugated shape. The 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.

Needless to mention, this invention is not limited only to these working example.

15 Example 1 f A 10.0-g portion of zirconia possessing a 2 specific surface area of 70 m /g and an average particle 1 diameter of 200 A (produced by Daiichi Kigenso kagaku was impregnated with an aqueous rhodium chloride solution containing 0.3 g of rhodium and the impregnatec.

zirconia was dried at 120 0 C for 12 hours. Then, the dried zirconia was calcined in the air at 500 0 C for 1 S* hour, to produce zirconia powder containing 2.9% by wt ,weight of rhodium. Then, 150 g of activated alumina possessing a specific surface area of 150 m2/g was impregnated with an aqueous platinic chloride solution containing 1.5 g of platinum. The impregnated activated Salumina was dried at 150°C for 12 hours and then calcined in the air at 500°C for 1 hour, to afford a platinum-containing alumina powder. In a ball mill, the two powders obtained as described above and 75 g of commercially available cerium oxide powder were wet pulverized for 20 hours, to prepare an aqueous slurry.

Monolithic carrier pieces of cordierite 33 mm in outside diameter and 76 mm in length containing about 400 gas flow cells per square inch of crois-sectional area were immersed in the aforementioned slurry, removed from the 14

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r slurry, then blown with compressed air to remove excess slurry from inside the cells, and dried at 140°C for 3 hours, to produce a catalyst A. This catalyst A, on analysis by the fluorescent X-ray, was found to contain 0.056 g of platinum and 0.011 g of rhodium per catalyst piece.

Example A zirconia powder containing 1.8% by weight of rhodium and 8.9% by weight of platinum was prepred by impregnating 15.0 g of the same zirconia powder as used in Example 1 in a mixture of an aqueous rhodium chloride solution containing 0.3 g of rhodium with an aqueous platinic chloride solution containing 1.5 g of plainum, drying the product of impregnation at 120°C for 12 *15 hours, and then calcining the dried powder in the air at l 500'"C for 1 hour. In a ball mill, the zirconia powder S and 145 g of the same activated alumina as used in Example 1 and 75 g of cerium oxide were wet pulverized for 20 hours, to produce an aqueous slurry. A catalyst B was obtained by following the procedure of Example 1 using-this aqueous slurry. The catalyst B was found to contain 0.052 g of platinum and 0.010 g of rhodium per catalyst piece.

Example 3 A catalyst C was obtained by following the procedure of Example 2, excepting a powder (iron-containing activated alumina) produced by impregnating 140 g of activated alumina with a solution of 25.3 g of ferric nitrate in 100 g of purified water and drying and calcining the product of impregnation was .used in the place of the activated alumina of Example 2.

The catalyst C was found to contain 0.054 g of platinum and 0.011 g of rhodium per catalyst piece.

Control 1 An aqueous slurry was prepared by wet pulverizing 160 g of the same activated alumina and 75 g of the same cerium oxide as used in Example 1 in a ball 15 :1 mill for 20 hours. Then, by following the procedure of Example 1, monolithic carrier pieces of cordierite were wash coated with the aqueous slurry, dried at 140 0 C for 3 hours, and then calcined in the air at 500*C for 1 hour. The monolithic carrier pieces so treated were immersed in a mixed aqueous solution of platinic chloride and rhodium chloride, dried and calcined in the air at 400 0 C for 1 hours, to produce a catalyst I. This catalyst I was found to contain 0.055 g of platinum and 0.011 g of rhodium per carrier piece.

Control 2 An aqueous slurry was prepared by wet pulverizing 120 g of the same activated alumina as used in Example 1 and 120 g of a commercially available zirconia powder in a ball mill for 20 hours. Then, by r following the procedure of Example 1, monolithic carrier pieces of cordierite were wash coated with the aqueous slurry, dried at 140°C for 3 hours, and calcined in the air at 500"C for 1 hour. The monolithic carrier pieces so treated were immersed in a mixed aqueous solution of platinic chloride and rhodium chloride, dried, and calcined in the air at 400 0 C for 1 hour, to produce as catalyst II. This catalyst II was found to contain 0.056 g of platinum and 0.011 g of rhodium per carrier piece.

Example 4 A zirconia powder containing 2.3% by weight of rhodium and 20.3% by weight of palladium was prepared by immersing 12.0 g of zirconia possessing a specific 2surface area of 90 m /g and an average particle diameter of 150 A (produced by Daiichi Kigenso Kagaku in a mixture of an aqueous rhodium nitrate solution containing 0.35g of rhodium with an aqueous palladium nitrate solution containing 3.15 g of palladium, drying the product of immersion at 120°C for 12 hours, and then calcining the dried immersion product in the air at 500*C for 1 hour.

16 ~srar--a -7 C i An alumina powder containing Ce02 and Fe 2 03 was obtained by dissolving 56.1g of cerium nitrate and 32.2 g of ferric nitrate in 200 g of purified water, mixing the resultant mixture with 200 g of an activated alumina possessing a specific surface area cf 100 m2 /g, drying the wet mixture at 120 0 C for 12 hours, and then calcining the dried mixture in the air at 700°C for 1 hour. An aqueous slurry was prepared by wet pulverizing the two powders obtained as described above in a ball mill for 20 hours. By following the procedure of Example 1, monolithic carrier pieces of cordierite were wash coated with the aqueous slurry and dried at 140°C for 3 hours, to produce a catalyst D. This catalyst D was found to contain 0.120 g of palladium and 0.013 g of 15 rhodium per carrier piece.

Example A zirconia powder containing 2.8% by weight of rhodium and 2.8% by weight of palladium was prepared by immersing 12.0 g of the same zirconia as used in Example 4 in a mixture of an aqueous rhodium nitrate solution containing 0.35 g of rhodium with an aqueous palladium nitrate solution containing 0.35 g of palladium, drying the product of imm-ne2sion at 120°C for 12 hours,, and then calcining the dried product in the air at 500°C for 1 hour.

Then, an aqueous solution of 56.1 g of cerium nitrate and 32.2 g of ferric nitrate in 200 g of purified water and an aqueous palladium nitrate solution containing 2.8 g of palladium were mixed. The resultant mixed solution was mixed with 200 g of an activated alumina possessing a specific surface area of 100 m2/g, dried at 1201C for 12 hours, and then calcined in the aix at 6000C for 1 hour. In a ball mill, the two powders obtained as described abo% were wet pulverized for 20 hours, to produce an aqueous slurry. Then, a catalyst E was obtained by following the procedure of 17 Example 1 using the aqueous slurry. This catalyst E was found to contain 0.121 g of palladium and 0.013 g of rhodium per carrier piece.

Example 6 An aqueous slurry was prepared by wet pluverizing a zirconia powder containing by weight of rhodium and 20.3% by weight of palladium prepared by following the procedure of Example 4, 150 g of an activated alumina possessing a specific surface area of 0 90 and 80 g of cerium oxide in a ball mill for hours. A catalyst F was obtained by following the procedure of Example 1 using the aqueous slurry. This S r* catalyst F was found to contain 0.115 g of palladium and 0.012 g of rhodium per catalyst piece.

o 15 Control 3 ts A solution of 56.1 g of cerium nitrate and *32.2 g of ferric nitrate in 200 g of purified water was mixed with 200 g of an activated alumina possessing a 2 specific surface area of 100 m2/g, dried at 120°C for 12 hours, and then calcined in the air at 700*C for 1 hour.

An aqueous slurry was prepared by wet pulverizing the powder obtained as described above in a ball mill for hours. Then, by following the procedure of Example 1, monolithic carrier pieces of cordierite were wash coated with the aqueous slurry, dried at 140°C for 3 hours, and calcined in the air at 500 0 C for 1 hour. A catalyst III was obtained by immersing the monolithic carrier pieces so treated in a mixed aqueous solution of palladium chloride and rhodium chloride, drying the product of immersion, and then calcining the dry product in the air at 400*C for 1 hour. This catalyst III was found to contain 0.123 g of palladium and 0.013 g of rhodium per carrier piece.

Control 4 A powder possessing a specific surface area of m /g and an average particle diameter of 5,000 A was obtained by calcining a commerically available zirconia 18 at l,000*C for 10 hours. k crtalyst IV was obtained by following the procedure of Example 4, excepting the zirconia mentioned above was instead. The catalyst IV was found to contain 0.120 g of palladium and 0.013 g of 3 rhodium per carrier piece.

Example 7 The catalysts of Examples 1 through 3 and the catalysts of Controls 1 and 2 were tested for catalytic property during initial use an," after aging in an electric furnace. The aging in the electric furnace was carried out in a high -temperature oxidative atmosphere of air involving very harsh conditions of 900 0 C and hours.

