JPS63190642A - Exhaust gas purification catalysts - Google Patents

Abstract

PURPOSE:To obtain the subject highly durable catalysts by permitting a honeycomb carrier of monolithic structure to support a catalytic composition containing zirconia which supports a specific amount of precious metal such as Pt and has particles with an average diameter of 0.5-20mum and a cerium oxide. CONSTITUTION:An aqueous slurry is prepared which contains (a) flocculated particles of pulverized zirconia permitted to support 5-30wt.% of platinum and/or palladium and/or pulverized zirconia to support 1-20wt.% of rhodium, each reduced to an average particle diameter of 0.5-20mum and (b) a cerium oxide which exists as a cerium dioxide in a catalyst. This slurry applied by washing to a honeycomb carrier of monolithic structure and dried to obtain exhaust gas purification catalysts. Catalysts of higher properties can be obtained by using water-insoluble cerium compound and water-soluble aluminum compound and/or alumina-denatured cerium oxide obtained from alumina hydrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst for purifying exhaust gas. Specifically, the present invention deals with hydrocarbons (HC), which are harmful components contained in exhaust gas from internal combustion engines such as automobiles,
- relates to an exhaust gas purification catalyst that simultaneously removes carbon oxides (co) and nitrogen oxides (NOx);
In particular, the present invention relates to an exhaust gas purifying catalyst that has excellent durability when used under severe conditions such as high-temperature oxidizing atmospheres, and has high purification performance at low temperatures against the above-mentioned harmful components.

[Conventional technology 1] Conventionally, in exhaust gas purification catalysts, efforts have been made to support precious metals as highly dispersed as possible on, for example, activated alumina with a high surface area, in order to effectively use precious metals whose use is limited to a small amount. has been done. However, although catalysts with highly dispersed noble metals supported have high initial activity, when exposed to harsh conditions such as high-temperature oxidizing atmospheres, noble metal particles are likely to grow and reactions between the noble metal and the support material occur. Since the precious metal is supported in a highly dispersed manner, there is a problem in that the activity deteriorates rather significantly.

In this field, zirconia is often used for the purpose of stabilizing physical properties such as the specific surface area of catalysts.
No. 29215 and Japanese Unexamined Patent Publication No. 57-153737 propose a method in which a coating layer containing alumina and zirconia is formed on a support and then a noble metal is supported.

However, in these methods, since most of the noble metals are substantially highly dispersed in alumina, activity deterioration occurs due to the same causes as described above.

U.S. Pat. No. 4,233,189 discloses a catalyst in which rhodium is supported at a low loading rate on zirconia after forming a coating layer of zirconia on a carrier, but the noble metal disclosed in the present invention is supported at a high loading rate on zirconia. The durability of the catalyst was significantly inferior compared to catalysts in which a small amount of supported zirconia was dispersed in other refractory inorganic oxides.

[Means for Solving the Problems] As a result of intensive research, the present inventors have found that the precious metals used are limited to shodai, which can be supported at a low loading rate on the refractory inorganic oxide with a high surface area between the rows. However, contrary to the conventional knowledge that the degree of dispersion of precious metals should be increased as much as possible, zirconia with a precious metal 3, which is a small amount of zirconia whose physical properties have been specified, is supported at a high loading rate, and its average particle size is 0. It was discovered that the durability of the catalyst could be dramatically improved by adjusting the agglomerated particles to relatively large sizes of 5 to 20 microns and dispersing them in the catalyst coating layer, which led to the completion of the present invention. .

[Structure of the invention] The configuration of the present invention will be explained in detail below.

First, the range of high loading of precious metals on zirconia is 5-30% for platinum and/or palladium.
, preferably 10-20% by weight, for rhodium 1
-20% by weight, preferably 1-10% by weight. If the platinum and/or palladium content is less than 51w% or the rhodium content is less than 1ww%, the state will be close to the normal high dispersion state (and the activity deterioration will be large). 20% by weight of rhodium
If it exceeds this, the number of active sites of negative metals that effectively contribute to the reaction will not increase, but will instead be reduced from the beginning (as a result, the initial performance of the catalyst will be low, and if the loading ratio is within the range of the present invention, the number of negative metal active sites will not increase. This causes the precious metal particles to grow, making the particles huge and significantly reducing the activity of the catalyst.

