JP2930975B2 - Method for producing combustion catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to purification of exhaust gas containing harmful components such as carbon monoxide and hydrocarbons discharged from automobiles and various factories, and purification of methane (CH ₄ ), The present invention relates to a catalyst used for combustion of a flame-retardant fuel such as propane (C ₃ H ₈ ), and more particularly to a catalyst having excellent heat resistance and low-temperature activity and a method for producing the same.

[Conventional technology]

The catalytic combustion method purifies carbon monoxide and hydrocarbons in automobile exhaust gas, purifies harmful components such as ethyl acetate and aldehyde in exhaust gas from various factories, or purifies methane (CH ₄ ) and propane gas (C ₃ H _8). ) Is widely used for flameless combustion of flame-retardant fuels. The catalyst system used at this time is mainly an alumina-based catalyst which carries a noble metal such as platinum (Pt) or palladium (Pd). However, since the heat resistance of the catalyst is insufficient, its operating temperature is low. Need to be limited or controlled. For example, a so-called three-way catalyst in which platinum is the main component and rhodium is supported on an alumina carrier in an amount of about 1/5 to 1/20 is widely used as a catalyst for automobile exhaust gas purification. However, such a catalyst rapidly deteriorates when used in a condition exceeding 600 ° C. in an oxidizing atmosphere. This is because excess oxygen in the gas phase combines with platinum (Pt), which forms an active site in the catalyst, to form platinum oxide (PtO ₂ ), which further sinters into giant particles and turns into a catalytic active site. (Japanese Patent Publication No. 63-24418, Wakamiya, Nakamura, Catalyst, 21 , 98
−103 (1979)). Also, in a high temperature range where the carrier side causes sintering, the so-called Earthquake Effect, which is induced by the sintering and promotes the sintering of the catalyst component to cause significant deterioration of the catalyst, is also considered to be one of the causes of thermal deterioration of the catalyst. (Matsuda, Yamashita, Catalyst, 29 , 293-298 (198
7)). Against this background, studies to improve the heat resistance of the catalyst have been made from both sides of the catalyst component and the carrier, and there is a method of improving the heat resistance of the catalyst by adding an alkaline earth compound or a rare earth element compound. Many proposals have been made (JP-A-61-28453, JP-A-61-245844, JP-A-61-245844).
No. 2-1454, Proceedings of the 56th Symposium on Catalysis (A), 4N1
7, 192 (1985), JP-A-61-38627, JP-B-63-24418
No. JP-A-61-84636). The intent of these methods is
Add an alkaline earth element or rare earth compound,
It is said to stabilize alumina as a carrier and to suppress a decrease in the oxygen activating ability of the active ingredient. For automotive exhaust gas purification catalysts, ceria (CeO ₂ ) is added to expand the catalyst window width (air-fuel ratio region where the simultaneous removal rate of carbon monoxide, hydrocarbons and nitrogen oxides is high) and to improve heat resistance. This is thought to be due to the oxygen storage capacity based on the following formula of ceria (Taguchi, Catalysis, 29 , 605-609 (1987)).

2CeO ₂ → Ce ₂ O ₃ + 1 / 2O ₂ (1) The present inventors have developed a combustion catalyst which is less deteriorated even in a temperature range of 700 to 1,000 ° C. in an oxidizing atmosphere, has high activity, and can be used for a long time. In the process of proceeding, as a result of detailed examination of the effect of adding the alkaline earth element or rare earth compound,
Lanthanum (La) is one of the elements having a particularly high effect, and it has been found that there is a remarkable difference in the expression of the effect depending on the method of adding the lanthanum compound. When the catalyst is used under a temperature condition of 1,000 ° C. or less, the heat resistance of the catalyst component is more important than the heat resistance of the carrier. The purpose of the conventional addition of the lanthanum compound is was to increase the thermal stability of the alumina support, to produce a lanthanum aluminate (LaAlO ₃₎ comprising a compound having a perovskite structure, there selectively precious metal component It became clear that the heat resistance of the catalyst component was increased when supported.

[Problems to be solved by the invention]

Hitherto, lanthanum aluminate has been considered to be undesirable when present in a catalyst because of its small surface area (for example, JP-A-62-180751). No. 282640), which is expected to have an oxygen storage property derived from the perovskite structure, and is not directly aimed at improving the heat resistance of the catalyst component itself. In the catalyst of the present invention, the active component is not always supported on the lanthanum aluminate, and the effect of the alkaline earth or rare earth element compound cannot be sufficiently exerted. Therefore, the utilization of the expensive noble metal component in the catalyst is insufficient. Was.

