JPS62266142A - Catalyst for treating exhaust gas - Google Patents

Abstract

PURPOSE:To enhance the purifying capacity of exhaust gas, by supporting a catalytic metal such as platinum by a mixture of activated alumina supporting a rare earth metal and rare earth metal oxide to prepare a slurry and applying said slurry to a support. CONSTITUTION:One or more kind of a catalytic metal selected from a group consisting of platinum, rhodium and palladium by a powder mixture of activated alumina supporting a rare earth metal and rare earth metal oxide and an alumina sol containing a reductive solution is subsequently added to the resulting powder to prepare a slurry. After this slurry is applied to a catalyst carrier, the coated one is dried and baked to obtain an exhaust gas treatment catalyst removing hydrocarbon, carbon monoxide and nitrogen oxide in the exhaust gas of an internal combustion engine. The total amount of the noble metals being catalytic metals is pref. about 0.05-0.35wt%.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is directed to the treatment of hydrocarbons (01C), carbon monoxide (Co), and nitrogen oxides (01C), carbon monoxide (Co), and nitrogen oxides (
This invention relates to an exhaust gas treatment catalyst for simultaneously removing NO, ).

(Prior art) As a conventional exhaust gas treatment catalyst, for example, U.S. Pat.
, 565,830, catalyst metals such as platinum and rhodium are supported on a support obtained by coating a cordierite monolithic support with activated alumina using an impregnation method. There have been proposed catalysts obtained by using an impregnation method to support platinum, rhodium, etc. on a carrier obtained by coating activated alumina containing cerium in advance.

(Problems to be Solved by the Invention) However, in such conventional exhaust gas treatment catalysts, platinum, rhodium, etc. are dispersed and supported on the surface of activated alumina coated on an integrated carrier. Because there is
Thermal deterioration of alumina itself promotes sintering of platinum, rhodium, etc., resulting in a decrease in catalyst active sites, making it impossible to maintain durability, and impregnating platinum, rhodium, etc. Because this method uses a method, the distribution of platinum, rhodium, etc. does not become uniform in response to changes in the alumina layer, so there was a problem that sufficient catalytic activity, especially initial activity, could not be brought out. .

(Means for Solving the Problems) This invention was made by focusing on such conventional problems, and uses rare earth metal nitrates to form T- or δ-alumina that has previously supported rare earth metals. One or more noble metals selected from the group consisting of platinum, rhodium, and palladium are dispersed and supported on the powder obtained by mixing activated alumina and rare earth oxide powder, which are the main components, and then a reducing solution is added. The above-mentioned problems have been solved by a catalyst obtained by coating an integrated carrier with a slurry obtained by mixing and pulverizing the powdered catalyst obtained by the process and an alumina sol containing a reducing solution, and then drying and calcining the slurry.

Therefore, this invention provides a reduction property after supporting one or more catalytic metals selected from the group consisting of platinum, rhodium, and palladium on a powder mixture containing activated alumina supported on a rare earth metal and a rare earth metal oxide. Hydrocarbons in the exhaust gas of an internal combustion engine, which is obtained by coating a catalyst carrier with a slurry obtained by adding an alumina sol containing a reducing solution to a powder obtained by adding a solution, followed by drying and firing. , relates to an exhaust gas treatment catalyst that removes carbon monoxide and nitrogen oxides.

