JPS62106843A - Catalyst for purifying exhaust gas and its preparation - Google Patents

Abstract

PURPOSE:To enhance catalytic effect and to improve catalytic activity, by applying a catalytically active substance containing at least one platinum group element selected from Pt, Rh and Pd to the gas contact surface or gas contact part of a refractory three-dimensional structure so as to form projections. CONSTITUTION:An activated alumina pellet is impregnated with an aqueous solution containing a water-soluble salt to one or more of a catalytically active component comprising a platinum group element selected from Pt, Rh and Pd to support said component and the impregnated pellet is dried, baked and subsequently ground by a hammer mill to obtain a catalytically active substance supported powder which is, in turn, thrown in an aqueous solution containing a dispersant to prepare a slurry under stirring. This slurry is infiltrated in a three-dimensional structure and the excessive slurry is subsequently removed from said three-dimensional structure to form a largely depressed and protruded projection-like catalyst coating layer to the internal wall surfaces of said struc ture or the surface of the skeletal thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a catalyst for purifying diesel engine exhaust gas or industrial exhaust gas containing combustible carbon particles, and a method for producing the same. 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 become a problem in terms of environmental health. . 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, inspections are underway to tighten regulations on the emission of these particulates from diesel engines and other sources.

By the way, methods for removing these fine particles can be broadly classified into the following two methods. 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, the burner One method is to regenerate the filter by burning off the particulates accumulated in the filter, and the other is to reduce the frequency of this heat-resistant gas fill, or to increase the combustion activity of the catalyst to the point where 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 is employed that effectively maintains catalytic activity under the emission conditions (gas composition and temperature) of diesel engine exhaust gas.

However, the exhaust gas temperature of diesel engines is much lower than that of gasoline engines, and the exhaust gas purification catalyst described above has the ability to successfully ignite and burn accumulated particulates within the temperature that can be obtained under normal engine running conditions. Despite this requirement, no catalyst has been proposed to date that meets this requirement.

(Prior Art) Various proposals have been made for the purpose of increasing the trapping effect of carbonaceous fine particles. Attempt to increase the trapping effect of carbonaceous particles by adhering heat-resistant inorganic fibers to the inner wall of the through-hole of a structure having through-holes (Japanese Patent Application Laid-Open No. 59142820
(Japanese Unexamined Patent Application Publication No. 1987-1999), or an attempt to capture carbonaceous particles by providing a large number of irregularly arranged projections on the inner wall of a ceramic honeycomb structure having through holes
99314) Furthermore, by attaching coarse ceramic particles to an oven honeycomb or wall flow honeycomb or foaming the wall surface to create protrusions, drying and firing can be performed to create a carrier that enhances the carbonaceous 111 trapping effect. It has been proposed (Japanese Unexamined Patent Publication No. 58-14
Publication No. 921).

Further, examples of using platinum group gold layers as carbonaceous particulate combustion catalysts include rhodium 7.5%/platinum alloys, P[/Pd = 50150 mixtures, and catalysts supported on tantalum oxide or cerium oxide. Palladium or an alloy consisting of palladium and platinum with a maximum weight of 75% or less is
It has been proposed that this method is effective against (Japanese Unexamined Patent Publication 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 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), carbon-based particulate purification catalyst* containing vanadium or a vanadium compound in combination with antimony, alkali metals, molybdenum, platinum, lanthanum, etc.
(Japanese Unexamined Patent Publication No. 1982-82944), carbon-based particulate purification catalyst consisting of a combination of copper or copper compound with molybdenum or vanadium, and further with platinum, rhodium, etc. Carbon-based particulate purification catalyst whose ability to generate sulfate was suppressed by heat treatment with
JP-A-59-36543), carbon-based particulate purification catalyst comprising a combination of palladium and at least one of rhodium, ruthenium, nickel, zinc and titanium (JP-A-59-80330), etc. being done.

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 possible to propose a practical catalyst that has low-temperature ignition performance by supporting the catalyst in the form of protrusions, and by imparting mechanical strength to the shape.

[Problems to be Solved by the Invention] The present inventors hereby propose a catalyst that can burn carbonaceous particles contained in exhaust gas from a diesel engine at a lower temperature, and a method for adjusting the catalyst.

The 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 even below 300'C, combustion of carbonaceous particles is possible. Catalysts with good performance are 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. The present invention has been completed by discovering that the catalyst performance can be significantly improved by increasing the contact efficiency of carbonaceous fine particles.

[Means for solving problems] The present invention is specified as follows.