The evaluation of catalytic property was 15 performed with an electronically controlled engine (4 cylinders 1,800 cc) with the gas temperature at the inlet to a catalyst bed continuously varied from 200*C to 450*C with a heat-exchanger to determine purifying ratios of COr HC, and Nox. During this evaluation, the engine was operated as vibrated at a rate of 1 Hz, with the space velocity of gas fixed at 90,000 hr 1 an the average air comustion ratio, A/F, at 14. The inlet gas temperatures which the purifying ratios of CO, HC, and Nox reached 50% were as shown in Table 1.

The catalyst of Examples 1 through 3 and the catalysts of Controls l and 2 were also tested for A catalytic property after test run of engine. This test was carried out with an electronically controlled engine (8 cylinder 4,400 cc). With this motor operated in a mode of alternating 60 seconds' steady operation and 6 seconds' decelerated operation (during which period the fuel, supply was cut and the catalyst was exposed to a high-temperature oxidative atmosphere) to effect hours' aging of the catalyst under conditions such that the catalyst temperature would reach 850*C in the steady operation.

19 The evaluation of the catalyst property after U the test run of /engine was carried out by the same procedure as described above. The results are shown in Table 2.

Then the catalyst of Examples 4 through 6 ;tnd the catalysts of Controls 3 and 4 were tested for catalytic property during initial use and after hours' test run of engine. An electronically controlled engine (6 cylinders 2,400 cc) was used for the test run of engine mentioned above. The enduranoe test of engine was performed in a -mode of alternating 30 seconds' exposuce to an oxygen-lean atmosphere and as long cc t exposure to an oxygen-rich atmosphere, introducing secondary air thereby varying the air combustion ratio, A/F, between 14.5 and 17.5. During -the test, the '4Ig catalyst tempcrature reached the maximum of 950*C.

The evaluation of catalytic property was performed with the same engine as used for the endurance test under the conditions of A/F 14. 6 and SV approximately 140,000 hr, to determined the purifying ratios of HC, CO and NO. In the test during the initial use, the evalution was made at an inlet temperature of 500 0 C. In the test after the engine endurance test, the evalution was made at two inlet temperatures of 500*C and 700*C. The results are shown in Tables 3 and 4.

C L It is clearly noted from the results that the catalysts of Examples 1 through 3 and the catalysts of Examples 4 through 6 having noble metals deposited on zirconia of large surface area and minute particle diameter possessed highly desirable, initial properties 20 t t itt, itt, 9# I I ttt~ tIlt

I

and exhibited very high durability even after harsh endurance conditions as in a high-temperature oxidative atmosphere.

Table 1 Initial activity After agi ng in Ielectric furnace 50% conversion 50% conversion temp erature 0 C) temperature HC _NOx CO HC Nox Example 1 Catalyst A 265 268 264 391. 398 390 2 B 254 259 255 379 383 380 3 C 254 256 249 371 375 367 Control 1 7260 264 258 436 443 433 2 11 258 262 254 415 423 412 Tabl~e 2 After aging by engine conversion Purifyging ratio at ',,temperature 450 0 C CO B C. NOx CO "BC NOx Example 1 Catalyst A 359 1368 355 95 93 93 2 B 341 347 337 97 95 94 3 C 340 345 333 97 96 Control, 1 I 389 397 388 85 88 88 2 II 395 402 391 79 83 21 Table 3 e 1 4144 4 4t s 4 .4 41 *414 ttt~ 4 *44 4~ 4 Initial activity Purifying ratio at 500 0 C HC NOx Example 4 C4!talyst D 95 95 93 E 96 97 94 6 F 97 98 97 Control 3 111 96 97 94 IV 88 90 87 Table 4 After aging by engine Purifying rtio at jPurifying ratio at 5000C __J700 0 C Co HC NO CO lIC NO Exaxnp-'e 4 Catalyst D 76 85 74 88 93 87 E 82 88 78 91. 94 89 6 F s0 88 77 92 95 88 Control 3 111 62 71 59 75 82 73 4 IV 61 73 56 81 86 79 Example 8 A ca*talyst was prepared by using commercially available monolithic carrier pi~ices of cordierite (produced by NGK Insulatprs Ltd.), The monolithic carrier pieces were cylitders measuring 33 mm, in outside diaxneer 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, 22

-I-

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 of platinum with 7.5g of an activated alumina 2 possessing a specific surface area of 100 m throroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400*C for 2 hours.

An alumina powder containing 9% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 3 g of the same activated alumina as described above, K thoroughly drying the resultant mixture, and calcining the dried mixture in the air at 400*C for 2 hours.

An aqueous slurry for coating was prepared by 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 immersed in the aqueous slurry for coating, removed from the slurry, and blown with compressed air to remove residuel slurry from within the cells and relieve all the cells of clogging slurry. The wet carrier pieces were dried at 130*C for 3 hours to obtain a finished catalyst.

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 consequently confir=med that platinum-containing alumina particles and rhodiua-containing alumina particles both of an average parlicle diameter of 5 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 of rhodium per liter of the catalyst.

Example 9 23 A low ratio deposition alumina powder containing 0.2% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution containing 0.3 g of rhodium with 142 g of an activated alumina 2 possessing a specific surface area of 120 m drying the resultant mixture, and calcining the dried mixture in the air at 400 0 C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 8, excepting the aforementioned rhodium-containing alumina powder was used in the place of the alumina powder containing 9% by weight of rhodium and the activated alumina used in Example 8.

.When the coating layer of this catalyst was examined ;y EPMA, the platinum-containing alumina was found to be dispersed in the form of particles of an Saverage particle diameter of 6 microns and no rhodium Swas 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.

Example 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 with 147 g of an activated alumina possessing a specific surface area of 120 m drying the resultant mixture, and then calcining the dried mixture in the air at 400"C for 2 hours.

SI A finished catalyst was obtained by following the procedure of Example 8, 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 examined by EPMA, the rhodium-containing alumina was dispersed in the form of particles possessing an average 24 r. T When the coating layer of this catalyst was examined by EPMA, the rhodium-containing alumina was dispersed in the form of particles possessing an average particle diameter of 4.5 microns and no platinum was found to be dispersed in the form of particles exceeding 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.

)Example 11 A finished catalyst was obtained by following the procedure of Example 8, excepting an aqueous platinic chloride solution was used in the place of the aqueous solution of the nitrate of dinitro-diammine i" platinum. The platinum-containing alumina used in this 15 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 possessing an average perticle 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, of platinum, and 0.2 g of rhodium per liter of the catalyst.

2$ Example 12 A finished catalyst was obtained by following the procedure of Example 8, excepting an aqueous rhodiui chloride solution was used in the place of the aqueous rhodium nitrate solution. The rhodium-containing alumina used in this case had 8.9% by weight of rhodium Ar 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 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.

25 I II IC Example 13 Metallic monalith cQae r cylinders 33 mm in diameter and 76 mm in length wer£, formed by alternately superposing flat thin sheets? of aluminum-containing ferrite stainless steel 60 Auicsovns in thickness and corrugated sheets produced by oorrugating the same flat thin sheets to impart therein waves of a pitch of am. 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 8, excepting the aforementioned metallic monolithic carrier was used in the place of the monolithic carrier of cordierite.

15 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 diameter of 4 microns and the rhodium-containing alumina in the form of particles possessing an average particle diameter of 3.5 microns.

This catalyst was found to contain 100 g of alumina, of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example 14 An aqieous slurry was obtained by wet pulverizing 139 g of the same activated alumina as used in Example 8 in a ball mill for 13 hours. Further an aqueous slurry for coating was obtained by wet pulverizing the aqueous slurry and the alumina powder containing 16.7% by weight of platinum and the alumina 'powder containing 9% by weight of rhodium prepared in Example 8 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 possessing an average particle diameter of 15 microns and the rhodium-containing alumina in the form of 26 particles possessing an average particle diemeter of 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 An Aqueous slurry was prepared by wet pulverizing 150 of an activated alumina possessing a specific surface area of 100 m 2 /g in a ball mill. The same monolithic carrier of cordierite as used in Example 8 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 sol,.tion contaiing 0.013 15 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, dried at 130°C for 3 hours, and then calcined in the air at 400 C for 2 hours, to obtain a finished catalyst.

When the coating layer of this catalyst was examined by EPMA, neigher platinum nor rhodium were found to be dispersed in the form of particles exceeding micron in diameter. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g i of rhodium per liter of the catalyst.

Control 6 j An alumina powder containing 35.7% by weight of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing g of platinum with 2.7 g of the same activated alumina as used in Control 5, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400C for 2 hours.

