JPH0568301B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a catalyst for purifying diesel engine exhaust gas or industrial exhaust gas containing combustible carbon particles. In recent years, particulate matter (mainly composed of solid carbon particles, sulfur-based particles such as sulfates, and liquid or solid high-molecular-weight hydrocarbon particles) in diesel engine exhaust gas has tended to become an environmental health problem. . This is because most of these fine particles have particle diameters of 1 micron or less and are easily suspended in the atmosphere and easily taken into the human body through breathing. Therefore, consideration is being given to tightening regulations on the emission of these particulates from diesel engines and the like. By the way, the methods for removing these fine particles are as follows:
There are two main methods as follows. One is to filter exhaust gas using a heat-resistant gas filter (ceramic foam, wire mesh, metal foam, wall-flow type ceramic honeycomb, etc.) to capture fine particles, and if the pressure drop increases, they will accumulate in burners, etc. Another method is to reduce the frequency of the above-mentioned combustion regeneration by carrying a catalyst substance on a carrier having a heat-resistant gas filter structure and performing a combustion process along with the filtration operation. This is a method of increasing the combustion activity of the catalyst to such an extent that regeneration is not necessary. In the former case, the higher the particle removal effect, the faster the pressure drop increases and the frequency of regeneration increases, which is cumbersome and economically disadvantageous. In comparison, the latter method is considered to be a much better method if a catalytic material that can effectively maintain catalytic activity under the exhaust conditions (gas composition and temperature) of diesel engine exhaust gas is employed. However, the exhaust gas temperature of diesel engines is much lower than that of gasoline engines.
Despite the need for an exhaust gas purification catalyst that has the ability to successfully ignite and burn accumulated particulates within the temperature range found under normal engine running conditions, no method of manufacturing a catalyst that satisfies this condition has been proposed until now. The current situation is that this has not been done. (Prior Art) Various proposals have been made for the purpose of increasing the trapping effect of carbonaceous fine particles. An attempt was made to bond heat-resistant inorganic fibers to the inner walls of the through-holes of a structure having through-holes to increase the capture effect of carbonaceous particles (Japanese Unexamined Patent Publication No. 142820/1982), or the inner wall of a ceramic honeycomb structure having through-holes. An attempt was made to supplement carbonaceous fine particles by providing a large number of irregularly arranged protrusions on the honeycomb (Japanese Patent Application Laid-open No. 57-99314).Also, an attempt was made to attach coarse ceramic particles to an open honeycomb or wall flow honeycomb, or to foam the wall surface. A method for manufacturing a carrier has been proposed in which the effect of trapping carbonaceous particles is enhanced by forming protrusions, followed by drying and firing (Japanese Unexamined Patent Publication No. 14921/1983). Rhodium
SOF (soluble
It has been proposed that this method is effective against organic fraction (Japanese Patent Application Laid-Open No. 55-24597). In addition, at least one supported material selected from the group consisting of noble metals, chromium and catalytically active compounds of these and elements of the first transition series, silver, hafnium and catalytically active compounds of these A composition comprising a catalytically effective amount of a mixture of at least one bulk material selected from the group consisting of compounds, the supported material being supported on a porous refractory inorganic oxide. (Japanese Unexamined Patent Publication No. 57-24640), a method for manufacturing carbon-based particulate purification catalysts in which vanadium or vanadium compounds are combined with antimony, alkali metals, molybdenum, platinum, lanthanum, etc. (Japanese Unexamined Patent Publication No. 58-174236) ), a method for producing a carbon-based particulate purification catalyst made by combining copper or a copper compound with molybdenum or vanadium, and further combining platinum, rhodium, etc.