The catalyst of the present invention contains a rare earth metal in advance, which is obtained by impregnating and supporting an inorganic carrier mainly composed of activated alumina with a rare earth metal nitrate in an amount such that the ratio of the rare earth metal to the alumina is 1 to 5% by weight. Activated alumina support and rare earth oxide are added as rare earth metal to total solid content of 5
One or more, preferably two or more or three noble metals selected from the group consisting of platinum, rhodium and palladium are added to the powder obtained by mixing the powder to a weight of ~50% by weight.
It can be obtained by supporting it on a powder carrier by any production method, but it is particularly preferable to add an aqueous nitric acid or hydrochloric acid solution to the nitric acid or hydrochloric acid solution of the noble metal in an amount such that the hydrogen ion concentration (Pl+) is 1.0 or less. After impregnating the nitrate or hydrochloride of a noble metal by an impregnation method using a solution, a reducing solution such as acetic acid or formic acid is added, and after drying, the temperature is preferably 350°C or higher and 600°C or lower in an air stream. A powdered catalyst is made by calcination at a temperature of 2 hours. In this powder catalyst preparation method, the above-mentioned impregnation method is used in advance to prepare the rare earth metal-containing activated alumina and rare earth oxide mixed powder in the form of a nitrate or hydrochloride of the noble metal and in the presence of free nitric acid or hydrochloric acid, the pH is set to 1.0 or less. This allows a particularly high degree of dispersion on activated alumina, which provides catalytic active sites on the support, and then the addition of acetic acid or formic acid to accelerate the metalation of the precious metal on the alumina at low temperatures. . At this time, acetic acid is CH+C00II ' 2C1lOII (decomposition) 2CHOH+ 20□-su2CO2+21120
It is thought that a two-step reaction (heat sintering) occurs. The same applies to formic acid. In this reaction, aldehyde (formaldehyde in this case), which is a decomposition product, removes oxygen and burns, so it acts as a reducing agent, prevents noble metal salt decomposition products from becoming oxides, and promotes metallization. Conceivable. This fact can be seen in the thermal analysis of samples to which acetic acid was added (
(in the air) can also be estimated from the results. Thereafter, after drying as described above, the acetic acid or formic acid added is decomposed by drying at 350°C to 600°C in an air stream, and the resulting aldehyde promotes the decomposition and metalization of the noble metal salt. Precious metal particles are supported in a highly dispersed manner in the powdered catalyst. The powdered catalyst thus obtained and the alumina sol containing the reducing solution such as acetic acid or formic acid are pulverized and kneaded using a pot mill or the like to obtain a slurry.

The purpose of adding rare earth metals to an inorganic support mainly composed of activated alumina is that the added rare earth metal nitrates are decomposed into rare earth metal oxides with excellent heat resistance by calcination, but at this time, the solid solution with alumina is making and improving the heat resistance of alumina. The amount of the rare earth metal nitrate added is such that the rare earth metal oxide obtained by firing is 1 to 5% by weight of the alumina as a metal.
If it is less than 1% by weight, the effect will be small, and if it exceeds 5% by weight, the heat resistance will improve, but the specific surface area of alumina will be relatively reduced.

The rare earth oxide that is mixed next adsorbs oxygen when the atmosphere in which the catalyst of the present invention is used changes, that is, when there is an excess of oxygen, and desorbs oxygen when there is a lack of oxygen.
) It is added to obtain a storage effect and a promoter effect at the same time, and the amount of rare earth metal added as a rare earth metal oxide is 5 to 50% by weight as a metal based on the total solid content in the slurry. If it is less than 5% by weight, no sufficient effect can be expected, while if it exceeds 50% by weight, the specific surface area will decrease due to a relative decrease in the amount of alumina in the coating layer, which is not preferable.

Next, the slurry obtained as described above is coated on a coated integral carrier mainly composed of silica, alumina, and magnesia, dried, and then calcined in a combustion gas atmosphere to form a catalyst. The firing temperature at this time is 350℃~6
It is desirable to set the temperature to 00°C, maintain this temperature range for 0.5 to 2 hours, and perform firing in a temperature rising and slow cooling pattern. The amount of noble metal supported in the catalyst of this invention is such that the total amount of one or more noble metals among platinum, rhodium, and palladium is 0.05 to
When rhodium is included at 0.35% by weight, the ratio of rhodium to other noble metals is preferably in the range of 1:1 to 20:1. This is because if the noble metal amount is less than 0.05% by weight, the purification rate will decrease, and if it exceeds 0.35% by weight, little improvement in the purification rate is expected. Regarding the ratio of metals,
This is because when the rhodium content exceeds other noble metals, the hydrocarbon purification rate decreases, and when it becomes less than 1720, the NoX purification rate decreases.

The catalyst of the present invention is characterized by having the structure described above, and has significantly improved low-temperature activity and durability, so it has a small amount of precious metals supported, high efficiency, and is suitable for internal combustion. This system makes it possible to simultaneously remove IIc, Co, and NOX, which are harmful components in exhaust gas from engines, especially automobiles. This means that conventional catalysts for the simultaneous removal of the three harmful components listed above are required to have a high level of processing performance, especially excellent durability, while on the other hand, precious metals such as platinum and rhodium used for exhaust gas treatment are expensive. Naturally, there are restrictions on the amount used, and the amount of precious metals is low.
This is an epoch-making development in the current climate of developing high-performance catalysts.