27 -7 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, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400*C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 8, using the platinum-containing alumina powder and the rhodium-containing alumina powder mentioned above and 146 g of the same activated alumina as used above instead, t* When the coating layer of this catalyst was 15 examined by EPMA, the platinum-containing alumina and 1 the rhodium-containing alumina were found to be *dispersed in the form of particles possessing an average particle diameter of 6.5 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 7 An aqueous slurry was prepared by wet pulverizing 139 g of activated alumina pellets possessing a specific surface area of 120 m /g in a ball mill for 19 hours.. An aqueous slurry for coating was obtained by wet pulverizing this aqueous slurry and the alumina powder containing 16.7% by weight of platinum and the alumina powder containing 9% by weight of rhodium both prepared as in Example 8 in a ball mill for 1 hour. A finished catalyst was obtained by following the procedure of Example 8, using this coating slurry.

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 possessing an average particle diameter of 40 microns.

28 This catalyst was found to containg 100 g of alumina, g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Control 8 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 of an activated alumina possessing a specific surface 2 area of 120 n drying the resultant mixture, and then calcining the dried mixture in the air at 400 0 C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 8, 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 Ishifuku Kinzoku Kogyo 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 contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example The catalysts of Examples 8 through 14 and the catalysts of Controls 5 through 8 were tested for catalytic property after aging 4 n the electorc furnace.

This aging in the electric furnace was performed by exposing a given catalyst to a high-temperature oxidative atmosphere involving ver: r harsh conditions of 10 hours' heating at 900°C.

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 ,o the exhaust system of the engine. The engine was "r,7ated, with the air 29 icombustion 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, the inlet gas temperature was continuously varied from 300'C to 500 0 The gas was sampled at the inlet and the outlet of the catalyst converter and analyzed to 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 obtained as described above as the functions of the inlet gas temperature were plotted on a graph to find Sthe inlet gas temperatures (T 0 showing a fixed purifying ratio of 50%. The inlet gas temperatures

(T

50 thus determined were used as the standard for evaluation of the purifying property of catalyst at low temperatures.

SThe results obtained by the method of evaluation of catalytic property described above are shown in Table e 30 i r V It 1 t Table 5 Evaluation of catalytic property after aging in electric furnace Purifying property at low temperatures CO purifying HC purifying NO purifying temperature, temperatue, temperature, Catalyst T 50

T

50

T

50 Example 8 395 399 393 9 410 414 408 402 408 400 11 400 404 397 12 398 404 396 13 393 398 390 14 398 405 397 Control 5 465 468 465 6 450 455 449 7 446 450 445 8 462 465 462 Then, the catalysts of Examples 8 through 14 and the catalysts of Controls 5 through 8 were tested 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 harsh conditions of a high-temperature oxidative atmosphere), with the catalyst exposed to 50 hours' aging under conditions such that the inlet gas temperature would reach 800'C during the steady operation.

Ar I Vt t VtP 31 k 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 furnace described above. The data consequently obtained were compared with those of the purifying property at low temperatures. The results are shown in Table 6 below.

Table 6 Evaluation of catalytic property after test run of engine n S*0 Purifying property at low temperatures 1 CO purifying HC purifying NO purifying temperature, temperature, temperature, Catalyst T 5 0

T

50 (oC) T 50

(C)

Example 8 375 380 369 9 388 394 380 385 392 376 11 379 385 370 12 377 385 369 13 373 380 365 14 378 386 370 Control 5 440 447 436 6 430 436 425 7 425 430. 420 8 440 446 436 It is clearly noted from Tables 5 and 6 that the catalysts of Examples 8 through 14 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 particles possesing an average particle diameter in the 32 range of 0.5 to 20 microns invariably exhibited better catalytic properties than the catalysts of Control which had noble metals dispersed in the conventional state. The catalyst of Control 6 which had platinum 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 7 which had platinum and rhodium deposited in ratios falling in the range specified by the present invention and but had these noble metals dispersed in the form of particles exceeding 30 microns in diameter, and the catalyst of Control 8 which had no platinum 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 udner harsh conditions as in a high-temperature oxidative atmosphere.

Exmaple 16 A finished catalyst was obtained by following the procedure of Example 8, excepting 75 g of a commercially available cerium oxide powder (produced by Nissan Kigenso 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 8, 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 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.

33 Example 17 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 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 400 0 C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 16, 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 16.

Stt, When the coating layer of this catalyst was o. 15 examined by the same method as in Example 8, 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 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 18 An alumina powder containing 1% by weight of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing g of platinum with 147 g of an activated alumina te, possessing a specific surface area of 120 m 2 drying the resultant mixture, and then calcining the dried mixture in the air at 400°C for 2 hours.

A finished catalyt was obtained by following the procedure of Example 16, excepting the platinum-containing alumina powder was used in the place of the alumina powder containing 16.7% by weight of platinum and the activated alumina used in Example 16.

34 When the coating layer of this catalyts was examined by the same method as in Example 8, the rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle 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.

Example 19 A finished catalyst was obtained by following the procedure of Example 16, excepting an aqueous platinic chloride solution was used in the place of the t aqueous solution of the nitrate of dinitro-diamine 15 platinum. The platinum-containing alumina used in this Scase 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 8, the platinum-containing alumina was found to be dispersed in 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 t 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 catalyst.

Example A finished catalyst was obtained by following the procedure of Example 16, excepting an aqueous rhodium 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 8, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle 35 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 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 catalyst.

Example 21 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 of aluminum nitrate [Al(N0 3 3 9H 2 0] with 319 g of cerium carbonate powder (possessing a Ce content of 47% by weight as Ce02), drying the resultant mixture at 4 130 0 C for *5 hours, and then calcining the dried mixture in the air at 500°C for 1 hour.

A finished catalyst was obtained by following 'the procedure of Example 16, 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 examined by the same method as in Example 8, the platinum-containing aluminum and the rhodium-containing alumina were both found to be dispersed in the form of 44, particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 100 g of alun,ina, alumina-modified cerium oxide (atomic ratio of SI Ce/Al 1.0 g of platinum, and 0.2 g of rhodium.

utt Example 22 9 t An alumina-toodified cerium oxide (atomic ratio of Ce/Al 8) was prepared by thoroughly mixing 220 ml of an aqueous solution having dissolved therein 54.4 g of aluminum nitrate [AI(NO3) 3 9H 2 0] with 426 g of cerium carbonate powder (possessing a Ce content of 47% by weight as Ce02), drying the resultant mixture at 130*C for S hours, and then calcining the dried mixture in the air at 500'C for 1 hour.

36 i U I r- ri A finished catalyst was obtained by following the procedure of Example 16, 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 8, 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 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al 1.0 g of platinum, and 0.2g of rhodium per liter of the catalyst.

m Example 23 T" 15 An alumina-modified cerium oxide (atomic ratio tit of Ce/Al 5) was prepared by mixing 94.7 g of alumina sol (containing 10% by weight as alumina 340 g of r cerim carbonate (possessing a Ce content of 47% by weight as CeO2), and 100 ml of water, drying the resultant mixture at 130°C for 5 hours, and then calcining the dried mixture in the air at 500 0 C for 1 hour.

A finished catall.t was obtained by following the procedure of Example 16, excepting 75 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 8, the Splatinum-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 microns. This catalyst was found to contain 100 g of alumina, 50 g of alumina-modified cerium oxide (atomic ratio of Ce/Al 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.

Example 24 37 I

J

t.t 4 6; *4 4 t A finished catalyst was obtained by following the procedure of Example 16, excepting he same metallic monolithic carrier as in Example 13 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 8, the platinum-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 4 microns and t "e rhodium-containing alumina 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.

Example An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 16 with 75 g of commnercialy availalbe cerium oxide in a ball mill for 13 hours, Further an aqueous slurry for 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 16 in a, ball mill for 7 holu'rs. A finished catalyst was obtained by following the procedure of Example 16, using the aqueous slurry for coating.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing alumina was found to be dispersed in 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 3.00 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 9 38 A catalyst was obtained by following the procedure of Example 5, excepting 75 g of a commercially available cerium oxide powder was incorporated in addition to 150 g of the same activated alumina as used in Example 16.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium 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, g of cerium oxide, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.

Control ,A finished catalyst was obtained by following 15 the procedure of Control 6, excepting 75 g of cerium S, oxide was further incorporated during the course of ,a mixture of the powder.

When the coating layer of this catalyst was examined by the same method as in Example 8, the 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 0.2 g of rhodium per liter of the catalyst.

Control 11 A finished catalyst was obtained by following the procedure of Control 7, excepting 75 g of cerium oxide was further incorporated during the course of mixture of the powders.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing 'alumina was found to be dispersed in the form of particles possessing an average particle 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 39 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 12 A finished catalyst was obtained by following the procedure of Control 8, excepting 75 g of cerium oxide was further incorporated during the mixture of the powders.

When the c ting layer of this catalyst was examined by the same method as in Example 8, platinum was found to be dispersed in the form of particles possess:ing an average particle diameter of 1 micron and no rhodium was found to be dispersed in the form of Sparticlee exceeding 0.5 micron in diameter. This S* 15 catalyst was found to contain 100 g of alumina, 50 9 of S cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium t per liter of the catalyst.