59-82944), Method for producing carbon-based particulate purification catalyst in which platinum is supported and heat treated at 700 to 1000°C to suppress sulfate generation ability (Japanese Patent Application Laid-Open No. 1983-36543), palladium, rhodium, ruthenium, Method for producing a catalyst for purification of carbon-based fine particles comprising a combination of at least one of nickel, zinc, and titanium
80330) and other proposals have been made. However, the present inventors have found that when platinum group elements are used as combustion catalysts for carbon-based fine particles, the catalysts disclosed in these documents do not fully bring out the low-temperature ignitability of carbon-based fine particles possessed by platinum group elements. found it difficult. In other words, in order to bring out the low-temperature ignitability of carbon-based fine particles possessed by platinum group elements, a contact support layer is required to increase the contact efficiency with respect to the carbon-based fine particles that accumulate in a layer at the gas contact surface or contact portion of exhaust gas. The inventors have discovered that it is necessary to support the catalyst in the form of protrusions, and that by imparting mechanical strength to the shape, it is possible to propose a method for producing a practical catalyst that has low-temperature ignition performance. [Problems to be Solved by the Invention] The present inventors have specifically identified carbonaceous particles contained in exhaust gas from diesel engines as
We propose a method for producing a catalyst that can be burned at lower temperatures. The method for producing a catalyst according to the present invention is highly evaluated for the following points. As mentioned above, the exhaust gas temperature from a diesel engine is much lower than that of a gasoline car, and the exhaust gas temperature during city driving does not reach 450°C even at the manifold outlet, so the combustion performance of carbonaceous particles is low even below 300°C. A good catalyst is required. However, in the catalysts containing platinum group that have been proposed so far, catalyst components are supported in a layered manner with fine particles in the gas contacting part of a three-dimensional structure, or supported on the inner wall surface of the internal pores of the aggregate. At present, sufficient combustion performance cannot be extracted from the catalytically active material containing the platinum group due to poor contact efficiency with captured carbonaceous fine particles. Therefore, the present inventors focused on the fact that carbonaceous fine particles accumulate in a layer on the wall surface of the gas contacting part or the gas contacting part, and by supporting the coarse particles of the catalytically active component in the accumulation layer in the form of protrusions, the catalyst The present invention has been completed by discovering that the catalyst performance can be significantly improved by increasing the contact efficiency between carbonaceous particles and carbonaceous fine particles. [Means for solving the problems] The present invention is specified as follows. (1) Coarse particles made of a refractory inorganic base material supporting a catalytically active substance are mixed with at least one kind selected from the group consisting of alumina sol, titania sol, zirconia sol, silica sol, soluble boehmite, and soluble organic polymer compound. A catalyst for exhaust gas purification, characterized in that the coarse particles are formed into an aqueous slurry with a dispersant, and the resulting slurry is used to support the coarse particles in the form of protrusions on the gas contact surface or gas contact portion of a refractory three-dimensional structure. Manufacturing method. (2) The method according to (1) above, wherein the fire-resistant three-dimensional structure is a ceramic foam, a ceramic honeycomb, a wall-flow type honeycomb monolith, a metal honeycomb, or a metal foam. (3) The method described in (1) above, wherein a catalytically active substance containing at least one platinum group element consisting of platinum, rhodium, and palladium is supported on a refractory inorganic base material formed in protrusions. manufacturing method. (4) At least one platinum group element consisting of platinum, rhodium, and palladium, and iron, cobalt, nickel, molybdenum, tungsten, niobium, phosphorus, lead, zinc, tin, copper, manganese, cerium,
Protruding catalytic active material containing at least one selected from the group consisting of alkaline earth metals such as lanthanum, silver, barium, magnesium, calcium, and strontium, and alkali metals such as potassium, sodium, cesium, and rubidium. The manufacturing method according to (1) above, wherein the method is supported on a refractory inorganic base material formed in a shape. Carbon-based fine particles accumulate in a layered manner in the gas-contacting part of a three-dimensional structure, for example, a wall-flow type honeycomb (consisting of a large number of flow pipes in the gas flow direction, the flow pipes having inlet ports open alternately, A ceramic monolith consisting of a flow pipe that is closed at the outlet, and a flow pipe that is closed at the inlet and open at the outlet, and the wall of the flow pipe is composed of a porous partition wall with a gas filter mechanism. honeycomb)
There are many pores in the partition walls of the pores, and when gas passes through these pores, carbon-based fine particles are filtered out, but even though the average diameter of the pores is much larger than the diameter of the carbon-based fine particles, The system fine particles form a bridge on the side wall surface of the pore entrance and accumulate in a layer on the partition wall surface on the gas inlet side. If the platinum group element-containing catalyst is supported in a layered manner on the partition wall surface or the aggregate in the partition wall pores without forming protrusions, the contact efficiency of the catalytically active component with the carbon-based fine particle accumulation will be No favorable catalytic action was observed. Therefore, the present invention is characterized in that a catalyst composition containing a platinum group element is supported in the gas contacting part of the three-dimensional structure in the form of protrusions, thereby increasing the contact efficiency and significantly improving the combustion efficiency of carbon-based fine particles. . As a three-dimensional structure, ceramic foam,
Ceramic honeycombs, wall-flow type honeycomb monoliths, metal honeycombs, metal foams, etc. are preferably used. Examples of refractory inorganic base materials supporting catalyst components such as platinum group elements include activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, and titania-zirconia. , zeolite, etc. are suitable. The method for producing the catalyst according to the present invention will be exemplified below as a specific procedure. That is, activated alumina pellets are impregnated with an aqueous solution of a water-soluble salt of a catalytically active component, and then dried and calcined. Next, the product is crushed with a hammer mill (for example, PULVERIXER manufactured by Hosokawa Micron Co., Ltd.), and the crushed product is passed through a classifier (for example, MICRON manufactured by Hosokawa Micron Co., Ltd.).