(1) A refractory structure in which a catalytically active substance containing at least one platinum group element consisting of platinum, rhodium, and palladium is formed in the shape of a protrusion on the gas contacting surface or gas contacting part of the refractory three-dimensional structure. A catalyst for purifying exhaust gas, characterized in that it is supported on an organic inorganic base material.

(2) At least one platinum group element consisting of platinum, rhodium, and palladium and iron, cobalt, nickel, molybdenum, tungsten, niobium, phosphorus, lead, and zinc on the gas contact surface or gas contact part of the refractory three-dimensional structure. ,tin,
Contains at least one selected from the group consisting of alkaline earth metals such as copper, manganese, cerium, lanthanum, silver, barium, magnesium, calcium, and strontium, and alkali metals such as potassium, sodium, cesium, and rubidium. 1. A catalyst for purifying exhaust gas, comprising a catalytically active substance supported on a refractory inorganic base material formed into protrusions.

(3) The catalyst according to (1) or (2) above, wherein the refractory three-dimensional structure is a ceramic foam, a ceramic honeycomb, a wall-flow type honeycomb monolith, a metal honeycomb, or a metal foam.

(4) The refractory inorganic base material is selected from the group consisting of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, and zeolite. The catalyst according to (1), (2) or (3) above, characterized in that it is at least one type of catalyst.

(5) Coarse particles made of a fire-resistant type R base material supporting a catalytically active substance are at least selected from the group consisting of alumina sol, titania sol, zirconia sol, silica sol, soluble boehmite, and soluble organic polymer compound. Exhaust gas purification characterized by forming an aqueous slurry with one type of dispersant and using the slurry obtained to support the coarse particles in the form of protrusions on the gas contacting surface or gas contacting part of a refractory three-dimensional structure. Production method of catalyst for use.

(6) The catalyst according to (5) above, wherein the refractory three-dimensional structure is a ceramic foam, a ceramic honeycomb, a wall-flow type honeycomb monolith, a metal honeycomb, or a metal foam.

Carbon-based fine particles accumulate in a layered manner in the gas-contacting part of a three-dimensional structure, such as a wall-flow type honeycomb (consisting of a large number of flow pipes in the gas flow direction, the flow pipes having alternately open inlets, 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 that has 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 pore entrance side wall surface and accumulate in a layer on the gas population side partition wall surface. If a platinum group element-containing catalyst is placed on the partition wall surface or the aggregate in the partition wall pores,
When supported in layers without forming protrusions,
The contact efficiency of the catalytically active component with the accumulated carbon-based fine particles is poor, and no favorable catalytic action is 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 to increase the contact efficiency and to significantly improve the combustion efficiency of carbon-based fine particles.

As the three-dimensional structure, ceramic foam, ceramic honeycomb, wall flow type honeycomb monolith, metal honeycomb, metal foam, etc. are suitably 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.

Although the method for preparing the catalyst according to the present invention is not specified, the following method is preferred as an example.

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 fired. Next, a hammer mill (for example, PLILVER manufactured by Hosokawa Micron Co., Ltd.
IXER), and the crushed product is classified using a classifier (for example, MICRON 5EPARATOR, MS-0 type, manufactured by Hosokawa Micron Co., Ltd.), and the fire resistance of the culm is substantially distributed in the particle size range of 5μI11 to 300μIll. A catalytically active material, DISPURAL manufactured by Fuba-Condea Co., Ltd., in which a catalyst component such as a platinum group element is supported on inorganic coarse particles, is added to an aqueous solution containing 1 to 20% by weight in terms of alumina (Al2O2) and stirred. Due to the thickening effect of boehmite as a dispersant, the particulate active substance does not settle and a stable slurry can be obtained not only during stirring but even after stirring is stopped.

By supporting the slurry on a three-dimensional structure and removing excess slurry, a protruding catalyst coating layer with large irregularities can be formed on the inner wall surface of the v4m body or on the skeleton surface. Next, dry at 200-800℃, especially at 30℃.
Alumina, titania, zirconia, which have a thickening effect to prevent coarse particles from settling when heated from 0°C to 700°C.
It can be used by forming an aqueous slurry together with a sol such as silica, soluble boehmite, and at least one dispersant selected from the group consisting of soluble organic polymer compounds. , ammonium polyacrylate, sodium salt or ammonium salt of acrylic acid-maleic acid copolymer,
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, rock wool, 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 addition, as a preparation method suitable for the present invention, a granular heat-resistant inorganic substance (having the same particle size as above) is supported on a three-dimensional structure, and an aqueous solution or an organic solvent soluble solution of the catalytically active component is prepared. A salt solution may be impregnated and supported to become a catalyst.