Next, zirconia with a high noble metal support rate was
．． A feature of the present invention is that it is dispersed in other multi-ω refractory inorganic oxides in the form of agglomerated particles having a relatively large average particle diameter of 5 to 20 μm. By setting the average particle diameter within this range, the interaction and reaction between the noble metal and the refractory inorganic oxide can be alleviated without impairing the efficiency of the exhaust gas purification reaction.

The zirconia used in the present invention is at least 1077
27g, preferably 60 to 100771 /U, and 2000 Å or less, preferably 500 Å
Those having the following average primary particle diameter are suitable.

Zirconia having the above-mentioned physical properties may be commercially available, or may be prepared by neutralizing an aqueous solution of zirconium salt with ammonia or the like, washing with water, drying, and firing. Furthermore, zirconia stabilized with 10% or less of an alkaline earth metal such as yttrium or calcium can also be used.

Such zirconia provides a good supporting condition when supporting the withdrawal bottom at a high supporting rate. The noble metal is supported by mixing the metal solution with zirconia, drying, firing, and reducing if necessary. At this time, the zirconia becomes agglomerated particles with a large particle size, so they are ground with a mill etc. to reduce the average particle size. The diameter is set to 0.5 to 20μ.

As the cerium oxide source used in the present invention, the starting material is not particularly limited as long as it can exist as cerium dioxide (ce02) in the catalyst. For example, commercially available C
eO2, cerium carbonate, cerium hydroxide, etc. can be used. Alternatively, a solution of a cerium salt, such as a cerium nitrate solution, may be impregnated and supported on the refractory inorganic oxide. However, by impregnating a water-insoluble cerium compound with at least lfl selected from the group consisting of a water-soluble aluminum compound and alumina hydrate, and using an alumina-modified cerium oxide obtained by firing as ceria, The catalyst according to the invention shows even better performance.

Examples of the water-insoluble cerium compound include cerium oxide, cerium hydroxide, carbonic acid, and cerium, with cerium carbonate being particularly preferred. This water-insoluble cerium compound is used in the form of fine powder, and its particle size is 0.1 to 100 microns.

In addition, examples of water-soluble aluminum compounds and/or alumina hydrates include aluminum nitrate, aluminum chloride, aluminum sulfate, gibbsite, payerite, boehmite, alumina gel, alumina sol, etc.
Particularly preferred is aluminum nitrate.

The ratio of the water-insoluble cerium compound to the water-soluble aluminum compound and/or alumina hydrate is not particularly limited, and it is possible to use effectively alumina-modified cerium oxide, but it is preferable to use an atomic ratio of cerium and aluminum. , Ce/Af! =1 to 20, particularly preferably C
e/Δ=2 to 10. Impregnating a water-insoluble cerium compound with a water-soluble aluminum compound and/or alumina hydrate is usually dried at 100 to 300°C and calcined in air at 300 to 700°C to obtain an alumina-modified cerium oxide. .

Wash-coating the thus obtained slurry containing true metal-containing zirconia and cerium oxide with adjusted particle sizes on a honeycomb carrier having an integral structure,
The catalyst is dried and, if necessary, calcined to obtain a finished catalyst.

A honeycomb carrier having an integral aJ refers to a metal monolith carrier using a ceramic carrier such as cordierite, mullite, α-alumina, or an oxidation-resistant heat-resistant metal such as stainless steel or Fe-Cr-J alloy. .

Preferred noble metal sources used in the present invention include chloroplatinic acid, dinitrodiammine platinum, palladium chloride, palladium nitrate, rhodium chloride, rhodium nitrate, and rhodium sulfate.

Examples of the refractory inorganic oxide used in the present invention include alumina, silica, titania, zirconia, magnesia, etc., and use of alumina, particularly activated alumina, is preferred. The crystal forms of alumina are γ, δ, θ, α, χ
, , and η can be used. In addition, at least one of alkaline earth elements such as calcium and barium, as well as metal elements such as chromium, manganese, iron, cobalt, nickel, and zirconium, is present in the form of an oxide.
．． Activated alumina incorporated in an amount of 1 to 30% by weight can also be used.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but it goes without saying that the present invention is not limited only to these Examples.