Exmaple 26 The catalysts of Examples 16 through 25 and the catalyts of Controls 9 through 12 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 15. The three way performance of each catalyst evaluated by the 4- 25 same engine as Example 8. The evaluation conditions were as follows: The catalyst inlet gas temperature was maintained at 450 C, and the space velocity was adjusted -1 to 90,000 hr The air-fuel ratio was changed 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, and NO purifying ratios of each catalyst were 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 40 7 r7 I I I ~I t~I~ Ii I at the crossing point between the CO purifying curve and the NO purifying curvc. The crossover point and the HC purifying ratiQ at the air-fuel ratio of the crossover point were used as the standard ifol- evaluation of the three way performance. The results aro respectively shown in Table 7 and Table P Table 7 Evaluation of catalytic property after aging in electric furnace Three way Purifying property at performance low temperatures______ C'ttalyst Crossover po-nt 0 purifyi, fC_ -purifying pu in g t emperature temperature temperature CO, tO -HC purify- purify- T 5 0 0 C) T 5 0 T 5 0 9C) irl ing ratio(,k) Bxamplel 88 87 386 390 385 171 80 81 403 407 400 18 83 83 395 400 392 19 87 86 388 393 386 20 89 88 385 388 383 21 94 96 370 375 366 22 93 94 373 377 370 23 91 94 375 379 373 24 89 8.1382 385 380 25 86 86 390 395 388 Control 9 .260 443 447 4441 63 68 427 430 426 11 65 72 420 425 J 418 12 49 58 445 449 4 44__ I 1-1 I I I 4<4 I II I I tIlt I I II 11111 41. 28

I

V

Table 8 Evaluation of catalytic property after test run of engine 1: **t rhree way Purifying property at oerformacne low tenperatures catalyst rossover p-int Co purifying HIC purifyingINO purifying temperature temperature Itemperature :ONO HC ?urify- purify- T 5 0 (OC) T so (OC) T 5 0 (0C) Lng ing ratio(% Examplel6j 87 93 356 360 350 17 80 90 365 370 360 18 83 9 6 6 191 86 93_38_36_35 87 93 37 36 21 94 98 340 345_____334_ 22 92 97_342346_33 23 93 97_344349_33 24_89_ 94_35 358 347 85 91 360 364 354 2ontrol 9 73 83 393 401. 390 75 85 393 400 389 11 77 86 332 +390 376 70 81 395 403 390 It is clearly noted the catalysts of Examples refractory inorganic oxidez from Tables 7 and 8 that 16 throuc having jh 25 in platinum which and/or rhodium deposited in high ratios as contemplated by the present invention Were dispersed in the f orm. of 'particles possessing an average particle diameter ip the range of 0. 5 to 20 microns invariably exhibited bt, catalytic property than the catalyst of Control 9 having the noble metals deposited and dispersed in the conventional states,~ The catalyst of Control 10 which had platinum deposited. in a ratio of not less than by,weight and rhodium in a ratio of not less. than 20% by 42 weight, the catalyst of Control 11 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, and the catalyst of Control 12 which had no platinum deposited on a refractory inorganic oxide invariably exhibited poor properties.

The catalysts of Examples 21 through 23 which used alumina-modified cerium oxide as a cerium oxide exhibited still better properties.

Example 27 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 specific surface area of 100 m /g with a mixture of an aqueous solution of the nitrate of dinitro-ammine platinum containing 1.5 q of platinum and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 40 0 °C 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 i 25 alumina powder in a ball mill for 20 hours. The same monolithic carrier as used in Example 8 was immersed in this aqueous slurry for coating, removed from the slurry, anr.; then blown with compressed air to remove excess slurry from within the cells and relieve all the cells of clogging slurry. Then, the wet carrier was calcined at 130°C for 3 hours, to obtain a finished catalyst.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average 43 I 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 13 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 27 with a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum and an aqueous rhodium nitrate solution, thoroughly drying the resultant mixture, and then calcining the dried mixture in the air at 400oC for 2 hours. A finished catalyst was obtained by following the procedure of Example 27, using the aforementioned alumina powder containing platinum and rhodium.

When the coating layer of this catalyst was L op o.o examined by the same method as in Example 8, the oaao platinum- and rhodium-containing alumina was not found to be dispersed in the form of particles exceeding 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.

.C'O Example 28 A finished catalyst was obtained by following 25 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 6 platinum. The platinum- and rhodium-containing alumina had 16.4% by weight of platinum and 3.1% by weight of p rhodium deposited thereon.

When the coating layer of this catalys' was examined by the same method as in Example 8, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average particle diameter of 7 microns. Th,3 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.

44 Example 29 A finished catalyst was obtained by following the procedure of Example 27, excepting an aqueous rhodium chloride solution was used in the palce of the 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 examined by the same method as in Example 8, 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 ti 15 g of rhodium per liter of the catalyst.

Example An alumina powder containing 11.4% by weight of platinu-m and 3.4% by weight of rhodium was prepared by mixing 7.5 g of an activated alumina possessing a specific surface area of 120 m2/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 re~rIltant mixture, and then calcining the dried mixture in the air at 400*C for 2 hours.

A finished catalyst was obtained by following the procedure of Exnaple 27, excepting the platinum- and rhodium-containing alumina was used in the place of the 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 particles possessing an average particle diamter of 45 h

_I~

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 31 A finished catalyst was obtained by following the procedure of Example 27, excepting the same metallic monolithic carrier as used in Example 13 was used in the place of the monolithic carrier of cordierite. The platinum- and rhodium-containing alumina used in this 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 8, the platinum- and rhodium-containing alumina was fo'nd to be 15 dispersed in the form of particles possessing an average particle diameter of 4 microns, This catalyst was found kt to contain 100 g of alumina, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example 32 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 27 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 16.1% by weight of platinum and 3.2% by weight of rhodium as in Example 27 in a ball mill for 7 hours. A finished catalyst was obtainid by following the procedure of Example 27, using the aqueous slurry for Scoating.

S 30 When the coating layer of the catalyst was examined by the same method as in Example 8, the ,platinum- and rhodium-containing alumina was found to be dispersed in the form of particles pcssessing an average particle diameter of 15 microns. This catalyst was found to contain 100 g of alumina, 1.0 g of platinum, and 0.2 of rhodium per liter of the catalyst.

Example 33 46 The catalysts of Examples 27 through 32 and the catalyst of Control 13 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in the same manner as in Example 15. The results are shown respectively in Table 9 and Table S47 7 I t 47 fly.

Table 9 Evaluation of catalytic property after aging in electric furnace r Purifying property at low temperatures Co purifying HC purifying NO purifying Catalyst temperature, temperature, temperature,

O

C) T 50

T

50 o

C)

Example 27 385 390 382 28 390 394 388 29 388 392 385 395 399 392 31 386 390 382 32 393 397 390 Control 13 465 468 465 Table 10 Evaluation of catalytic property after test run of engine Purifying property at low temperatures Co purifying HC purifying NO purifying Catalyst temperature, temperature, temperature, 0 c) T 50

T

50 (oC) Example 27 364 370 359 28 369 375 364 29 367 374 361 375 382 370 31 363 369 357 32 373 380 368 :ontrcl 13 440 447 436 48 t 6t 4 t 4 I~ It is clearly noted from Table 9 and Table that the catalysts of Examples 27 through 32 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios contemplated by this invention were dispersed in the form of particles possessing an average particle diameter in the range of 0.5 to microns exhibited far better catalytic properties than the catalyst of Control 13 having noble metals deposited in the conventional state.

Example 34 A finished catalyst was obtained by following the procedure of Example 27, excepting 75 g of a commercially available cerium oxide powder (produced by Nissan Kigenso was additionally used with 139 g of 15 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 8, 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 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.

25 Control 14 A finished catalyst was obtained by following the procedure of Example 34, excepting 75 g of the same commercially available cerium oxide powder as used in Example 34 was used in addition to the platinum- and rhodium-containing alumina powder obtained as in Control 13.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum n.or rhodium was found to be dispersed in the form uf particles exceeding 0.5 micron in diameter.