In the catalyst according to the present invention, the catalytically active component supported is not particularly limited, but is in the range of 10 to 200 g, preferably 20 to 150 g, per 1 Jl of catalyst as coarse particles defined by the present invention. As the heat-resistant inorganic base material, 5 to 150 (I preferably 1
The amount of the catalytically active component as an oxide or metal is in the range of 0.01 to 50 g, preferably 0.05 to 30 g, per 1 Jl of catalyst.

Effect] 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 A commercially available activated alumina pellet (3 to 5IIIllφ, surface area 150 butts/g) was weighed out, and platinum (Pt)
The sample was supported by immersion in 750 m of an aqueous solution of dinitrodiammine platinum in nitric acid containing 20 g of dinitrodiammine platinum, dried at 150°C for 3 hours, and calcined at 500°C for 2 hours.

The fired pellets were pulverized with a hammer mill, and particles with a size of 5 μm or less were cut with a 2-classifier, and particles with a size of 300 μm or more were removed using a sieve.

The particle size distribution of the obtained powder catalyst was 5 to 30 μm and 11% by weight.
, 30-45 μm 14 weight 1%, 45-740 m 20
Weight 11%, 74-105μm 241ffi%, 10
It had a particle size distribution of 5 to 149 m, 15% by weight, 149 to 30 m, 16% by weight, and an average particle diameter of 81 m.

150 g of the classified powder catalyst was dispersed in an aqueous solution prepared by dissolving 15 g of soluble boehmite (11.2!M in terms of Af203) to obtain 520 m of stable slurry.

The viscosity of this slurry was 22 cps ('! temperature).

As a carrier, a commercially available plug honeycomb (material: cordierite) 5.66 inch diameter x 6. 0 inch length, 100 cells/inch square, and 17 mil wall thickness. The average pore diameter of the partition walls of the carrier was 28 μm. Pour the slurry 520d from the side of the gas inlet of the carrier,
Excess slurry was removed by air blowing from the opposite side. Then, it was dried at 150℃ for 3 hours, and then dried in air at 500℃ for 2 hours.
A complete catalyst was obtained by calcination for several hours.

The finished carrier of each component is Al2O250Q/Jl
-Support, Pt 1. O(J/i, -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 A nitric acid solution of dinitrodimain platinum containing 15 (J)
Supported by immersion in a mixed solution of rhodium nitrate aqueous solution containing 1.670% as rhodium (Rh), and heated to 150°C.
The mixture was dried 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. The classified powder catalyst 1 was added to an aqueous solution prepared by dissolving soluble boehmy 1 to 100a (AJ!, 75 g in terms of 203) in advance.
A stable slurry of 2 Jl was obtained by dispersing Kl.

The viscosity of this slurry was 72 cps (room temperature). As a carrier, a commercially available oven honeycomb monolith (material: cordierite), 5.66 inch diameter x 6.0 inch length, 3
00 cells/in² and a wall thickness of 6 mils.

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 finished catalyst. The amount of each component supported in the finished product is A1203 120 (J/L-
Support, Pt 0.9Q/f-support, Rh 0.1(1
/J-1 carrier.

Example 3 Cerium nitrate<Ce (N
Oa > 3 ・6H20) 630.7g of aqueous solution a50Ai! Impregnated with. It was dried for 150'03 hours and fired at 500°C for 2 hours. Next, 4? , P [as dinitrosia ζ containing 25a) Platinum in nitric acid solution 750. d. It was dried for 150'03 hours and fired at 500°C for 2 hours.

Pulverize and classify in the same manner as in Example 1 to obtain an average particle size of 7.
A powder catalyst containing a catalyst of 9 μm was obtained. The classified powder catalyst 150i11 was dispersed in advance in an aqueous solution containing 15 g of silica sol (manufactured by Snowtex-O Kabuto Kagaku) in terms of 5 iOz to obtain a stable slurry 520d. A support similar to that in Example 1 was used for catalysis. Finished carrier for each component 1HtA, 1, 20340a /1-111
body, CeO210g/f-support, Pt1. It was an Oa/E carrier.

Example 4 In Example 2, instead of the oven honeycomb monolith as a carrier, a commercially available ceramic foam (with a bulk density of 0.
35a/cm3. Porosity 87.5%, volume 1.71)
All catalysts were prepared in the same manner except that The amount of each component supported in the finished product is Af203120 (1/,!,
-Support, Pt O, 9g/l -Support, ri'h O,l
a/1-carrier.

Example 5 A catalyst having the catalyst composition shown in Table 1 below was obtained in the same manner as in Examples 1 to 4.

