JPH0994436A - Exhaust gas purification catalyst and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a catalyst for easy oxidation of formaldehyde from methanol fuel by carrying Pt-Rh and Pd-Rh in a specified state on a honeycomb carrier of ceramics. SOLUTION: Oxidized metal powder 3b with Pt and Rh fixed and carried in the surface layer is bonded to a honeycomb carrier 3a made mainly of ceramics such as cordierite ceramics. Oxidized metal powder 3c with Pd and Rh fixed and carried in the surface layer is further bonded to the top of the bonded powder 3b. The noble metals are fixed and carried on the carrier by 0.1-10g, in total, per complete catalyst 11. When the resultant catalyst is used, formaldehyde discharge from an internal-combustion engine using methanol fuel is converted into gaseous CO2 and water by easy oxidation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst used in a catalytic converter for treating exhaust gas from an internal combustion engine using methanol as a fuel and a method for producing the same.

[0002]

2. Description of the Related Art As a countermeasure against air pollution (especially nitrogen oxide NO _x ), introduction of alcohol-blended gasoline or alcohol, 100% alcohol fuel, especially 100% methanol fuel into the internal combustion engine from the viewpoint of fuel economy. Is being considered recently. Under steady-state operation, methanol combines with oxygen in the air to produce carbon dioxide gas (CO ₂ ) and carbon monoxide gas (CO) as follows: 2CH ₃ OH + 3O ₂ → 2CO ₂ + 4H ₂ O 2CH ₃ OH + 2O ₂ → 2CO + 4H ₂ O However, immediately after the internal combustion engine starts to operate, a significant amount of methanol comes out of the combustion chamber in an unburned state as exhaust gas because the combustion temperature is low. The generated methanol is oxidized by the action of the catalyst, but its activity is slow because the catalyst itself is still at a low temperature. Therefore, methanol causes a reaction such as 2CH ₃ OH + O ₂ → 2HCHO + 2H ₂ O to formaldehyde (HCH
O) is easy to generate.

Formaldehyde is a colorless gas that is irritating and breathless at room temperature. Therefore, it is necessary to release it to the atmosphere after converting it into carbon dioxide gas, water, etc., like unburned methanol and carbon monoxide by a catalyst.

However, even with a monolith catalyst having rhodium, platinum and cordierite as a main active ingredient and cordierite as a carrier, which is currently evaluated to be capable of more efficiently converting nitrogen oxides, unburned methanol and carbon monoxide. ,
The conversion of formaldehyde is not sufficient.

[0005]

Therefore, an object of the present invention is to provide a catalyst capable of converting formaldehyde into carbon dioxide gas and water.

A further object of the present invention is to provide a catalyst which can easily oxidize formaldehyde emitted from an internal combustion engine using methanol fuel into carbon dioxide gas and water.

Another object of the present invention is to provide a catalyst capable of converting exhaust gas emitted from an internal combustion engine using methanol fuel into substantially harmless one.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that a catalyst comprising platinum and rhodium and palladium and rhodium supported in a specific state can achieve the above object. This has led to the completion of the present invention.

That is, according to the present invention, a metal oxide powder having platinum and rhodium fixedly supported on the surface layer is bonded to a honeycomb-shaped carrier body mainly made of ceramics, and further palladium and rhodium are fixedly supported on the surface layer. A metal oxide powder is bonded to the honeycomb-shaped carrier body, and the noble metal is added to the honeycomb-shaped carrier body in an amount of 0.
The present invention relates to an exhaust gas purifying catalyst used in a catalytic converter for treating exhaust gas from an internal combustion engine that uses methanol as a fuel, which carries 1 to 10 g.

Another aspect of the present invention further relates to an exhaust gas purifying catalyst, wherein the honeycomb carrier main body is composed of a porous body made of cordierite ceramics. The metal oxide powder preferably consists mainly of alumina. The metal oxide powder is preferably bound to the honeycomb-shaped carrier through a binder. Furthermore, the binder is preferably alumina sol, aluminum nitrate or talc.