Example 1 A catalyst was prepared using a commercially available cordierite monolith carrier (manufactured by Nippon Insulators Co., Ltd.). The monolith carrier used had a cylindrical cross section with an outer diameter of 33 nmφ and a length of 76 mL, with a cross section of about 400 gas flow cells per square inch, and a volume of about 65 m.

A nitric acid aqueous solution of dinitrodiammine platinum is mixed with platinum (Pt) 1.5 (]) and zirconia (manufactured by Kigen Soka Kagaku Co., Ltd.) having a specific surface of 8160 TrL2/g and an average particle size of 200 7.5 (+) Mixed and dried at 120°C overnight.

Thereafter, it was fired in air at 400° C. for 2 hours to prepare a zirconia powder containing 16.7% by weight of Pt.

A rhodium nitrate aqueous solution containing rhodium (Rh) 0.3 (J) was mixed with zirconia 39 similar to the above, and 120
Dry overnight at °C. Thereafter, it was calcined in air at 400° C. for 2 hours to prepare a zirconia powder containing 9% Rh.

The above Pt-containing zirconia powder and Rh-containing zirconia powder were each placed in a mortar so that the average particle diameter of the aggregated particles was approximately 20 μm.
After grinding, the mixture was mixed with 139 g of activated alumina with a specific surface area of 100 m2/g and commercially available cerium oxide powder (Nissan Kigenso Co., Ltd. tJ) 75 (), and milled in a ball mill for 20 hours to produce an aqueous coating material. A slurry was prepared.

The monolithic carrier was immersed in this coating aqueous slurry, and after being taken out, the excess slurry in the cells was blown out with compressed air to remove all clogging. Then 130℃
After drying for 3 hours, a completed catalyst was obtained.

This catalyst coating layer is coated with Electron Pro
beMicro＾analysis (EPMA)
Photographs of the distribution of Pt and Rh were taken at 30 random locations at a magnification of 3000 times and analyzed, and it was found that P-containing zirconia and Rh-containing zirconia were each dispersed with an average particle size of 7 μm.

In addition, this catalyst has 0.065g of Pt and 0.06g of Rh0 per piece.
．． It contained 0130.

Example 2 A palladium nitrate aqueous solution containing 1.5 g of palladium (Pd) and 7.5 g of the zirconia used in Example 1 were mixed and dried at 120° C. overnight. After that, 400℃ in air
The powder was fired for 2 hours to prepare a 16.7 m % Pd-containing zirconia powder.

A finished catalyst was obtained in the same manner as in Example 1 except that the Pd-containing zirconia powder was used instead of the Pt-containing zirconia powder.

When the coating layer of this catalyst was analyzed by EPMA, it was found that the Pd-containing zirconia was dispersed with an average particle size of 5 μm, and the Rh-containing zirconia was dispersed with an average particle size of 6 μm.

This catalyst contains Pd O,065 (11Rh0.
It contained 0130.

Example 3 A chloroplatinic acid aqueous solution containing Pt0.9(+ and PdO,
A mixed solution with a palladium chloride aqueous solution containing 6a,
Mix 7.5 g of zirconia used in Example 1,
Dry overnight at °C. Thereafter, it was fired in air at 400° C. for 2 hours to produce 10fRIf 1% Pt and 5 wt% Pd-containing zirconia powder.

In Example 1, a completed catalyst was obtained in the same manner as the actual Mff4J1 except that the Pt- and PD-containing zirconia powder was used instead of the P[containing zirconia powder.

When the coating layer of this catalyst was analyzed by EPMA, the average particle size of Pt and Pd-containing zirconia was 13μ,
Rh-containing zirconia was dispersed with an average particle size of 5 μm.

This catalyst contains PL O,039g, PdO,0
It contained 26Q 1Rh O,013Q.

Actual flow example 4 Instead of zirconia used in Example 1, specific surface area 90
A finished catalyst was obtained in the same manner as in Example 1, except that zirconia (manufactured by Daiki Genso Kagaku) having an average particle diameter of 150 m/g was used.

When the coating layer of this catalyst was analyzed by EPMA, it was found that the pt-containing zirconia was dispersed with an average particle size of 0.5 μm, and the Rh-containing zirconia was dispersed with an average particle size of 1 μm.