(Example) The present invention will be explained in detail using the following Examples, Comparative Examples, and Test Examples.

The specific surface area according to the B, E, and T methods on large ships is 200 m"/g,
Activated alumina powder 1000 whose main component is gamma or delta alumina with a maximum pore frequency diameter of 100 Å or less
96.34g of cerium nitrate to 11g of ion-exchanged water
000 g of the solution was added, stirred well, dried at 150°C for about 3 hours in an open air stream, and dried in an air stream for 6 hours.
After firing at 00° C. for 2 hours, a cerium-containing activated alumina powder was obtained. 443.34 g of cerium oxide was dry-pulverized and mixed with 1000 g of this activated alumina powder to obtain an alumina-ceria mixed powder. This mixed powder 3000
g, dinitrodiammine platinum nitric acid solution containing 18.5 g of platinum, and nitric acid containing 1.85 g of rhodium.
Mix the dium solution and add ion-exchanged water to 1800 m
After A, the hydrogen ion concentration (
Pl+) was added until it became 1.0 or less, and to the obtained solution,
Added with stirring. After 60 minutes, 10% by weight acetic acid solution 1
80+nj! was added, stirred for another 10 minutes, the entire amount was transferred to a drying container, and dried using a microwave dryer. Next, the mixture was calcined in an air stream at 400° C. for 2 hours to obtain platinum/rhodium supported catalyst powder. This catalyst contains 0.616% by weight of platinum and 0.0616% by weight of rhodium in terms of metals.
It contained.

1608 g of the powdered catalyst obtained above and acetic acid acidic alumina sol (10% by weight suspension of boehmite alumina) were added.
A porcelain bot mill was filled with 2,392 g of the sol obtained by adding % by weight of CH3CO0H, and pulverized and mixed to obtain a slurry liquid. Using this slurry liquid, a cordierite monolithic support (1, i, 400 cell) containing alumina, silica, and magnesia as main components was coated, dried, and fired to obtain catalyst 1. The amount of coating at this time was set at 340 g/piece. The resulting catalyst 1 contained 111.5 g of ceria and 1.91 g of platinum and 0.191 g of rhodium per monolithic support.

Implementation ■1 In Example 1, 3000 g of mixed powder of cerium-containing activated alumina and ceria were mixed with a dinitrodiammine platinum nitrate solution containing 7.46 g of platinum and a rhodium nitrate solution containing 1.24 g of rhodium. After adding ion-exchanged water to make the volume 1800 m 12 , a 10% by weight nitric acid solution was added until the hydrogen ion concentration (PH) became 1.0 or less, and the mixture was added to the resulting solution with stirring.

After 60 minutes, 180 ml of a 10% by weight acetic acid solution was added, and the same procedure was repeated to obtain catalyst 2. This catalyst 2 contained 11.5 g of ceria and 0.772 g of platinum per integral carrier;
It contained 0.129g of rhodium.

Cerium-containing activated alumina powder 100 in Example 1
3000 g of alumina and ceria mixed powder obtained by dry mixing 296.33 g of cerium oxide per 0 g of dinitrodiammine platinum nitric acid solution containing 18.5 g of platinum and a rhodium nitrate solution containing 1.85 g of rhodium. Mix and add ion exchange water to 1800n+j! After 1 hour, the 10 wt% nitric acid solution was adjusted to hydrogen ion concentration (PI()
It was added to the resulting solution while stirring. After 60 minutes, 180 m j of 10 wt% acetic acid solution
+ was added, and Catalyst 3 was obtained in the same manner. This catalyst 3 contained 78.1 g of ceria per integral carrier and 1.0 g of platinum.
It contained 91 g and 0.191 g of rhodium.