The above-mentioned method for producing an exhaust gas purifying catalyst used in a catalytic converter for treating exhaust gas from an internal combustion engine using methanol as a fuel is a method for producing an exhaust gas purifying catalyst after immersing a metal oxide powder in an aqueous solution containing platinum and rhodium. A first step of pulling up and drying the powder, followed by firing to immobilize and support platinum and rhodium on the surface layer of the powder-constituting particles; after immersing another metal oxide powder in an aqueous solution containing palladium and rhodium The second step of pulling up and drying the powder, followed by firing to fix and support palladium and rhodium on the surface layer of the powder-constituting particles (however, even if the first step and the second step are performed at the same time, the second step is also performed). May be carried out first); the honeycomb-shaped carrier body mainly made of ceramic is mixed with the metal oxide powder in which platinum and rhodium produced in the first step are bonded on the surface layer of the particles. A third step in which the honeycomb-shaped carrier body is dried after being applied with a slurry consisting of powder and water, and subsequently fired to bond the metal oxide particles to the honeycomb-shaped carrier body; and platinum and rhodium are particles. The honeycomb-shaped carrier body in which the metal oxide particles bonded to the surface layer are fixedly supported is a slurry composed of the metal oxide powder having palladium and rhodium prepared in the second step bonded on the surface layer of the particles, a binder, and water. A fourth step of drying the honeycomb-shaped carrier body after the above, and subsequently firing the bonded particles to further bond the particles of the metal oxide powder onto the honeycomb-shaped carrier body;
Can be manufactured by

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention will be described in detail below.

The carrier body used in the present invention is a honeycomb carrier body mainly made of ceramics. Preferably, cordierite ceramics (2MgO.2Al
It is a porous body composed of ₂ O ₃ .5SiO ₂ ).

In the catalyst of the present invention, metal oxide particles having platinum and rhodium fixedly supported on the surface layer are bonded to the carrier body, and further metal oxide particles having palladium and rhodium fixedly supported on the surface layer are bonded thereto. The precious metal is supported on the honeycomb-shaped carrier body in a total amount of 0.1 to 10 g per 1 l of the finished catalyst. The metal oxide particles are preferably an alumina porous body,
More preferably, the BET surface area is 100 to 300 m ² /
g alumina porous body. Small bead-like alumina particles have long been used as a carrier for finely dispersed precious metal particles because of their high thermal stability and large surface area. Further, alumina particles may be mixed with up to about 40% by weight of ceria particles before use. Furthermore, silica,
It may coexist with a heat-resistant carrier such as magnesia, zirconia, and titania that provides sufficient strength as a carrier for finely dispersed precious metal particles.

The metal oxide particles are preferably bound to the honeycomb carrier body via a binder to strengthen the binding. The binder is preferably alumina sol, aluminum nitrate or talc.

Although the exact catalyst mechanism of the catalyst of the present invention is unknown, platinum acts as a catalyst at a low temperature to cause a reaction of 2CH ₃ OH + O ₂ → 2HCHO + 2H ₂ O to generate formaldehyde. It is considered that the palladium present in ₂₎ acts as a catalyst to cause a reaction of HCHO + O ₂ → CO ₂ + H ₂ O to convert formaldehyde into carbon dioxide gas.

The exhaust gas purifying catalyst used in the catalytic converter for treating exhaust gas from an internal combustion engine using methanol as a fuel is prepared by immersing metal oxide particle powder in an aqueous solution containing platinum and rhodium. Pull up and dry,
Subsequently, the first step of firing to fix platinum and rhodium on the surface layer of the powder-constituting particles is carried; and another metal oxide powder is dipped in an aqueous solution containing palladium and rhodium, and then the powder is pulled up and dried. Then, a second step in which the powder and the rhodium are fixed and supported on the surface layer of the powder-constituting particles by subsequent firing (however, the first step and the second step may be performed simultaneously or the second step may be performed first). ); A honeycomb carrier main body mainly made of ceramic is applied with a slurry composed of a metal oxide powder in which platinum and rhodium are bonded on the surface layer of powder constituent particles, a binder and water, and then the honeycomb carrier main body is dried. And a third step of subsequently firing to bond the particles of the metal oxide powder to the honeycomb-shaped carrier; and fixing the metal oxide powder having platinum and rhodium bonded on the surface layer of the powder constituent particles. The honeycomb-shaped carrier body thus obtained is subjected to a slurry consisting of metal oxide powder in which palladium and rhodium are bonded on the surface layer of the powder constituting particles, a binder and water, and then dried, followed by firing, and the metal oxide powder. And a fourth step in which the particles of 4 are further bonded onto the honeycomb-shaped carrier body.