Here, ammonium baramolybdate 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.

Example 6 Pt-supported alumina powder catalyst 15 prepared in Example 1
(Af
203 equivalent 11.25a) was dissolved in an aqueous solution to obtain a stable slurry 520, which was catalyzed.

The amount of each component supported in the finished product is Af2035007・'℃
-Support, Pt 1. Og/l-carrier, SiC whisker 3.31 J/4-carrier.

Comparative Example 1 A PT-supported alumina pellet prepared in the same manner as in Example 1 was pulverized, and then wet pulverized in a wet mill to the extent that a conventional 4-tooth coating was applied to obtain an average particle size of 1.1.
A slurry with a diameter of 520 µm was prepared. The catalyst was prepared in the same manner except that it was used in Example 1, and Δ7 color 20350111/, 1
．． -Support, pt i, OQ/'1-Support, supported catalyst was obtained.

Comparative Example 2 In the same manner as in Example 2, pt, F? The h-supported alumina pellets were pulverized, and then wet pulverized in a wet mill to the extent that a normal wash coat 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 amount of each component supported in the finished product is Afz 031200/
- Color carrier, P [0,9 g/l - carrier, I? hO,i/
, color-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 a He1203 supported oven honeycomb monolith was prepared.

Comparative Example 4 In Example 3, instead of using 630.79 of cerium nitrate, chromium nitrate [Cr(NOg)3.91-12
The catalyst was prepared in the same manner except that 01 was used as 1316(l), and the amount of each component supported was AJ!, 20340(
1/J! , - carrier, Cr20310g/J! , - carrier,
It was Pt 1 , Og, /1-113 body.

Regarding the catalysts obtained in practical side layer Examples 1 to 6 and Comparative Examples 1 to 4,
A catalyst evaluation test was conducted using a 4-cylinder diesel engine with an exhaust capacity of 12,300 cc. Engine speed 2
Particles were captured for about 2 hours under the conditions of 50 rpm, torque 4.0, and 9 m, and then the torque was increased to 0.57 rg.
The change in pressure drop in the catalyst layer was continuously recorded by raising the pressure every 5 minutes at m intervals, and as the exhaust gas temperature rose on the catalyst, the pressure increased due to accumulation of fine particles and the pressure decreased due to combustion of fine particles. When the temperature becomes equal to <Te), ignition and combustion occur,
The temperature fff(Ti) at which the pressure drop drops sharply was determined. In addition, when capturing fine particles with 2500 ppm, l~silk, OKg・m, the change in pressure drop over time is calculated from the chart by the amount of change in pressure drop per hour, and ΔP (sH(+ /H
I found the (direct) of r ).

Also, 250Orpm, t-lux 4. Using a dilution tunnel under OKg-TrL fine particle trapping conditions, the fine particle matrix at the catalyst inlet and outlet was measured to determine the fine particle capture rate (%). These results are shown in Table 2.

Table 2

Claims (7)

[Claims] (1) A refractory structure in which a catalytically active substance containing at least one platinum group element consisting of platinum, rhodium, and palladium is formed in the shape of a protrusion on the gas contacting surface or gas contacting part of the refractory three-dimensional structure. A catalyst for purifying exhaust gas, characterized in that it is supported on an organic inorganic base material. (2) At least one platinum group element consisting of platinum, rhodium, and palladium and iron, cobalt, nickel, molybdenum, tungsten, niobium, phosphorus, lead, and zinc on the gas contact surface or gas contact part of the refractory three-dimensional structure. , tin, copper,
A catalyst containing at least one selected from the group consisting of an alkaline earth metal consisting of manganese, cerium, lanthanum, silver, barium, magnesium, calcium, and strontium, and an alkali metal consisting of potassium, sodium, cesium, and rubidium. A catalyst for purifying exhaust gas, characterized in that an active material is supported on a refractory inorganic base material formed into protrusions. (3) Claim (1) or (2), 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. catalyst. (4) The refractory inorganic base material is selected from the group consisting of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, and zeolite. Claims (1), (2) or (3) characterized in that at least one type
Catalysts as described. (5) Coarse particles made of a refractory inorganic base material supporting a catalytically active substance are at least one type 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. (6) The catalyst according to claim (5), wherein the refractory three-dimensional structure is a ceramic foam, a ceramic honeycomb, a wall-flow type honeycomb monolith, a metal honeycomb, or a metal foam. (7) Claim (5) or (7) characterized in that an inorganic fibrous material is mixed into coarse particles made of a refractory inorganic base material supporting a catalytically active material to form a slurry.
6) Method described.