44: 4 4,, 49 This catalyst was found to contain 100 g of alumina, g of cerium oxide, 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example A finished catalyst was obtained by following the procedure of Example 34, 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 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 8, the platinum- and rhodium-containing alumina was found be 15 dispersed in the form of particles possessing an average 'lt" particle diameter of 7 microns. This catalyst was found S, 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 36 A finished catalyst was obtained by following the procedure of Example 34, excepting an aqueous rhodium chloride solution was used in the place of the aqueous rhodium nitrate solution. The platinum- and 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 8, 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 cohtain 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 37 50 :I c A finished catalyst wa. obtained by following the procedure of Example 34, excepting the same platinum- and rhodium-containing alumina as obtained in Example 30 was used in the place of the 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 8, 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, 50 g of cerium oxide, 0.67 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

15 Example 38 ,r t A finished catalyst was obtained by following the procedure of Example 34, excepting the same metallic monolithic carrier as in Example 13 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 8, 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 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 39 A finished catalyst was obtained by following the procedure of Example 34, excepting 75 g of the same alumina-modified cerium oxide as in Example 21 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 8, the platinum- and rhodium-containing alumina was found to be dispersed in the form of particles possessing an average 51 ~Y 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 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example A finished catalyst was obtained by following the procedure of Example 34, excepting 75 g of the same alumina-modified cerium oxide as in Example 22 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 8, the platinum- and rhodium-containing alumina was found to be S* 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 1.0 g of platinum, and 0.2 g of rhodium per liter of the 20 catalyst.

Example 41 4 44 A finished catalyst was obtained by following S the procedure of Example 34, excepting 75 g of the same alumina-modified cerium oxide as in Example 23 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 8, the platinum- and rhodium-containing alumina was found to be S* 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 a 1.0 g of platinum, and 0.2 g of rhodium per liter of the catalyst.

Example 42 52 An aqueous slurry was prepared by wet pulverizing 139 g of the same activated alumina as used in Example 34 and 75 g of a commercially available cerium oxide in a ball mill for 13 hours. An aqueous 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 34 in a ball mill for 7 hours. A finished catalyst was obtained by following the procedure of Example 34, using the aforementioned aqueous slurry for coating.

When the coating layer of this catalyst was examined by the same method as in Example 8, 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 43 The catalysts of Examples 34 through 42 and the catalyst of control 14 were tested for catalytic property after aging in an electric furnace and for i catalytic activity after endurance test in an engine in S, 25 the same manner as in Example 15. The results are shown in Table 11 and Table 12.

53

I

Table 11 Evaluation of catalytic property after aging in electric furnace 99

I

9 9* 91 9* 9 9 ~l 9 9* 9* 9 9*99 9949

I

*91 1 9* *4*1 Three way Purifying property at performance low tempratures -atalyst Crossover point Co Purifying HC purif-ying NO purifying temperacure temperature temperature CONo HC purify- purify- T 0 0 C) T 0 (OC) T 0

(OC)

ing Ing ratio(%) 'Example34 90 91 380 385 377 35 88 88 384 390 381 36 89 90 382 388 378 37 85 86 390 396 388 38 91 92 379 385 376 39 94 916 370 375 367 40 92 9 373 378 370 41 92 93 372 376 368 42 87 88 390 395 387 Controll4 51 60 443 447 441 4 W Table 12 Evalrnation of catalytic property after test run of engine Three way. Purifytng property at performance low temipratures Cfataly~st Crossover point' 0 purifying RC purifying NO purify Y__1 emp ert e teznperature temperature CO,NO HC purify- purify- T 0 0 C) T 5 (eC) T 0 0 c) ing ig5 05 ratio,(%)I Examplle34 90 95 1 348 35334___ 351 87 93 354 360 348 361 88 93 352 358 345 37 85 90 360 366 354 38 91 96 347 353 340 39 95 97 340 345 334 93 96 342 348 336 4.93 96 342 3475 S 42 .86 92 358 362 j 351 *,ontrol41 73 83 393 401 390 55 It is clearly noted from Table 11 and Table 12 that the catalysts of Examples 34 through 42 in which refractory inorganic oxides having platinum and rhodium deposited in high ratios a-j contemplated by the present invention were dispersed in the form of particles possessing an average particle diameter in the range of to 20 microns invariably exhibited better properties than the catalyst of Control 14 having noble metals deposited in the conventional state. Particularly the catalysts of Example 36 through 41 which used alumina-modified oxides as cerium oxide exhibited notable satisfactory properties.

Example 44 I A zirconia powder containing 16.7% by weight j 'i 15 of platinum was prepared by mixing an aqueous solution of the nitrate of dinitro-diammine platinum containing I 1.5 g of platinum with 7.5 g of zirconia possessing a specific surface area of 60 m2/g and an average particle diameter of 200 A (produced by Daiichi Kigenso Kagaku drying the resultant mixture overnight at 120 0

C,

and then calcining the dried mixture in the air at 400 0

C

for 2 hours.

A zi4rconia powder containing 9% by weight of rhodium was prepared by mixing an aqueous rhodium nitrate solution, containing 0.3 g of rhodium and 3 g of the same zirconia as mentioned above, drying the resultant mixture overnight at 120OC, and then calcining the dried mixture in the air at 400°C for 2 hours.

An aqueous slurry 'for coating was prepared by severally pulverizing the platinum-contaning zirconia powder and rhodium-containing zirconia powder in a mortar until an average particle diameter of about microns, mixing the pulverized powders with 130 g of an activated alumina possessing a specific surface area of 100 m 2 and wet pulverizing the resultant mixture in a ball mill for 20 hours.

56 A finished catalyst was obtained by immersing the same monolithic carrier as used in Example 8 in the coating aqueous slurry, removing the carrier from the slurry, blowing the wet carrier with compressed air so as to relieve all the cells in the carrier of clogging ,slurry, end then drying the carrier at 130 0 C for 3 hours.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particles possessing an equal average particle diameter of 7 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per' carrier piece.

S 15 Example S> A zirconia powder containing 16.7% by weight of palladium was prepared by mixing an aqueous palladium nitrate solution containing 1.5g of palladium with 7.5 g of the same zirconia as used in Example 44, drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 400 0 C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 44, excepting the palladium-containing zirconia powder was used in the place of the platinum-containing zirconia powder.

When the coating layer of this catalyst was examined by the same method as in Example 8, the palladium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns and the rhodium-containing .A zirconia in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 0.065 g of palladium and 0.013 g of rhodium per carrier piece.

Example 46 57 A zirconia powder containing 5% by weight of palladium was prepared by mixing 7.5 g of the same zirconia as used in Example 44 with a mixture of an aqueous platinic chloride solution containing 0.9 g of platinum and an aqueous palladium chloride solution containing 0.6 g of palladium, drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 400°C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 44, excepting the platinum- and palladium-containing zirconia poider was used in the place of the platinum-containing zirconia powder.

When the coating layer of the catalyst was S, examined by the same method as in Example 8, the 15 platinum- and palladium-c'ntaining zirconia was found to be dispersed in the form of particles possessing an Saverage particle diameter of 13 microns and the rhodium-containing zirconia in the form of particles possessing an average particle diameter of 5 microns.

This catalyst was found to contain 0.039g of platinum, 0.026 g of palladium, and 0.013 g of rhodium per carrier piece.

Example 47 A finished catalyst was obtained by followig the procedure of Example 44, excepting a zirconia possessing a specific surface area of 90 m 2 /g and an average particle diameter of 150 A (produced by Daiichi Kigenso Kagaku was used in the place of the zirconia of Example 44 When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 2 microns and the rhodium-containing zirconia in the form of particles possessing an average 58 r~l particle diameter of 6 microns. This catalyst was found to contain 0.065 g platinum and 0.013 g of rhodium per carrier piece.

Example 48 A finished catalyst was obtained by following the procedure of Example 44, excepting the same metallic monolithic carrier as used in Example 13 was used in the place of the monolithic carrier of cordierite of Example 44.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia was found to be dispe?:sed in the form of particles possessing an average particle diameter of 6 microns and the rhodium-containing 15 zirconia in the form of particles possessing an average particle diameter of 7 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 49 An alumina powder containing CeO 2 and Fe 2 0 3 was obtained by dissolving 25.2 g of cerium nitate CCe(NO3) 3 6H 2 0] and 10.1 g of ferric nitrate [Fe(N0 3 3 9H 2 0] in 100 g of purified water, mixing the resultant aqueous solution with 127 g of an activated alumina possessing a specific surface area of 100 m 2 drying the resultant mixture overnight at 120°C, and then calcining the dried mixture in the air at 700 0 C for 1 hour.

A finished catalyst was obtained by following the procedure of Example 44, excepting the CeO 2 and 3 -containing alumina was used in the place of 139 g of the activated alumina of Example 44 When the coating layer of this catalyst was examined by the same method as in Exmaple 8, the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed in the form of 59 e 1 particles possessing an equal average particle diameter of 5 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 of rhodium per carrier piece.

Control, An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same activated alumina possessing a specific surface area of 100 m2/g as in Example 44.