Explaining each step in detail, in the first step, first, an aqueous solution containing a predetermined amount of platinum and rhodium is prepared. Usually, an inorganic salt, an organic salt, a metal acid or a salt thereof capable of forming an aqueous solution, in particular, a chloride, a nitrate, a metal chloride and various complex salts are dissolved in water to form, for example, a nitric acid acidic solution of a dinitrodiamino complex salt. To form an aqueous solution. The metal oxide powder is dipped in the aqueous solution prepared in this way. At this time, it is preferable to stir for several minutes so that the surfaces of the particles are completely and uniformly covered with platinum and rhodium (cations thereof). After mixing is complete, the powder is pulled up and dried at 100 ° C. for 5-10 hours to return to powder form. Subsequently, this powder was sieved to obtain -200 mesh, and the powder was subjected to 3 at 500 to 600 ° C. under a hydrogen atmosphere.
Calcination is carried out for about 5 hours to fix and support platinum and rhodium on the surface layer of the powder constituent particles. The firing temperature varies depending on the decomposition temperature of the noble metal-containing salt. Volatile components remaining by the calcination are dissipated, and platinum and rhodium are fixedly supported on the metal oxide particles. After this step, the BET surface area of the metal oxide particles is preferably 100-250 m ² / g.

Next, in the second step, an aqueous solution containing a predetermined amount of palladium and rhodium is prepared. This can be produced in the same manner as the aqueous solution containing platinum and rhodium in the first step. The metal oxide powder is immersed in the aqueous solution thus obtained. Also at this time, it is preferable to stir for several minutes so that the surfaces of the particles are completely and uniformly covered with (the cation of) palladium and rhodium. After mixing is complete, the powder is pulled up and dried at 100 ° C. for 5-10 hours to return to powder form. Subsequently, this powder was sieved to obtain -200 mesh, and the powder was subjected to 3 at 500 to 600 ° C. under a hydrogen atmosphere.
Firing is carried out for ~ 5 hours to immobilize and support palladium and rhodium on the surface layer of the powder constituent particles. The firing temperature varies depending on the decomposition temperature of the noble metal-containing salt. Volatile components remaining by the calcination are dissipated, and palladium and rhodium are fixedly supported on the metal oxide particles. After this step, the BET surface area of the metal oxide particles is preferably 100-250 m ^2.
/ G.

The above first step and second step may be carried out simultaneously, or the second step may be carried out first.

In the first step and the second step, finely dispersed noble metal particles, that is, metal oxide powder particles in which platinum and rhodium are fixedly supported on the surface and metal oxide powder particles in which palladium and rhodium are fixedly supported on the surface. After preparing, the particles, the binder and water are mixed to prepare a slurry. When an inorganic binder is used as a binder, the slurry contains particles, binder and water in weight%, particle: binder: water = 10.
It is preferably contained in a ratio of 0: 4: 80. When an organic binder is used as the binder, the particles, the binder and the water are represented by weight%, particle: binder: water =
It is preferably contained in a ratio of 100: 4: 80. The binder is preferably alumina sol, aluminum nitrate or talc. Mill until a substantially uniform slurry is obtained.

In the third step, first, the honeycomb-shaped carrier body is coated with the slurry containing platinum and rhodium prepared as described above. Specifically, it can be applied by immersing and pulling up the honeycomb-shaped carrier body in the slurry, brush coating the slurry on the body, or spray coating. Then, the honeycomb-shaped carrier body is heated at 100 ° C. for 5
Dry for 10 hours, then 500-60 under air atmosphere
The particles on which platinum and rhodium are fixedly supported are bonded to the honeycomb-shaped carrier body by firing at 0 ° C. for 3 to 5 hours.

Then, in the fourth step, the honeycomb-shaped carrier body is coated with the slurry containing palladium and rhodium prepared as described above. Various methods can be considered as described above. After that, it is dried at 100 ° C. for 5 to 10 hours, and then at 500 to 600 ° C. for 3 to 3 in an air atmosphere.
By firing for 5 hours, the particles on which palladium and rhodium are fixedly supported are bonded to the honeycomb-shaped carrier body.

It should be noted in the first step and the second step that the noble metal composed of platinum, palladium and rhodium is
0.1 liters per 1 liter of the finished catalyst (metal oxide powder and honeycomb carrier body) on the honeycomb carrier body.
The amount is adjusted so that 10 g is supported. The weight ratio of platinum to rhodium in the finely dispersed particles supporting platinum and rhodium is preferably 1: 1 to 50: 1. The ratio of palladium to rhodium in the finely dispersed particles supporting palladium and rhodium is preferably 1: 1 to 50: 1 by weight.