This catalyst contained 0.065 g of Pt, RhO, 0
It contained 13a.

Example 5 A thin plate of ferritic stainless steel with a thickness of 60 μm and containing 5 m0% of aluminum and a pitch of 2.
A cylindrical gold B"A monolith carrier with an outer diameter of 33 mφ and a length of 76 mm was formed by alternately stacking and stacking corrugated sheets formed into a 5 tm corrugated shape. It had 475 gas flow cells.

Example 1 except that the gold i monolith carrier was used instead of the cordierite monolith carrier in Example 1.
A completed catalyst was obtained in a similar manner.

When the coating layer of this catalyst was analyzed by EPMA, it was found that the Pt-containing zirconia was dispersed with an average particle size of 6 μm, and the Rh-containing zirconia was dispersed with an average particle size of 7 μm.

This catalyst contains Pt O,065(+, Rh
It contained 0.013111.

Example 6 Nitrate Feb') Ram (ce (NOs)3 ・6f-1
20) 25.2g,! : Iron nitrate [Fe (No3) 3/9
Day 20] 10.1 Ill was dissolved in 100 g of pure water, mixed with 127 g of activated alumina with a specific surface Wi of 100 m 2 /g, and dried at 120° C. overnight. Then 700 in the air
IIA calcination was performed at ℃ to obtain alumina powder containing CeO2 and Fe2O3.

A completed catalyst was obtained in the same manner as in Example 1, except that the CeO2 and Fe2O3-containing alumina was used instead of 139 g of activated alumina.

When the coating layer of this catalyst was analyzed by EPMA, it was found that pt-containing zirconia and Rh-containing zirconia were each dispersed with an average particle size of 5 μm.

Moreover, this catalyst has Pt0.065o per piece.

It contained Rh0.0130.

Example 7 Aluminum nitrate CAI (NOx>3・91120)
150 rnl aqueous solution in which 65, 30 was dissolved and cerium carbonate powder (ce content 1: 47 wt 0% as CeO2) 3
19 (+), dried at 130° C. for 5 hours, and then calcined in air at 500° C. for 1 hour to produce alumina-modified cerium oxide (ce/Δ1=5 atomic ratio): JJ.

In Example 1, instead of commercially available cerium oxide powder,
A finished catalyst was obtained in the same manner as in Example 1 except for using the alumina-modified cerium oxide 75 (+) described above.

When the coating layer of this catalyst was analyzed by EPMA, it was found that P-containing zirconia and Rh-containing zirconia were each dispersed with an average particle size of 3 μm.

This catalyst contains PtO,065g, RhO,0
It contained 13o.

Real fetus example 8 Aluminum nitrate [△j! (NO3)3 ・9 H2O
) 54, 4 (220rd aqueous solution in which + was dissolved and cerium carbonate powder (ce content 1: 47% by weight as CO02)
>4260, dried at 130°C for 5 hours, and then calcined in air at 500°C for 1 hour to prepare alumina-modified cerium oxide (ce/AI=8 atomic ratio).

In Example 1, instead of commercially available cerium oxide powder,
A completed catalyst was prepared in the same manner as in Example 1, except that the alumina-modified cerium oxide 759 obtained above was used.

When the coating layer of this catalyst was analyzed by EPMA, it was found that Pt-containing zirconia and Rh-containing zirconia were both dispersed with an average particle size of 6 μm.

This catalyst contains Pt O, O'65 (1, Rh0
．． It contained 013 (l).

Example 9 94.7 g of alumina sol (containing 10% alumina by weight) and cerium carbonate (containing ce: 47% by weight as CCO2)
)340() and water 10C7 were mixed, dried at 130°C for 5 hours, and then calcined in air at 500°C for 1 hour to prepare alumina-modified cerium oxide (ce/81 to 5 atomic ratio).

The finished catalyst was prepared in the same manner as in Example 1, except that in place of the commercially available seri-cum oxide powder, alumina-modified cerium oxide 75 (l) obtained above was used.

When the coating layer of this catalyst was analyzed by EPMA, it was found that P[containing zirconia and Rh-containing zirconia were both dispersed with an average particle size of 1 μm.