A finished catalyst was obtained by coating the same monolithic carrier of cordierite as in Exampl! S44 with 6.5 g as alumina of the aqueous slurry for coating, immersing the carrier coated with the activated alumina in a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum, and an aqueous 15 solution of rhodium nitrate,removing the carrier from the solution, blowing the wet carrier wit.i compressed Sair to remove excess aqueous solution, drying the wet carrier at 130°C for 3 hours, and calcining the dried carrier in the air at 400°C for 2 hours.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither i'i platinum 'nor rhodium was found to be dispersed in the I| form of particles exceeding 0.5 micron in diameter.

i This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Control 16 K An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same zirconia possessing a specific surface area of 60 m 2 /g and an average particle diameter of 200 A as in Example 44.

SA finished catalyst was obtained by coating the same monolithic carrier of cordierite as in Example 44 with 6.5 as zirconia of the aqueous slurry for coating and depositing platinum and rhodium on the carrier coated with zirconia by following the procedure of Control 60 When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.

This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diamter. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

The catalysts of Examples 44 through 49 and 15 the catalysts of Controls 15 and 16 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in the same manner as in Example 15. The results are shown in Table 13 and Table 14.

61

I?

Table 13 Evaluation of catalytic property after aging in electric furnace Ir tIl fit Purifying pro erty at low temperatures CO purifying HC purifying NO purifying Catalyst temperature, temperature, temperature, o C) T50 T50 (C) Example 44 383 388 381 375 381 374 46 377 384 375 47 381 386 379 48 380 386 378 49 378 385 375 Control 15 456 460 455 16 463 468 462 Table 14 Evaluation of catalytic property after test run of engine Purifying property at low temperatures CO purifying HC purifying NO purifying Catalyst temperature, Imperature, temperature, T50 OC) T50

O

C)

Example 44 360 366 352 375 382 369 46 370 376 365 47 361 365 353 48 358 363 350 49 362 368 354 Control 15 438 455 453 16 442 450 440 62 Example 51 A finished catalyst was obtained by following Sthe procedure of Example 44, excepting 75 g of a commercially available cerium oxide powder (produced by Nissan Kidogenso was used in addition to the platinum-containing zirconia powder, rhodium-containing zirconia powder, and 139 g of the activated alumina of Example 44. When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particles possessing an average particle diameter of 7 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

15 Example 52 S1 m A zirconia powder containing 16.7% by weight of palladium was prepared by mixing an aqueous palladium nitrate solution containing 1.5 g of palladium with g of the same zirconia as used in Example 51, drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 400°C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 51, excepting the palladium-containing zirconia powder was used in the place of the platinum-containing zirconia powder of Example 51. When the coating layer of this catalyst was examined by the same method as in Example 8, the palladium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns and the rhodium-containing zirconia in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 0.065 g of palladium and 0.013 g of rhodium per carrier piece.

Example 53 63 *ie i A zirconia powder containing 10% by weight of platinum and 6.7% by weight of palladium was prepared by mixing 7.5 g of the same zirconia as used in Example 51 with a mixture of an aqueous platinic chloride solution containing 0.9 g of platinum and an aqueous palladium chloride solution containing 0.6 g of palladium, drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 400°C for 2 hours.

A finished catalyst was obtained by following the procedure of Example '51, excepting the platinum- and palladium-containing zirconia powder was used in the place of platinum-containing zirconia powder of Example 51.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and palladium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 13 microns and the rhodium-containing zirconia in the form of particles possessing an average particle diameter of 5 microns.

This catalyst was found to contain 0.039 g of platinum, 0.026 g of palladium, and 0.013 g of rhodium per catalyst piece.

Example.5.4 A finished catalyst was obtained by following the procedure of Example 51, excepting a zirconia possessing' a specific surface area of 90m /g and an average particle diameter of 150 A (produced by Daiichi Kigenso Kagaku was used in the place of zirconia of Example 51.

When the coating layer of this catalyst was examined by the same method as in Example 8. The platinum-containing zirconia was found to be dispersed in the form of particles possessing an average particle 64 I -P U r diameter of 0.5 micron and the rhodium-containing z.rconia in the form of particles possessing an average particle diameter of 1 micron.

Example A finished catalyst was obtained by following the procedure of Example 51, excepting the same metallic monolithic carrier as used in Example 13 was used in the place of the monolithic carrier of cordierite of Example 51.

When the coating layer of this catalyst \ss examined by the same method as in Example 8, the platinum-containing zirconia wa", found to be dispersed in the form of particles possessing an average particle j diameter of 6 microns and the rhodium-containing 15 zirconia in the form of particles possessing an average i particle diameter of 7 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 56 An alumina powder containing CeO 2 and Fe 2 0 3 was obtained by dissolving 25.2 g of cerium nitrate V (Ce(N0 3 3 6H 2 0) and 10.1 g of ferric nitrate (Fe(N0 3 3 9H20) in 100 g of purified water, mixing the resultant solution with 127 g of an activated alumina possessing a specific surface area of 100 m 2 drying the resultant mixture overnight at 120*C, and then calcining the dried mixture in the air at 7000C for 1 hour.

A finished catalyst was obtained by following the procedure of Example 51, excepting the alumina containing CeO 2 and Fe 2 0 3 was used in the place of 139 g 6of the activated alumina of Example 51.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia and the rhodium- zontaining zirconia were found to be dispersed both in the form of 65 particles possessing an average particle diameter of microns. .This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 57 A finished catalyst was obtained by following the procedure of Example 51, excepting 75 g of the same alumina-,modified cerium oxide as in Example 21 was used in the place of the commercially available cerium oxide powder of Example 51.

When the coating layer of this catalyst was examined by the same method as in Example 8f the tiame platinum-containing :irconia and the rhodium-containing zirconia were found to bo dispersed both in the form of particles possessing an equal average particle diameter of 3 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 58 A finished catalyst was obtained by following the procedure of Example 51, excepting 75 g of the same alumina-modified cerium oxide as in Example 22 was used in the place of the commercially available cerium oxide powder of Example 51.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing ziroonia and the rhodium-containing zircorti4a were found to be dispersed both in the form of p i eS p ~ing an equal average particle diameter of 6 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 59 A finished catalyst was obtained by following the procedure of Example 51, excepting 75 g of the same alumina-modified cerium oxide as in Example 23 was used in the place of the commercially available cerium oxide powder of Example 51.

66 i When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particles possessing an equal average particle diameter of 1 micron. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Control 17 An aqueous slurry for coating was prepared by wet pulverizing 150 g cf the same activated alumina possessing a specific surface area of 100 m2/g as used in Example 51 and 75 g of a commercially available cerium oxide powder in a ball mill for 20 hours.

,A finished catalyst was obtained by coating S 15 the same monolithic carrier of cordierite as obtained in Example 51 with the aqueous slurry for coating, immersing the carrier coated with the activated alumina and the cerium oxide in a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum and an aqueous rhodium nitrate solution, removing the carrier from the mixture, blown with compressed air to remove excess solution, drying the wet carrier at 130 0 C for 3 hours, and then calcining the dried carrier in the air at 400 0 C for 2 hours.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Control 18 An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same zirconia possessing a specific surface area of 60 m 2 /g and an average particle 0 diameter of 200 A and 75 g of a commercially available cerium oxide powder in a ball mill for 20 hours.

67 ~i~rn A finished catalyst was obtained by coating Sthe same monolithic carrier of cordierite as used in Example 51 with the aqueous slurry for coating and depositing platinum and rhodium on the carrier coated with zirconia and cerium oxide by following the procedure of Control 17.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.

This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium.

Example .°The catalysts of Examples 51 through 59 and 15 the catalysts of Controls 17 and 18 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in the same manner as in Example 15. The results are shown in Tables 15 and 16.

4i 68 Table 15 Evaluation of catalytic property after aging in electric fvirnace

I

atalyst Three way performance Purifying property at low temperatures.

atalstCros sover point fCO purifying HG purfyn f O urifying [temperature Itemperatr temerature

NO

Purif Yi ng ,a tio C%)

HC

purif ying ratio T 5 0 0

C)I

T 5 0 C)

I

T50 -C) l.a a a.

sea.

4 Ct a a a 1.~ a a £4 4 t ExampleSlJ 88 89 380 385 377 52 90 91 j 374 380 370 53 88 90 378 384 375 54 87 89 I 381 385 376 55 88 90 377 381 374 56 86 88 385 390 382 57 93 94 367 372 365 58 92 93 ___39373 365 59 91 93 370 375 367 "ontro.117 61 66 445 449 443 18 58 63 450 455 448_ 69 i Table 16 Evaluation of catalytic property after test run of engine t 0t Three way Purifying property at performance low temperatures Catalyst Crossover point CO purifying HC purifying NO purifying temperature temperature temperature CO,NO

HC

purify- purify- T50 T 5 0 50 ing ing ratio(%) ratio(%)_ Example51 86 92 355 360 349 52 83 90 365 372 360 53 85 92 362 370 355 54 86 93 352 358 345 87 93 356 362 349 56 88 94 353 359 345 57. 94 98 340 345 333 58 92 97 344 350 336 59 92 96 343 348 335 Controll7 70 81 395 402 390 18 65' 76 401 410 395 It is clearly noted from Tables 15 and 16 that the catalysts of .Examples 51 through 59 in which zirconia powders having platinum, palladium,and rhodium deposited in high ratios contemplated by the present invention were dispersed in coating layers in the form of coherent particles possessing an average particle diameter in the range of 0.5 to 20 microns invariably exhibited better catalytic properties than the catalysts of Controls 17 and 18. The catalysts of Examples 57 through 59 which used alumina-modified cerium oxides exhibited still better properties.