[0025]

The present invention will be described in more detail with reference to the following examples with reference to the drawings, but the present invention is not limited thereto.

Here, FIG. 1 is a perspective view showing a cylindrical exhaust gas purifying device 1 filled with a honeycomb-shaped exhaust gas purifying catalyst of the present invention, and FIG. 2 is a device shown in FIG. FIG. 3 is an enlarged schematic view of a cross section in the cylindrical direction of FIG. 3 is a schematic cross-sectional view of the catalyst shown in FIG. 2 taken along the line AA.

(Example) An exhaust gas purifying apparatus shown in FIGS. 2 and 3 was manufactured using the honeycomb-shaped exhaust gas purifying catalyst manufactured as follows.

The exhaust gas purifying apparatus 1 shown in FIG. 1 comprises a cylindrical outer cylinder 2 and a honeycomb-shaped exhaust gas purifying catalyst 3 shown in FIG. As shown in FIG. 3, the exhaust gas purification catalyst 3 has a honeycomb-shaped carrier body 3a.
And a catalyst 3b attached to the surface of the carrier body 3a and a catalyst 3b further attached thereon.

Here, the exhaust gas purifying catalyst 3 was manufactured according to the following steps.

[Preparation of catalyst] Palladium nitrate having a concentration of 0.23 g / l and 0.29
100 g of alumina porous particle powder having a BET surface area of 100 m ² / g was soaked in a mixed aqueous solution containing rhodium nitrate at a concentration of g / l, and the particle surface was sufficiently covered with palladium and rhodium (cations thereof). After stirring, the powder particles were pulled up and dried at 120 ° C. for 2 hours, and subsequently calcined at 600 ° C. for 1 hour in a hydrogen atmosphere to fix platinum and rhodium on the surface layer of the particles. And
The powder was mixed with an alumina sol binder and water. The mixing ratio is% by weight, powder: binder: water = 100:
It was 4:80. Then, it was ground using a ball mill until a substantially uniform slurry was obtained. At this time,
Methyl merulose was added as a dispersant.

Dinitrodiaminoplatinum (Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ) at a concentration of 0.32 g / l and 0.29 g / l
In a mixed aqueous solution containing rhodium nitrate at a concentration of 1
Then, 100 g of alumina porous particle powder having a BET surface area of 100 m ² / g, which is different from the above, was soaked and sufficiently stirred so that the particle surface was completely covered with platinum and rhodium (cation thereof),
After that, the powder particles are pulled up and dried at 120 ° C. for 2 hours,
Then, the mixture was baked in a hydrogen atmosphere at 600 ° C. for 1 hour to immobilize and support platinum and rhodium on the surface layer of the particles. Then, the powder was mixed with an alumina sol binder and water. Mixing ratio is weight%, powder: binder: water = 1
It was 00:04:80. Then, it was ground using a ball mill until a substantially uniform slurry was obtained. At this time, methyl merulose was added as a dispersant.

The honeycomb carrier body consisting essentially of cordierite ceramic is dipped in the slurry containing platinum and rhodium prepared in the above step, and then the honeycomb carrier body is pulled up and dried at 100 ° C. for 5 hours. Then, it was fired in an air atmosphere at 600 ° C. for 3 hours to bond the particles on which platinum and rhodium were fixedly supported to the honeycomb-shaped carrier body.

Subsequently, the honeycomb-shaped carrier main body was pulled up and dipped in the slurry containing palladium and rhodium prepared in the above step and dried at 100 ° C. for 5 hours, and subsequently, fired at 600 ° C. for 3 hours in an air atmosphere. Then, particles on which palladium and rhodium were fixedly supported were bonded to the honeycomb-shaped carrier body.

[Measurement of the prepared catalyst] The BET surface area of the catalyst prepared as described above was 10 m ² / g. In addition, a total of 2 g of noble metal composed of platinum, palladium, and rhodium was loaded on the honeycomb-shaped carrier body per 1 l of the finished catalyst.

Comparative Example A monolithic platinum-palladium / cordierite catalyst produced by a commercially available impregnation method was used as a comparative example. The precious metal was supported on the carrier in an amount of 2 g per 1 l of the finished catalyst.