The present invention improves the inadequate points of the above-mentioned conventional invention, effectively extracts the effect of adding a lanthanum compound on the improvement of the heat resistance of the supported noble metal catalyst, obtains a high-performance catalyst, and sufficiently reduces the noble metal as an active component. It is intended to be used for

[Means for solving the problem]

The above object is achieved by obtaining a supported noble metal catalyst by supporting a noble metal component on lanthanum aluminate, and then adding the noble metal component to a refractory inorganic carrier to cover the surface area thereof.

That is, the present invention uses a refractory inorganic carrier as a first component,
Lanthanum aluminate as the second component, a method for producing a combustion catalyst having at least one noble metal selected from platinum and palladium as the third component, wherein the noble metal component is supported on a previously prepared lanthanum aluminate, It is characterized by being coated on the surface of the refractory inorganic carrier as the first component.

In the present invention, lanthanum aluminate is preferably prepared by reacting α-alumina with a lanthanum compound.

[Action]

In the conventional invention, an alumina carrier having excellent thermal stability is obtained by adding a lanthanum compound to a transition surface alumina having a high surface area such as γ, θ, and δ, followed by firing, and then supporting a catalyst component. In this method, since various reaction products of lanthanum and alumina are dispersed and generated in the carrier, as shown in FIG. 1, the noble metal as a catalyst component is deposited on the alumina or alumina-lanthanum reaction product. Is non-selectively supported. In other words, in the conventional catalyst, the noble metal supported on lanthanum aluminate has high activity and high heat resistance, but the other noble metals have not improved heat resistance. Could not be used for a period.

The present invention focuses on the fact that a compound called lanthanum aluminate is a substance that increases the heat resistance and activity of a supported noble metal catalyst, and by selectively supporting a noble metal component on the compound, the performance of the catalyst is improved. To bring out the best. The noble metal component supported on lanthanum aluminate causes an electronic interaction with La. That is, it is considered that the transfer of electrons from La to the noble metal component causes the noble metal to exhibit a reduced state, and this is stably maintained.

In the catalyst according to the present invention, as shown in FIG. 2, the lanthanum aluminate supporting the noble metal is dispersed on the refractory inorganic carrier and covers the surface thereof, so that the catalyst has high activity and high heat resistance. Can be realized. Particularly, the method using α-alumina when obtaining the lanthanum aluminate is excellent as an economical and easy method. Since α-alumina is stable and has an extremely small surface area of 10 m ² / g or less, when reacting with a lanthanum compound, the quantitative relationship between La and Al is favorable for obtaining lanthanum aluminate (La: Al = 1: It is thought to be 1). In other words, when a high surface area and active alumina raw material is used, the amount of Al around La becomes larger than the equivalent amount, and the probability that by-products such as lanthanum β-alumina (La ₂ O ₃ · 11Al ₂ O ₃ ) are formed Will be higher. In contrast, when α-alumina with a small surface area is used as the alumina raw material,
The amount of Al becomes close to the equivalent amount, and lanthanum aluminate is easily produced selectively. Further, as an advantage of using α-alumina, even if unreacted α-alumina remains,
It may be negligible because of its extremely small surface area. That is, the amount of the noble metal supported on α-alumina, which is inert and has a small surface area, is almost negligible, and wasteful noble metal components can be suppressed as much as possible. It is a feature of the present invention that the characteristics of α-alumina, which is conventionally inactive and unfavorable as a raw material for the catalyst carrier, are used in reverse.

〔Example〕

As the refractory inorganic carrier used in the present invention, alumina, cordierite and the like can be used,
A carrier having a surface area and a pore volume as large as possible is preferable, and the specific surface area is desirably 60 m ² / g and the pore volume is 0.1 ml / g or more.

To obtain lanthanum aluminate, an aluminum compound is reacted with a lanthanum compound. As the aluminum compound at this time, transition alumina such as γ, θ, and δ, aluminum nitrate, and the like can be used, and the method using α-alumina is preferable for the above-mentioned reason. As the α-alumina, those having as high a purity as possible and having a fine particle diameter are preferable, and those having a purity of 90% or more and a particle diameter of 3 μm or less are desirable. Use of a coprecipitation method or an alkoxide method is preferable because lanthanum aluminate having high uniformity and a small particle diameter can be obtained. Lanthanum raw materials include lanthanum nitrate (La (NO ₃ ) ₃ ) and lanthanum acetate (La (C
H ₃ COO) ₃ ) can be used.