Example 61 A zirconia powder containing 16.1% by weight of platinum and 3.2% by weight of rhodium was prepared by mixing 7.5 g of a, zirconia possessing a specific surface area of 60 m2/g and an average particle diameter 70

I~_

of 200 A (produced by Daiichi Kigenso Kagaku with a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum containing 1.5 g of platinum and an aqueous rhodium nitrate solution containing 0.3 g of rhodiumdrying the resultant mixture overnight at 120°C, and then calcining the dried nmixture in the air at 400°C for 2 hours.

An aqueous slurry for coating was prepared by pulverizing the platinum- and rhodium-containing zirconia powder in a mortar until coherent particles possessing an average particle diameter of about microns were formed, mixing the pulverized powder with 139 g of an activated alumina possessing a specific surface area of 100 m 2 and wet pulverizing the 15 resultant mixture in a ball mill for 20 hours.

S. A finished catalyst was obtained by immersing the same monolithic carrier as used in Example 8 in the aqueous slurry for coating, removing the carrier from the slurry, blowing the wet carrier with compressed air to relive al'l the cells of the carrier of clogging slurry, and drying the coated carrier at 130 0 C for 3 hours.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter 7 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 62 A zirconia powder containing 16.1% by weight of palladium and 3.2% by weight of rhodium was prepared by mixing 7.5 g of the same zirconia as used in Example 1 with a mixture of an aqueous palladium nitrate solution containing 1.5 g of palladium and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, 71 LI ~rwu~ drying the resultant mixture overnight at 120°C, and then calcining the dried mixture in the air at 40 0 °C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 61, excepting the palladiumand rhodium-containing zirconia powder was used in the place of the platinum- and rhodium-containing zirconia powder of Example 61.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 3 microns. This catalyst f o\ was found to contain 0.065 g of palladium and 0.013 g of i 15 rhodium.

S« Example 63 A zirconia powder containing 9.7% by weight of platinum, 6.5% by weight of palladium,and 3.2% by weight of rhodium was prepared by mixing 7.5 g of the same zirconia as used in Example 61 with a mixture of an aqueous platinic chloride solution containing 0.9 g of platinum, and aqueous palladium chloride solution containing 0.6 g of palladium,and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 400 0 C for 2 hours.

A finished catalyst was obtained by following the procedure of Example 61, excepting the platinum-, palladium-, and rhodium-containing zirconia powder were used in the place of platinum- and rhodium-containing zirconia of Example 61.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-, palladium-, and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 13 microns.

72

L-~

lr This catalyst was found to contain 0.093 g of platinum, 0.026 g of palladium, and 0.013 g of rhodium per carrier piece.

Example 64 A finished catalyst was obtined by following the procedure of Example 61, excepting a zirconia possessing a specific surface area of 90 m2/g and an average particle diameter of 150 A (produced by Daiichi Kigenso Kagaku was used in the place of the zirconia of Example 61.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 2 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Exmaple A finished catalyst was obtained by following the procedure of Example 61, excepting the same metallic carrier as used in Example 13 was used in the place of the monolithic carrier of cordierite of Example 61.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier p 4 ece.

Example 66 An alumina powder containing CeO 2 and Fe203 was obtained by dissolving 25.2 g of cerium nitrate (Ce(N0 3 3 6H 2 0) and 10.1 g of ferric nitrate (Fe(NO 3 3 in 100 g of purified water, mixing the resultant solution with 1V5 g of an activated alumina possessing 73 2 a specific surface area of 100 m drying the resultant mixture overnight at 120 0 C, and then calcining the dried mixture in the air at 700 0 C for 1 hour.

A finished catalyst was obtained by following the procedure of Example 61, excepting the CeO 2 and Fe 2 0 3 containing alumina was used in the place of 139 g of the activated alumina of Example 61.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. This catalsyt was found to contain 0.065 g of platinum and 0.013 g of S, rhodium per carrier piece.

S 15 Control 19 An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same activated alumina 2 possessing a specific surface area of 100 m /g as used in Example 61 in a ball mill for 20 hours.

A finished catalyst was obtained by coating the same monolithic carrier of cordierite with 6.5 g as alumina of the aqueous slurry for plating in the same manner as in Example 61, immersing the carrier coated

ZI

with the activated alumina in a mixture of an aqueous S 25 solution of the: nitrate of dinitro-diammine platinum and an aqueous rhodium nitrate solution, removing the carrier from the mixture, blowing the wet carrier with compressed air to remove excess aqueous solution, drying oo the wet carrier at 130 0 C for 3 hour;s and calcining the dried carrier in the air at 400°C for 2 hours.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.

This catalyt was found to contain 0.065 g of platinum and 0.013 g of rhodium per c;rrier piece., Control 74 An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same zirconia possessing a specific surface area of 60 m2 /g and an average particle

O

diameter of 200 A as used in Example 61 in a ball mill for 2 hours.

A finished catalyst was obtained by coating a monolithic carrier of cordierite with 6.5 g as zirconia of the aqueous slurry for coating in the same manner as in Example 61 and depositing platinum and rhodium on the carrier coated with the zirconia in the same manner as in Control 19.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the j 15 form of particles exceeing 0.5 micron in diameter. This jl catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 67 The catalysts of Examples 61 through 66 and the catalysts of Controls 19 and 20 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in L& engine in the same manner as in Example 15. The results i are shown in Table 17 and Table 18.

75 Table 1.7 Evaluation of catalytic property after aging in electric furnace I Purifying property ac low temperatures ~~1 CO purifying temperature, 50 0

C

IIC purifying ternperatue, T 50(

C)

NO purifying temperature, T 50 0 c) Catalyst 9* 4 4 44 9,94 9 4~ 94 9 9,99

I

*9.99

I

'9*9*9 I S 9 .9 '9 9 4 44 44 9 9 9 49 44949 4 9 '4.9$ a 9$ .4 4 9449? 4 9 4 Example 61 375 381 372 62 370 376 368 63 372 378 370 64 374 380 372 373 379 372 66 376 382 372 Control 19 456 460 455 20 463 468 462 Table 18 Evaluation of catalytic property after test run of engine Purifying property at' low temperatures CO purifying HC purifying NO purifying temperaturaI temperatue, temperature, Catalyst T 5 0 0 c) T 5 0 0 C) T so 0

C)

Example 61 354 360 347 62 36 5 372 359 63 363 370 3 5*6 64 355 360 347 352 358 344 66 355 361 347 Control 19 438 445 435 442 450 440 76 It is clearly noted from Table 17 and Table 18 that the catalyst of Examples 61 through 66 in which zirconia powders having platinum, palladium, and rhodium depozited in .high ratios contemplated by this invention disposed in the coating layers in the form of particles possessing an average particle diamter in the range of 0.1 to 20 microns invariably exhibited better catalystic properties than the catalysts of Controls 19 and which had noble metals deposited in the conventional state.

Example 68 A finished catalyst was obtained by following the procedure of Example 61 excepting 75 g of a commercially available cerium oxide (produced by Nissa o, ~15 Kidogenso was used in addition to the platinumand rhodium-containing zirconia powder and 139 g of the activated alumina of Example 61. When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 7 microns.

This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 69 A zirconia powder con %'ining 16.1% by weight of palladium and 3.2% by weight of rhodium was prepared by mixing 7.5 g of the same zirconia as used in Example 68 with a mixture of an aqueous palladium nitrate solution containing 1.5 g of palladium and an aqueous rhodium nitrate solution containing 0.3 g of rhodium, drying the resultant mixture overnight at 120 0 C, then calcining the dried mixture in the air at 400 0 C for 2 hours.

77-

MMPF__

A finished catalyst was obtained by following the procedure of Exmaple 68, excepting the palladiumand rhodium-containing zirconia powder was used in the place of platinum- and rhodium-containing zirconia powder of Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 9, the palladium- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 3 microns. This catalyst was found to contain 0.065 g of palladium and 0.013g of rhodium per carrier piece.