Example 4 In Example 3, 3000 g of mixed powder of cerium-containing activated alumina and ceria was mixed with a dinitrodiammine platinum nitric acid solution containing 7.46 g of platinum and a rhodium nitrate solution containing 1.24 g of rhodium, and ions were prepared. After adding exchanged water to bring the volume to 1800ml, a 10% by weight nitric acid solution was added until the hydrogen ion concentration (PH) became 1.0 or less, and the mixture was added to the resulting solution with stirring.

After 60 minutes, add 1BOn+ 10% acetic acid solution,
Catalyst 4 was obtained in the same manner. This catalyst 4 contained 78.1 g of ceria and 0.772 g of platinum per integral carrier.
, contained 0.129 g of rhodium.

3000 g of alumina/ceria/lantana mixed powder obtained by dry mixing 329.2 g of cerium oxide and 110.8 g of lanthanum oxide per 1000 g of platinum.
A dinitrodiammine platinum nitric acid solution containing 8.5 g and a rhodium nitrate solution containing 1.85 g of rhodium were mixed, ion-exchanged water was added to make a total volume of 1800 ml, and the 10% by weight nitric acid solution was mixed with a hydrogen ion concentration (PH) of 1. .0 or less, and added to the resulting solution with stirring. After 60 minutes, 18011IIl of a 10% by weight acetic acid solution was added, and catalyst 5 was obtained in the same manner. This catalyst 5 is formed on an integral carrier 1
Each piece contained 78.1 g of ceria, 23.9 g of lantana, 1.91 g of platinum, and 0.191 g of rhodium.

In Example 5, 3000 g of mixed powder of cerium-containing activated alumina, ceria, and lantana was mixed with platinum, tare, 4
Mixing a dinitrodiammine platinum nitrate solution containing 6 g and a rhodium nitrate solution containing 1.24 g as rhodium,
After adding ion exchange water to make it 1800+m It, 1
A 0% by weight nitric acid solution was added until the hydrogen ion concentration (PH) was 1.0, and added to the resulting solution with stirring. After 60 minutes, 180mj+ of a 10% by weight acetic acid solution was added, and catalyst 6 was obtained in the same manner. This catalyst 6 contained 78.1 g of ceria and 23.9 g of lantana, 0.772 g of platinum, and 0.129 g of rhodium per monolithic support.

In Example 5, 3000 g of cerium-containing activated alumina, ceria, and lantana mixed powder were mixed with a dinitrodiammine palladium nitric acid solution containing 18.5 g of palladium and a rhodium nitrate solution containing 1.85 g of rhodium. After adding ion exchange water to make 1800ml,
A 10% by weight nitric acid solution was added until the hydrogen ion concentration (pH) was 1.0, and added to the resulting solution while stirring. 60
After a few minutes, a 10% by weight acetic acid solution 1B (In 1) was added, and the same procedure was repeated to obtain a catalyst 7.
Each piece contained 78.1 g of ceria, 23.9 g of lantana, 1.91 g of palladium, and 0.191 g of rhodium.

In Example 5, 3000 g of cerium-containing activated alumina, ceria, and lantana mixed powder was mixed with 9.2 g of platinum.
A dinitrodiammine platinum nitrate solution containing 24 g, a dinitrodiammine palladium nitrate solution containing 9.224 g as palladium, and a rhodium nitrate solution containing 1.85 g of rhodium were mixed, and ion-exchanged water was added to give a solution of 1,800 g.
mg, and then added a 10% by weight nitric acid solution until the hydrogen ion concentration (PH) reached 1.0, and added to the obtained solution while stirring. After 60 minutes, 180ml of 10% by weight acetic acid solution
1 was added thereto, and Catalyst 8 was obtained in the same manner. This catalyst 8 contained 78.1 g of ceria and 23.1 g of ceria per monolithic support.
9g of lantana, 0.955g of platinum, 0.9g of palladium
55 g, containing 0.191 g of rhodium.

Example 9 In Example 1, 3000 g of mixed powder of cerium-containing activated alumina and ceria was mixed with a chloroplatinic acid solution containing 18.5 g of platinum and a rhodium chloride solution containing 1.85 g of rhodium, and ions were prepared. Add replacement water 18
After the solution was adjusted to 00 mIl, a 10% by weight hydrochloric acid solution was added until the hydrogen ion concentration (PH) became 1.0 or less, and the mixture was added to the obtained solution while stirring. After 60 minutes, 180 mA of a 10% by weight acetic acid solution was added, and the mixture was further stirred for 10 minutes, and the entire amount was transferred to a drying container and dried using a microwave dryer. The platinum was then fired at 600°C for 2 hours in a stream of air.
Catalyst 9 was obtained in the same manner except that rhodium-supported catalyst powder was obtained. This catalyst 9 weighs 111.5 g per monolithic carrier.
ceria and 1.91 g of platinum.