SEPARATOR, MS-O type) to classify, 5μm
A catalytically active substance-supported powder is obtained in which a catalyst component such as a platinum group element is supported on refractory inorganic coarse particles having a particle size substantially distributed in the range of ~300 μm. Next, the granules are added to an aqueous solution containing 1 to 20% by weight of soluble boehmite (for example, CONDEA, DISPURAL) in terms of alumina (Al ₂ O ₃ ) and stirred. Due to the thickening effect of boehmite as a dispersant, a stable slurry can be obtained without the granular active substance settling during stirring or even after stirring is stopped. By using the slurry to support a three-dimensional structure and removing excess slurry, a protruding catalyst coating layer with large irregularities can be formed on the inner wall surface or skeleton surface of the structure. Then dry 200
Calcinate at a temperature of ~800°C, especially 300°C to 700°C. In this preparation method, in order to prevent the coarse particles from settling when slurrying the coarse particles, a sol such as alumina, titania, zirconia, silica, etc., which has a thickening effect, soluble boehmite, and a soluble organic polymer compound is selected. The soluble organic polymer compound can be used by forming an aqueous slurry together with at least one dispersant. Examples of the soluble organic polymer compound include sodium polyacrylate, ammonium polyacrylate, sodium salt of acrylic acid-maleic acid copolymer, or Ammonium salts, polyethylene oxide, polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, starch, gum arabic, guar gum, glue and the like are preferably used.
In addition, inorganic fibrous substances such as glass fiber, alumina fiber, silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), potassium titanate, and rock wool are added to the slurry in order to improve the supporting strength of the coarse particulate catalyst active component. etc. may be dispersed. Further, in order to make the catalyst coat layer more porous, a method of adding a soluble organic polymer compound such as polyethylene glycol to the slurry and removing it by baking may be used in combination. In the method for producing a catalyst according to the present invention, the amount of catalyst active components supported is not particularly limited, but the amount of supported catalyst active components is 10 per catalyst as coarse particles defined by the present invention.
~200g, preferably 20-150g. As the heat-resistant inorganic base material, 5
~150g Preferably in the range of 10-120g, the catalytically active component being 0.01 per catalyst as an oxide or metal
~50g, preferably 0.05-30g. [Operation] The combustion reaction of carbonaceous particles is a solid-solid reaction, and the contact efficiency between the catalytically active substance and the carbonaceous particles is a very important factor. In view of this point, the present invention has an effect in that the activity is significantly improved by supporting the catalyst particulate material in a protruding manner on the side wall surface of the gas inlet and actively increasing the contact efficiency. EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples of the present invention. Example 1 1 kg of commercially available activated alumina pellets (3 to 5 mmφ, surface area 150 m ² /g) was weighed out, immersed in 750 ml of an aqueous solution of dinitrodiammine platinum in nitric acid containing 20 g of platinum (Pt), and supported at 150°C. It was dried for 3 hours and fired at 500°C for 2 hours. The fired pellets are pulverized with a hammer mill, and a particle size of 5 μm or less is cut with a classifier, and a particle size of 300 μm or less is
Those with a particle size of m or more were removed using a sieve. The particle size distribution of the obtained powder catalyst was 11% by weight of 5-30μm, 14% by weight of 30-45μm, 20% by weight of 45-74μm,
74-105μm 24% by weight, 105-149μm 15% by weight,
It had a particle size distribution of 149 to 300 μm, 16% by weight, and an average particle size of 81 μm. 15g of soluble boehmite (Al ₂ O ₃ equivalent)
150 g of the classified powder catalyst was dispersed in an aqueous solution obtained by dissolving 11.25 g of the classified powder catalyst to obtain 520 ml of stable slurry. The viscosity of this slurry was 22 cps (room temperature).