In order to obtain lanthanum aluminate, an alumina raw material and a lanthanum compound are mixed, and then heated and fired to cause a reaction. At this time, the firing temperature is preferably 1,100 ° C. or less. Above this, the crystal growth of lanthanum aluminate is remarkable, the surface area of the catalyst becomes small, and the noble metal component cannot be sufficiently dispersed.

After supporting the catalyst component, the catalyst can be used as a catalyst by a usual preparation method. However, in order to firmly fix the noble metal component on the lanthanum aluminate, it is preferable to perform calcination at a temperature of 400 to 800 ° C.

The wet kneading method is effective for dispersing and supporting lanthanum aluminate alone or a lanthanum aluminate carrying a noble metal component on the refractory inorganic carrier. At this time, the lanthanum aluminate particles are preferably as fine as possible, and the average particle diameter is desirably 1 μm or less.

When the catalyst is actually used, the shape of the refractory inorganic carrier can be selected from granules, columns, rings, plates, fibers, honeycombs, and other shapes suitable for use conditions. A refractory inorganic carrier such as alumina having a higher specific surface area may be coated on the refractory inorganic carrier in advance, and lanthanum aluminate may be coated thereon.

Next, the present invention will be described in detail using specific examples.

Reference Example 1 40 g of aluminum nitrate and 60.9 g of lanthanum nitrate were distilled water.
Dissolved in 500 ml and added 28% aqueous ammonia with vigorous stirring to form a precipitate. It was heated and evaporated to dryness, which was then dried in air at 120 ° C. for 24 hours. The obtained powder was calcined in the atmosphere at 1,000 ° C. for 2 hours to obtain lanthanum aluminate. This is a ball mill 24
After wet pulverization for 0.5 hour to average particle size, distilled water 500
well dispersed in ml. The average particle size is 3 μm, specific surface area
After adding 110 g of 160 m ² / g of γ-alumina and stirring for 1 hour, the lanthanum aluminate was supported on the γ-alumina surface by heating to evaporate water. This powder was fired at 600 ° C. in the air for 5 hours to form a lanthanum aluminate coating layer on the γ-alumina surface. This powder is wet-ground with a ball mill for 24 hours to an average particle size of 0.5 μm,
Further, the water content was appropriately adjusted and stirred to obtain a 50% slurry. To this slurry was added 100 ml of an aqueous solution of tetraammineplatinum (II) nitrate (Pt (NH ₃ ) ₄ (NO ₃ ) ₂ ) prepared so that the amount of supported platinum on the catalyst was 1.0 wt%, followed by stirring for 1 hour. Then, the mixture was heated and kneaded and evaporated to dryness. The obtained powder was dried in air at 120 ° C. for 4 hours, calcined at 550 ° C. for 2 hours, and pulverized appropriately to obtain a granular supported platinum catalyst of 10 to 20 mesh (platinum supported amount: 1 wt%).

Reference Example 2 In Reference Example 1, 40 g of aluminum nitrate was replaced with α-alumina (Sumitomo Aluminum Refining Co., Ltd.'s easily sinterable alumina AE).
S-11) A granular catalyst was obtained in the same manner except that lanthanum aluminate was obtained by a kneading method instead of a coprecipitation method by setting it to 20 g.

Example 1 40 g of aluminum nitrate and 60.9 g of lanthanum nitrate were distilled water
Dissolved in 500 ml and added 28% aqueous ammonia with vigorous stirring to form a precipitate. After it was heated and evaporated to dryness, it was dried in air at 120 ° C. for 24 hours. The obtained powder was calcined in the atmosphere at 1,000 ° C. for 2 hours to obtain lanthanum aluminate. This was wet-pulverized with a ball mill for 24 hours to obtain an average particle diameter of 0.8 μm, and water was appropriately added and stirred to obtain a 50% slurry. 100 ml of an aqueous solution containing 2.59 g of tetraammineplatinum (II) nitrate
After stirring for about 1 hour, calcination is performed at 550 ° C. for 2 hours in the atmosphere, and platinum is supported on lanthanum aluminate.
Fixed. This powder was wet-pulverized with a ball mill for 24 hours to an average particle size of 0.5 μm or less, and then added to 500 ml of distilled water and dispersed well. The average particle size is 3 μm and the specific surface area is
After adding 110 g of 160 m ² / g of γ-alumina and stirring for 1 hour, the mixture was heated, evaporated to dryness, and dried in air at 120 ° C. for 24 hours. Next, calcination was performed at 550 ° C. for 2 hours in the atmosphere, and lanthanum aluminate supporting platinum was supported and fixed on the γ-alumina. This was appropriately pulverized to obtain a granular catalyst of 10 to 20 mesh.