(Test Example) Exhaust gas containing formaldehyde was passed through the exhaust gas purifying catalysts of the present invention produced in Examples and Comparative Examples at a flow rate of 12 l / min, and the resulting gas was analyzed.

As shown in FIG. 4, the conversion efficiency of formaldehyde was significantly higher for the catalysts of the examples than for the comparative examples. In addition, the conversion efficiency of unburned methanol and carbon monoxide contained in the exhaust gas was comparable to the conventional one. From these results, the exhaust gas purifying catalyst of the present invention can exhibit excellent effects over a wide range of catalyst inlet temperatures even when used as a catalytic converter for exhaust gas from an internal combustion engine that uses methanol as a fuel. It turns out that it is possible.

[0038]

The exhaust gas purifying catalyst of the present invention can effectively reduce the formaldehyde emitted from an internal combustion engine that uses methanol as a fuel.

[Brief description of drawings]

FIG. 1 is a perspective view showing a cylindrical exhaust gas purification device filled with a honeycomb-shaped exhaust gas purification catalyst of the present invention.

FIG. 2 is an enlarged schematic view of a cross section of the device shown in FIG. 1 in the cylindrical direction.

FIG. 3 is a schematic cross-sectional view of the catalyst shown in FIG. 2 taken along the line AA.

FIG. 4 is a diagram showing conversion rates of formaldehyde of the catalyst of the example of the present invention and the catalyst of the comparative example.

[Explanation of symbols]

 1: Exhaust gas purification device 2: Cylindrical outer cylinder 3: Exhaust gas purification catalyst 3a: Honeycomb-shaped carrier body 3b, 3c: Catalyst

Claims (6)

[Claims] 1. A honeycomb-shaped carrier body mainly made of ceramics, to which metal oxide particle powder having platinum and rhodium fixed and supported on the surface layer is bonded, and further, palladium and rhodium fixed and supported on the surface layer and oxidized. A metal particle powder is bonded, and the noble metal is added to the honeycomb-shaped carrier body in a total amount of 0.1 per 1 l of the finished catalyst.
An exhaust gas purifying catalyst for use in a catalytic converter for treating an exhaust gas from an internal combustion engine that uses methanol as a fuel, which is fixedly supported by 10 g. 2. The exhaust gas purifying catalyst according to claim 1, wherein the honeycomb-shaped carrier body is made of cordierite ceramics. 3. The exhaust gas purifying catalyst according to claim 1, wherein the metal oxide particles are mainly composed of an alumina porous body. 4. The exhaust gas purifying catalyst according to claim 1, wherein the metal oxide particles are bonded to the honeycomb-shaped carrier through a binder. 5. The binder is alumina sol, aluminum nitrate or talc.
The exhaust gas purifying catalyst according to 1. 6. A method for producing an exhaust gas purifying catalyst for use in a catalytic converter for treating exhaust gas from an internal combustion engine using methanol as a fuel, comprising immersing metal oxide particle powder in an aqueous solution containing platinum and rhodium. After that, the particle powder is pulled up and dried, and subsequently fired to carry platinum and rhodium fixedly supported on the surface layer of the particles; and another metal oxide particle powder in an aqueous solution containing palladium and rhodium. After soaking the powder, the particle powder is pulled up and dried, and subsequently baked to carry palladium and rhodium fixedly supported on the surface layer of the particles (however, if the first step and the second step are carried out at the same time, In addition, the second step may be performed first); the metal oxide is obtained by bonding the honeycomb-shaped carrier body mainly made of ceramics with platinum and rhodium produced in the first step on the surface layer of the particles. A third step of bonding the metal oxide particles to the honeycomb-shaped carrier body by drying the honeycomb-shaped carrier body after applying a slurry containing child powder, a binder, and water, and platinum and rhodium. A honeycomb-shaped carrier body in which metal oxide powder bonded to the surface layer of particles is fixedly supported,
Palladium and rhodium produced in the step is dried on the honeycomb-shaped carrier main body after applying a slurry consisting of metal oxide particle powder bonded on the surface layer of the particle, a binder and water, and subsequently fired to perform the oxidation. A fourth step of further bonding metal powder particles onto the honeycomb-shaped carrier body, wherein the noble metal is the finished catalyst 1l on the honeycomb-shaped carrier body.
A method for producing an exhaust gas purifying catalyst for use in a catalytic converter for treating an exhaust gas from an internal combustion engine using methanol as a fuel, characterized in that 0.1 to 10 g of the catalyst is supported in total.