This catalyst contains Pt O,065 (1, Rh0.
It contained 013111.

Comparative Example 1 An aqueous slurry for coating was prepared by milling 150 g of activated alumina with a specific surface area of 100 m 2 /Q used in Example 1 and commercially available Rerium oxide powder 750 in a ball mill for 20 hours.

This aqueous coating slurry was coated on a cordierite monolith carrier in the same manner as in Example 1. The carrier coated with activated alumina and cerium oxide was immersed in a mixed solution of a dinitrodiammine platinum nitric acid aqueous solution and a rhodium nitrate aqueous solution, pulled out, and after removing excess aqueous solution with compressed air, it was heated at 130°C for 3 hours. It was dried and calcined in air at 400° C. for 2 hours to obtain a finished catalyst.

When this catalyst coating layer was analyzed by EPMA, neither pt nor Rh particles were detected as particles larger than 0.5μ.

This catalyst has Pt O,065(+, Rh0
．． It contained 013CI.

Comparative Example 2 Specific surface area 60 m /a and average particle size 2 used in Example 1
An aqueous slurry for coating was prepared by milling 150 g of 0.00 zirconia and commercially available cerium oxide powder 75 (+) in a ball mill for 20 hours.

This aqueous coating slurry was coated on a cordierite monolith carrier in the same manner as in Example 1. PT and Rh were supported on the carrier coated with zirconia and cerium oxide in the same manner as in Comparative Example 1 to obtain a completed catalyst.

When this catalyst coating layer was analyzed by EPMA, neither Pt nor Rh particles were detected as particles larger than 0.5μ.

This catalyst contains -PtO,065(], Rh0
．． It contained 013 (l).

[Effects of the Invention] The catalyst performance of the catalysts of Examples 1 to 9 and Comparative Examples 1 to 2 after aging in an electric furnace was investigated.

The electric furnace aging was carried out in a very harsh high temperature oxidizing atmosphere by heating the catalyst in air at 900° C. for 20 hours.

The evaluation of catalyst performance after aging was conducted using a commercially available electronically controlled engine (4 cylinders 1800 cc) with a multi-converter filled with each catalyst connected to the engine exhaust system. The original performance was evaluated under the conditions of a catalyst inlet gas temperature of 450°C and a space velocity of 90°000 hr'.At this time, a 1117 sine wave type signal was introduced from an external oscillator to the engine control unit to determine the air-fuel ratio (A/F). The average air-fuel ratio was continuously changed while oscillating at ±0.5 A/F, IHz, and the catalyst inlet and outlet gas compositions at this time were analyzed simultaneously, and the average air-fuel ratio was found to be A/F = 15.1. 00% from to 14..1
The purification rates of He and NO were determined.

Plot the Co, HC, and NO purification rates vs. artificial air-fuel ratio obtained as above on a graph to create a ternary characteristic curve, and define the intersection of the Co, No purification rate curves (referred to as the crossover point). The HC purification rate corresponding to the Δ/F value at the intersection of the HC purification rate and the Δ/F value at the intersection was determined and used as the standard for evaluating the three-way performance of the catalyst.

In addition, the purification performance of the catalyst at low temperatures is determined by adjusting the air-fuel ratio by ±0.5Δ
/F, while vibrating under the conditions of IHz, the average air-fuel ratio is set to A.
/F=14. ．． 6, run the engine, install a heat exchanger in front of the catalytic converter in the engine exhaust system, and increase the catalyst inlet gas temperature from 200℃ to 500℃?
! Evaluation was made by analyzing the catalyst inlet and outlet gas compositions as they were continuously changed and determining the purification rates of coll-(c and No).

The purification rate of CO, To1c and No obtained as above is plotted against the log gas temperature containing the catalyst, and the purification rate is 5.
Determine the catalyst inlet gas temperature (T 50 ) showing 0%,
This was used as a standard to evaluate the purification performance of the catalyst at low temperatures.

Table 1 shows the results obtained by the above catalyst performance evaluation method.

Next, the catalytic activities of the catalysts of Examples 1 to 9 and the catalysts of Comparative Examples 1 to 2 after engine endurance running were investigated.