Reference Example 3 In Reference Example 1, 100 ml of an aqueous solution of tetraammineplatinum (II) nitrate was replaced with 100 ml of an aqueous solution of palladium nitrate (palladium content: 4.0 g), and the calcination temperature of the catalyst was changed from 550 ° C. to 700
A catalyst was used in the same manner except that the temperature was changed to ° C (palladium loading 3 wt%).

Example 2 Example 1 was repeated except that tetraammineplatinum (II) nitrate was used.
Replace 100 ml of the aqueous solution containing 2.59 g with an aqueous palladium nitrate solution containing 4.0 g of palladium, and carry the noble metal component on lanthanum aluminate, and set the firing temperature to 70 when fixing.
A catalyst was obtained in the same manner except that the temperature was changed to 0 ° C.

Comparative Example 1 Example 1 was placed in 500 ml of an aqueous solution containing 53.6 g of lanthanum nitrate.
100 g of γ-alumina used in the above was added, and the mixture was stirred well for 1 hour, then heated and evaporated to dryness. Next, this mixture was calcined in the air at 900 ° C. for 2 hours to obtain a catalyst support powder having a specific surface area of 110 m ² / g. This was wet-pulverized with a ball mill for 24 hours to obtain an average particle diameter of 0.5 μm.
% Slurry. Thereafter, an aqueous solution of tetraammineplatinum (II) nitrate was added to this slurry in the same manner as in Example 1, and the mixture was heated and kneaded, evaporated to dryness, dried, and calcined.
A 20-mesh granular supported platinum catalyst (platinum supported amount: 1 wt%) was obtained.

Comparative Example 2 Using the catalyst-supporting powder obtained in Comparative Example 1, a granular catalyst having a palladium-supporting amount of 3 wt% was obtained in the same manner as in Example 4.

Test Examples In order to evaluate the heat resistance of the catalysts of Examples 1 and 2, Comparative Examples 1 and 2, and Reference Examples 1 to 3, a combustion reaction test of carbon monoxide was performed under the following conditions. The heat resistance of the catalyst is 1,000 ° C3 in air compared to the activity immediately after catalyst preparation (initial activity).
Judgment was made based on the degree of activity decrease after heat treatment for 0 hours.

Catalyst: 10-20mesh granular catalyst, 2cc Reaction tube: Pyrex glass tube with inner diameter 20mm Gas composition: CO 3,500ppm O ₂ 17% (air base) Gas flow rate: 7.12l / min Space velocity: 105,000h- ¹ Also combustion reaction test Before starting, 200 ° C in dry air
Aged for 2 hours.

The results obtained are shown in FIG. FIG. 4 is a plot of the catalyst layer inlet temperature at a carbon monoxide combustion rate of 50% at the initial stage and after a heat treatment at 1,000 ° C. for 30 hours in order to compare the performances of the catalysts. It can be seen that the catalyst according to the present invention has a smaller decrease in the catalyst layer inlet temperature at a combustion rate of 50% than the conventional catalyst obtained in the comparative example, and is more excellent in heat resistance.

〔The invention's effect〕

According to the present invention, by selectively supporting a catalyst component on lanthanum aluminate, it is possible to provide a highly heat-resistant catalyst that can be used for a long time under a temperature condition of, for example, 1,000 ° C. or less. Further, in the present catalyst, an expensive precious metal component is effectively used, so that the economic effect is large.

[Brief description of the drawings]

FIG. 1 is a model explanatory view of a catalyst surface obtained by a conventional method,
FIG. 2 is an explanatory view of a surface model of the catalyst according to the present invention, FIG.
The figure shows the initial activity and the activity after 1,000 hours at 1,000 ° C. of the catalysts of Examples, Comparative Examples and Reference Examples. FIG.
The figure which plotted the catalyst layer entrance temperature at the time of 50% of carbon monoxide burning rate of each catalyst of an Example, a comparative example, and a reference example at the initial stage and after the heat treatment of 1,000 degreeC for 30 hours.

Claims (2)

(57) [Claims] 1. A method for producing a combustion catalyst comprising a refractory inorganic carrier as a first component, a lanthanum aluminate as a second component, and at least one noble metal selected from platinum and palladium as a third component. A method for producing a combustion catalyst, comprising: supporting the noble metal component on the lanthanum aluminate thus obtained, and coating the noble metal component on the surface of the refractory inorganic carrier as the first component. 2. The method according to claim 1, wherein lanthanum aluminate is prepared by reacting α-alumina with a lanthanum compound.