As a carrier, commercially available plug honeycomb (material: cordierite) 5.66 inch diameter x 6.0 inch length, 100
Cells per square inch and 17 mil wall thickness were used.
The average pore diameter of the partition walls of the carrier was 28 μm. The above slurry is poured from the side of the gas inlet of the carrier.
520 ml was poured and the excess slurry was removed by air blowing from the other side. The catalyst was then dried at 150°C for 3 hours and calcined in air at 500°C for 2 hours to obtain a complete catalyst. The amount of each component supported in the finished product is Al ₂ O ₃ 50g/
- carrier, Pt1.0g/- carrier. It was observed that this catalyst formed protrusions of coarse particles on the wall surface of the carrier without clogging the pores. Example 2 2 kg of commercially available activated alumina pellets (3 to 5 mmφ surface area 150 m ² /g) were weighed and mixed with a nitric acid solution of dinitrodiammine platinum containing 15 g of Pt and a rhodium nitrate aqueous solution containing 1.67 g of rhodium (Rh). It was supported by immersion in mixed solution 1.4, dried at 150°C for 3 hours, and fired at 500°C for 2 hours. The powder was pulverized and classified in the same manner as in Example 1 to obtain a Pt;Rh supported powder catalyst having an average particle size of 78 μm. 100g of soluble boehmite (Al ₂ O ₃
A stable slurry 2 was obtained by dispersing 1 kg of the classified powder catalyst in an aqueous solution obtained by dissolving 75 g of the classified powder catalyst. The viscosity of this slurry was 72 cps (room temperature).
The support used was a commercially available open honeycomb monolith (cordierite material) 5.66 inch diameter x 6.0 inch length, 300 cells/inch square, and 6 mil wall thickness. The carrier was immersed in the slurry, pulled out, and excess slurry was removed by air blowing. The catalyst was then dried at 150°C for 3 hours and calcined in air at 500°C for 2 hours to obtain a completed catalyst. The amount of each component supported in the finished product is
Al ₂ O ₃ 120g/- carrier, Pt 0.9 g/- carrier,
Rh was 0.1 g/− carrier. ^Example 3 Cerium nitrate (Ce
750 ml of an aqueous solution containing 630.7 g of (NO ₃ ) ₃・6H ₂ O)
Impregnated with. It was dried at 150°C for 3 hours and fired at 500°C for 2 hours. Then, it was impregnated with 750 ml of a nitric acid solution containing 25 g of dinitrodiammine platinum as Pt.
It was dried at 150°C for 3 hours and fired at 500°C for 2 hours. The powder was pulverized and classified in the same manner as in Example 1 to obtain a catalyst-containing powder catalyst having an average particle size of 79 μm. 150 g of the classified powder catalyst was dispersed in advance in an aqueous solution containing 15 g of silica sol (Slowtex-O, manufactured by Nissan Chemical) in terms of SiO ₂ to create a stable slurry of 520 ml.
I got it. A support similar to that in Example 1 was used for catalysis. The amount of carrier for each component in the finished product is
Al ₂ O ₃ 40g/- carrier, CeO ₂ 10 g/- carrier,
Pt1.0g/- carrier. Example 4 In Example 2, commercially available ceramic foam (bulk density 0.35 g/cm ³ , porosity 87.5%, volume 1.7) was used instead of the open honeycomb monolith as the carrier.
) All catalysts were prepared in the same manner except that they were used. The finished amount of each component supported is Al ₂ O ₃ 120g/
- carrier, Pt 0.9 g/- carrier, Rh 0.1 g/- carrier. Example 5 In the same manner as in Examples 1-4, Table 1 below
A catalyst with the catalyst composition shown below was obtained. Here, ammonium paramolybdate was used for molybdenum, ammonium dihydrogen phosphate was used for phosphorus, ammonium paratungstate was used for tungsten, niobium pentachloride was used for niobium, and nitrate was used for all others.

【table】

[Table] * Shows the molar ratio of oxides.
Example 6 150 g of the Pt-supported alumina powder catalyst obtained in Example 1 and 10 g of commercially available SiC whiskers were mixed with 15 g of soluble boehmite in advance in the same manner as in Example 1.