Commercially available electronically controlled engine (8 cylinders 4400CC)
A multi-converter filled with each catalyst was connected to the engine's exhaust system for durability testing. The engine was operated in a mode of steady operation for 60 seconds and deceleration for 6 seconds (fuel is cut off during deceleration and the catalyst is exposed to severe conditions of a high temperature oxidizing atmosphere), and the catalyst inlet gas temperature was 8o during steady operation. The catalyst was aged for 50 hours at 0°C.

Catalyst performance evaluation after engine endurance running was carried out in exactly the same manner as the evaluation after electric furnace aging, and three-way performance of the catalyst and purification performance at low 4 were compared. The result is the second
Shown in the table.

As is clear from Tables 1 and 2, the coating layer is made of zirconia that supports platinum, palladium, and rhodium disclosed in the present invention at a high loading rate as agglomerated particles having an average particle diameter in the range of 0.5 to 20μ. The catalysts of Examples 1 to 9, which were dispersed in the catalyst, all exhibited significantly superior catalytic performance than the catalysts of Comparative Examples 1 and 2, in which the metal was supported in a conventional manner.

Moreover, the catalysts of Examples 7 to 9, which used alumina-modified cerium oxide as the cerium oxide, exhibited even higher performance.

From the above summary, it is clear that the catalyst disclosed in the present invention has excellent durability with little deterioration even under severe conditions such as high temperature oxidizing atmosphere as well as under normal engine running conditions.

Patent applicant Nippon Shokubai Chemical Co., Ltd. Procedure supplement
Authorized letter (spontaneous) Date: C, 1986 Mr. Akio Kuroda, Commissioner of the Japan Patent Office 11
, Indication of the case 1986 Patent Application No. 1'73 S1 No. 2, Name of the invention Exhaust gas purification catalyst 3, Relationship with each case to be amended Patent applicant Korai, Higashi-ku, Osaka City, Osaka Prefecture! n 5th Street 1〉.

・'9 4. Hair to be corrected (1) In the specification, page 11, line 10, [...
・Alkaline earth elements, chromium in L...
is corrected to "...alkaline earth elements, rare earth elements such as lanthanum and cerium, and chromium...".

2) On page 20, line 7 of the same page, change "...Alumina obtained from the above..." to "...Alumina obtained from the above..."・
” is corrected.

Claims (1)

[Claims] (1) 5 to 30% by weight of platinum and/or palladium
Zirconia (a) supported with zirconia (a) and/or zirconia (b) supported with 1 to 20% by weight of rhodium, respectively,
Exhaust gas purification characterized by comprising a catalyst composition containing cerium oxide (c) in the form of agglomerated particles with an average particle diameter of 20 μm, which is coated and supported on a honeycomb carrier having an integral structure. Catalyst for use. (2) The catalyst composition contains the zirconia (a) and/or
or (b), the catalyst according to claim (1), comprising the cerium oxide (c) and further a refractory inorganic oxide (d). (3) 1 to 20 g of the zirconia (a) and/or (b) and the cerium oxide (
The catalyst according to claim (2), wherein c) is supported in an amount of 1 to 150 g as CeO_2 and further 50 to 200 g of the refractory inorganic oxide (d). (4) The zirconia used is at least 10 m^2/
g, and the average particle size of its primary particles is 2.
000 Å or less, or (1), (2) or (
3) Catalyst as described. (5) The catalyst according to claim (2), (3) or (4), wherein the refractory inorganic oxide (d) used is activated alumina. (6) The cerium oxide (c) is alumina-modified cerium obtained by impregnating a water-insoluble cerium compound with at least one selected from the group consisting of a water-soluble aluminum compound and an alumina hydrate and firing the impregnated water-insoluble cerium compound. The catalyst according to claim (1), (2), (3), (4) or (5), which is an oxide. (7) The water-insoluble cerium compound is cerium carbonate,
A patent claim characterized in that the water-soluble aluminum compound is selected from the group consisting of cerium oxide and cerium hydroxide, and the water-soluble aluminum compound is selected from the group consisting of aluminum nitrate, aluminum chloride, and aluminum sulfate. The catalyst according to range (6). (8) The catalyst according to claim (6) or (7), wherein the alumina-modified cerium oxide has a composition in which the atomic ratio Ce/Al of cerium to aluminum is 1 to 20.