It contained 0.191 g of rhodium.

Activated alumina granular carrier 1437. Og and alumina sol (
10% by weight H in a 10% by weight suspension of boehmite alumina
Sol obtained by adding NO3>2563
．． After filling 0 g into a pot mill and pulverizing for 6 hours, the resulting slurry was adhered to an integrated carrier (1,71,400 cells) mainly composed of cordierite, and calcined at 650° C. for 2 hours. The amount of adhesion at this time was set at 340 g/piece.

Next, this alumina-adhered carrier was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride to support the platinum and rhodium in amounts of 1.91 g of platinum and 0.191 g of rhodium, and then heated at 600°C. After firing for 2 hours, catalyst A was obtained.

Activated alumina granular carrier 1437. supports 5% by weight of cerium in terms of cerium metal. Og and alumina sol 25
Catalyst B was obtained in the same manner as in Comparative Example 1 except that 63.0 g was used. However, the amount of platinum and rhodium deposited is 1.91 g of platinum and 0.191 g of rhodium per integrated carrier.
It was set to

454.3 g of activated alumina granular carrier supporting 50% by weight of cerium in terms of cerium metal and alumina sol 2
Catalyst C was prepared in the same manner as in Comparative Example 1 except that 563 g was used.
I got it. However, the amount of deposited platinum and rhodium was set to 1.91 g of platinum and 0.191 g of rhodium per one integrated carrier.

Chloroplatinic acid, rhodium chloride, and cerium oxide are added to an alumina slurry containing pialite alumina and amorphous alumina hydroxide, treated with hydrogen sulfide (Has), dried, and calcined at 340°C. US Patent No. 3,56
A catalyst (according to the method of Example Kari in the specification of No. 5,830) was obtained. This catalyst contains 1.12 g/IL of platinum, 0.112
It contained 41 g/41 rhodium, 14.4 g/1 ceria and 31 g/1 alumina.

The catalysts 1 to 9 obtained in Examples 1 to 9 and the catalysts A to D obtained in Comparative Examples 1 to 4 were subjected to actual vehicle durability (engine durability) under the following conditions, and the purification rate of 10 mode emission was determined. was measured and shown in Table 1 as the purification rate m.

King-no-sho l Salmon Kujoka catalyst Integrated precious metal catalyst Catalyst outlet temperature 750℃ Space velocity Approximately 70,000 Hr-' Durability time 100 hours Engine displacement 2200cc oz 0.5±0.1% NO1001000 pp 2500ppm COz 14.9±0.1% Table 1 (Effects of the invention) As explained above, the catalyst of the present invention is made of active alumina containing rare earth metal and rare earth metal. After supporting a catalyst metal on a mixed powder of oxide powder, the catalyst powder obtained by adding a reducing solution and an alumina sol containing a reducing solution are mixed and pulverized, and a slurry obtained is coated on an integrated carrier, Since it is obtained by drying and firing, Pt, R
It is possible to prevent a decrease in the number of active sites, including a decrease in the surface area of the noble metal due to sintering such as h, and the purification rate is significantly improved and the durability is improved compared to the conventional integrated noble metal catalyst. Furthermore, this provides the effect of showing equivalent or higher efficiency than conventional catalysts even with a low amount of noble metal.

Claims (1)

[Claims] 1. After supporting one or more catalyst metals selected from the group consisting of platinum, rhodium, and palladium on a powder mixture containing activated alumina supporting a rare earth metal and a rare earth metal oxide, a reducing solution is applied. Hydrocarbons in the exhaust gas of an internal combustion engine, characterized by coating a catalyst carrier with a slurry obtained by adding an alumina sol containing a reducing solution to the powder obtained by adding the alumina sol, followed by drying and firing.
Exhaust gas treatment catalyst that removes carbon monoxide and nitrogen oxides.