(11.25 g in terms of Al ₂ O ₃ ) was dissolved in an aqueous solution to obtain 520 ml of stable slurry, which was then catalyzed. The amount of each component supported in the finished product is Al ₂ O ₃ 50g/-
Support, Pt1.0g/-support, SiC whisker 3.3
g/- carrier. Comparative Example 1 Pt-supported alumina pellets prepared in the same manner as in Example 1 were pulverized, and then wet pulverized in a wet mill to the extent that a normal wash coating was performed to prepare a slurry with an average particle size of 1.1 μm. , 520ml of slurry was obtained. Catalysts were prepared in the same manner as in Example 1, except that 50 g of Al ₂ O ₃ per support and 1.0 g of Pt per support were obtained. Comparative Example 2 Pt, Rh prepared in the same manner as in Example 2
The supported alumina pellets were pulverized and then wet pulverized in a wet mill to the extent that a normal wash coating could be applied to prepare a slurry having an average particle size of 1.0 μm. An open honeycomb monolith supported catalyst was obtained using the slurry. The supported amount of each component in the finished product is Al ₂ O ₃ 120g/carrier, Pt 0.9g/-carrier,
RhO was 0.1 g/− carrier. Comparative Example 3 A catalyst was prepared in the same manner as in Example 2 except that Pt and Rh were not used, and an open honeycomb monolith supporting Al ₂ O ₃ was prepared. Comparative Example 4 In Example 3, chromium nitrate [Cr(NO ₃ ) ₃ ·9H ₂ O] was used instead of using 630.7 g of cerium nitrate.
A catalyst was prepared in the same manner except that 1316 g of Pt was used, and the amount of each component supported in the finished product was 40 g of Al ₂ O ₃ /- support, 10 g of Cr ₂ O ₃ /- support, and 1.0 g of Pt /- support. Example 7 The catalysts obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated using a 4-cylinder diesel engine with a displacement of 2300 c.c. Particulate capture was carried out for approximately 2 hours under the conditions of engine rotation speed 2500 rpm and torque 4.0 kg・m, and then the torque was
The change in pressure drop in the catalyst layer was continuously recorded by raising the pressure at 0.58 kg/m intervals every 5 minutes, and as the exhaust gas temperature rose on the catalyst, the pressure increased due to accumulation of fine particles and the pressure due to combustion of fine particles. The temperature at which the drop is equal (Te) and the temperature at which ignition and combustion occur and the pressure drop drops rapidly (Ti) were determined. In addition, the value of ΔP (mmHg/Hr) was calculated by calculating the change in pressure drop per hour from a chart when capturing fine particles at 2500 rpm and a torque of 4.0 Kg·m. In addition, using a dilution tunnel under particle capture conditions of 2500 rpm and 4.0 kg・m torque,
The amount of fine particles at the catalyst inlet and outlet was measured to determine the trapping rate (%) of fine particles. These results are shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1. Coarse particles made of a refractory inorganic base material supporting a catalytically active substance are selected from the group consisting of alumina sol, titania sol, zirconia sol, silica sol, soluble boehmite, and soluble organic polymer compound. An exhaust gas characterized in that it is made into an aqueous slurry with at least one type of dispersant, and the resulting slurry is used to support the coarse particles in the form of projections on the gas contacting surface or gas contacting portion of a refractory three-dimensional structure. Manufacturing method for purification catalysts. 2. The manufacturing method according to claim 1, wherein the fire-resistant three-dimensional structure is a ceramic foam, a ceramic honeycomb, a wall-flow type honeycomb monolith, a metal honeycomb, or a metal foam. 3. A catalytically active substance containing at least one platinum group element consisting of platinum, rhodium, and palladium is supported on a refractory inorganic base material formed into protrusions. Manufacturing method. 4 At least one platinum group element consisting of platinum, rhodium, and palladium, and iron, cobalt, nickel, molybdenum, tungsten, niobium, phosphorus,
Lead, zinc, tin, copper, manganese, cerium, lanthanum, silver, barium, magnesium, calcium,
A refractory inorganic base formed in the form of protrusions of a catalytically active material containing at least one selected from the group consisting of alkaline earth metals such as strontium, and alkali metals such as potassium, sodium, cesium, and rubidium. The manufacturing method according to claim 1, which comprises supporting on a material.