Example SA zirconia powder containing 9.7% by weight of S* 15 platinum, 6.5% by weight of palladium, and 3.2% by weight of rhodium was prepared by mixing 7.5 g of the S same zirconia as used in Example 68 with a mixture of an aqueous platinic chloride solution containing 0.9 g of platinum, an aqueous palladium chloride solution containing 0.6 g of palladium, and an aqueous rhodium nitrate solution containing 0,3 g of rhodium, drying the resultant mixture overnight at 120°C, and then calcining the dried mixture in the air at 400 0 C for 2 hours.

A finished catalyst was obtained by following 25 the procedure of Example 68, excepting the platinum-, palladium-, and rhodium-containing zirconia powder was used in the place of the platinum- and rhodium-containing zirconia powder of Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum-, palladium, and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 13 microns.

This catalyst was found to contain 0.039 g of platinum, 0.026 g of palladium, and 0.013 g of rhodium per carrier piece.

Exmaple 71 78 A finished catalyst was obtained by following the procedure of Example 68, excepting a zirconia 2 possessing a specific surface area of 90 m2/g and an average particle diamter of 150 A (produced by Daiichi Kigenso Kagaku was used in the place of the zirconia of Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 2 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g rhodium per carrier piece.

oa Example 72 A finished catalyst was obtained by following the procedure of Example 68, excepting the sama metallic #Ott monolithic carrier as used in Example 18 was used in the place of the monolithic carrier of cordierite of Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 8, the platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 6 microns. m's atalyst was found to contain 4.065 g of platinum A 0Uc 3 g of rhodium per carrier piece.

Example 73 An alumina powder containing CeO 2 and Fe 2 3 was obtained by dissolving 25.2 g of cerium nitrate (Ce(NO 3 3 6H 2 0) and 10.1 g of ferric nitrate (Fe(NO 3 9H 2 0) in 100 g of purified water, mixing the resultant solution with 127 g of an activated alumina possessing a specific surface area of 100m 2 drying the resultant mixture overnight at 120*C, and then a4ol ning the dried mixture in the air at 700"C for 1 hour.

79 A finished catalyst was obtained by following the procedure of Example 65, excepting the CeO 2 and Fe 2 0 3 -containing alumina was used in the place of 139 g of the activated alumina of Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 8, the same platinum- and rhodium-containing zirconia was found to be dispersed in the form of particles possessing an average particle diameter of 5 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium.

Fxample 74 A finished catalyst was obtained by following the procedure of Example 68, excepting 75 g of the same S 15 alumina-modified cerium oxide as in Example 21 was used S, in the place of the commercially available cerium oxide used in Example 68.

When the coating layer of this catalyst was examined by the same method as in Example 8, the same platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particles possessing an equal average particle diameter of 3 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example A finished catalyst was obtained by following the procedure of Example 68, excepting 75 g of the same alumina-modified cerium oxide as in Example 22 was used in the place of the commercially availabble cerium oxide powder used in Example 68.

When the coating layer of the catalyst was examined by,. the same ,method _as _in Example 8; the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particle possessing an c a1al average particle diameter of 1 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

80 i- Example 76 ,A finished catalyst was obtained by following the pr .dure of Example 68, excepting 75 g of the same alumina-modified cerium oxide as in Example 23 was used in the place of the commercially availabble cerium oxide powder used in Example 68.

When the coating layer of the catalyst was examined by the same method as in Example 8, the platinum-containing zirconia and the rhodium-containing zirconia were found to be dispersed both in the form of particle possessing an eqial average particle diameter of 1 microns. This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Control 2.1 An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same activated alumina 2 possessing a specific surface area of 100 m /g as used in Example 68 and 75 g of a commercially avilable cerium oxide powder in a ball mill for 20 hours.

A finished catalyst was obtained by coating a monolithic carrier of cordierite with the aqueous slurry for coating in the same manner as in Example 68, immersing the carrier coated with the activated alumina and the cerium oxide in a mixture of an aqueous solution of the nitrate of dinitro-diammine platinum and an aqueous rhodium nitrate soltuion, removing the carrier from the mixture, blowing the carrier with compressed air tc remove excess solution, drying the wet carrier at 130°C for 3 hours, and then calcining the dried carrier in the air at 400°C for 2 hours.

When the coating layer of this catalyst was Sexamined by the same method as in Example 8, neither platinum nor rhodium was found to be dispersed in the form of particles exceeding 0.5 micron in diameter.

This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Control 22 81 An aqueous slurry for coating was prepared by wet pulverizing 150 g of the same zirconia possessing specific surface area of 60 m2/g and an average particle diameter of 200 A as used in Example 68 and 75 g a commercially available cerium oxide powder in a ball mill for 20 hours.

A finished catalyst was obtained by coating a monolithic carrier of cordierite with the aqueous slurry for coating in the same manner as in Example 68 and depositing platinum and rhodium on the carrier coated with the zirconia and the cerium oxide in the same manner as in Control 21.

When the coating layer of this catalyst was examined by the same method as in Example 8, neither 15 platinum nor rhodium was found to be dispersed in the S form of particles exceeding 0.5 micron in diameter.

This catalyst was found to contain 0.065 g of platinum and 0.013 g of rhodium per carrier piece.

Example 77 The catalysts of Examples 68 through 76 and the catalyts of Controls 21 and 22 were tested for catalytic property after aging in an electric furnace and for catalytic activity after endurance test in an engine in the same manner as in Example 15. The results are shown in Table 19 and d e 6 L 82 Table 19 af ter Evaluation of catalytic property aging in electric furnace 1 4 4 Thre wayPurifying property at oerformance low tern ratures Catalyst Crossover point CO purif yingH C purifying NO purifying _______temperature temperature Itemperature purify- purify- T 5 0 (OC) T 5 0 (11C) T 5 0 0

C)

ratio(%) ratio(%) Ex~ue8 90 91 375 380 372 69 91 93 370 376 367 90 92 374 380 370 71 88 90 377 381 374 72 89 91 372 377 369 73 87 88 380 386 377 74 95 96 361 366 356 93 95 363 368 359 76 93 94 362 368 357 Iontrol2l 61 66 445 449 443 58 63 450 455 448 83 o~.

1

I

Table 20 Evaluation of catalytic property after test run of engine cr QD C *r C. ar Cf C *i

SC

C C Ce C I C 4* C C CI C C C Three way Purifying property at performance low tenpratures Catalyst Crossover point CO purifying HC purifying NO purifying temperature temperature temperature CO,NO HC purify- purify- T50 (OC) T 50

T

5 0 ing ing ratio(%) ratio(%) Example68 88 94 347 352 340 69 85 91 358 365 350 70 87 93 353 360 344 71 88 94 343 350 335 72 89 95 346 353 340 73 89 94 343 349 336 74 96 98 338 344 330 75 94 97 342 348 335 76 '94 97 341 346 334 Control21 70 81. 395 402 390 22 65 76 401 410 395 It is clearly noted from Table 19 and Table that the catalysts of Examples 68 through 76 in which zirconia powders having platinum, palladium, and rhodium deposited in high ratios as contemplated by the present invention were dispersed in the coating layers in the form of coherent particles having an average particle diameter in the range of 0.5 to 20 microns invariably exhibited very satisfactory catlytic properties as compared with the catalyst of Controls 21 and 22 which had noble metals deposited in the conventional state.

The catalysts of Examples 74 through 76 which used alumina-modified cerium oxides exhibited still better catalytic properties.

84 8: I- From the results given above, it is clear that the catalysts of the present invention incur only slight deterioration and possess outstanding durability under ordinary operating conditions of engine and even under harsh conditions as under a high-temperature oxidative atmosphere.

The claims form part of the disclosure of this specification.

85

Claims (11)

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 a platinum group metal-supporting zirconia produced by depositing said platinum group metal on zirconia powder, a refractory inorganic oxide, and a rare earth metal oxide, said platinum group metal is at least one Imember selected from the group consisting of rhodium, (b) combination of rhodium and platinum, combination of rhodium and palladium, and 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. I t

2. A catalyst according to claim 1, wherein said zirconia powder has a specific surface area of at least 10 m 2 /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 2C 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. j

5. A catalyst according to claim 1, wherein said I tt 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. S*

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 Scontaining a platinum group metal-carrying zirconia, f 1 A refractory inorganic oxide, and a rare earth metal oxide and amspe.004/nippon 90 8 87 calcining the resultant coated carrier, said platinum group metal is at least one member selected from the group consisting of rhodium, combination of rhodium and platinum, 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.

A catalyst for purifying exhaust gas, substantially as hereinbefore described with reference to any one of the specific Examples.

11. A method for the production of a catalyst S' substantially as hereinbefore described with reference to any S,,ft one of the specific Examples. Stt DATED this 20 August 1990 SMITH SHELSTON BEADLE Fellows Institute of Patent Attorneys of Australia Patent Attorneys for the Applicant: NIPPON SHOKUBAI KAGAKU KOGYO CO., LTD. amspe.004/nippon 90 8