JPH074528B2 - Method for producing catalyst for purifying exhaust gas from internal combustion engine using alcohol as fuel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to unreacted alcohol, carbon monoxide (CO), and hydrocarbons that are harmful substances to be stepped on in exhaust gas from an internal combustion engine that uses alcohol as a fuel. The present invention relates to a method for producing an exhaust gas purifying catalyst for detoxifying and decomposing (HC) and aldehydes, and particularly to a method for producing a catalyst having excellent low-temperature decomposition performance for aldehydes. Is.

In recent years, the problem of environmental pollution due to exhaust gas from internal combustion engines has become serious, and in order to solve this problem and from the viewpoint of diversifying energy sources, the use of alcohol such as methanol and ethanol as fuel for internal combustion engines provides energy Attempts have been made to use these alcohols as fuels for internal combustion engines from the two viewpoints of stabilizing the fuel.

However, when alcohol is used as a fuel for an internal combustion engine,
It is known that the amount of aldehydes in exhaust gas is many times that of gasoline or light oil.
When aldehydes are released into the atmosphere without being treated, odors and irritation to mucous membranes of the human body due to high concentration of aldehydes are very serious problems. Furthermore, photooxidation reaction occurs with nitrogen oxides in the atmosphere, causing photochemical smog. Aldehydes are extremely problematic substances in terms of air pollution.

Thus, there is a need for development of a purification catalyst and a method for producing the same for completely burning unreacted alcohol, HC, CO, and aldehydes, or for decomposing them and releasing them as pollution-free gas.

<Prior Art> As an exhaust gas purifying catalyst for an internal combustion engine using alcohol such as methanol or ethanol as fuel, aluminum oxide in which palladium is lattice-stabilized with an alkaline earth metal oxide and / or an oxide of a lanthanide group element is used. A method for producing a catalyst has been proposed which is characterized by using it. (JP Sho
(JP-A-58-79544) In addition, a method for producing a catalyst for purifying exhaust gas from an internal combustion engine is proposed, in which silver is used as an active ingredient, and what is dispersed and carried on a washcoat base material is used as fuel for methanol carried on a structure. . (U.S. Pat. No. 4,304,761) However, none of them disclose a catalyst having a good low temperature activity as intended by the present invention, and a great difference from the level of practical use is recognized.

<Problems to be Solved by the Invention> Certainly, cleaner energy is required due to the problem of environmental pollution due to gas discharged from an internal combustion engine of an automobile or the like, and alcohol is attracting attention as a fuel source. However, when alcohol is used as fuel, unreacted alcohol, CO, HC and aldehydes remain in the exhaust gas,
In particular, high concentrations of aldehydes cause irritating odors and photochemical smog. Degradation and removal of these aldehydes is a very important issue from an environmental viewpoint. Moreover, no method has yet been proposed for producing an effective catalyst capable of decomposing and removing these unreacted alcohols, CO, HC, and aldehydes even when the exhaust gas temperature is low as seen during engine idling to render them harmless. The current situation.

<Means for Solving the Problems> The inventors of the present invention have conducted intensive studies to address the above-mentioned problems. As a starting material, dinitrodiammine platinum was used as a starting material, and platinum was used alone or platinum was used as a main component, and palladium or rhodium was further combined therewith. The resulting catalytically active substance is dispersed and supported on a porous inorganic base material and is preferably used in an oxidizing atmosphere such as air.
The present invention has completed a method for producing a catalyst that oxidizes and decomposes unreacted alcohol, CO, HC, and aldehydes at a lower temperature by heat treatment at 600 to 900 ° C to render them harmless. That is, using dinitrodiammine platinum as a starting material, preferably 600 ~ 9 as a firing temperature in an oxidizing atmosphere.
When heat-treated at 00 ° C, preferably 700 to 850 ° C, the method for producing the obtained catalyst has a remarkable low-temperature oxidative decomposition activity of unreacted alcohols and aldehydes, which has not been found in the conventional platinum group catalysts. That is the reason why the present invention has been completed. The present invention is specified as follows.

(1) Using dinitrodiammine platinum as a starting material,
After supporting this on a porous refractory inorganic substrate,
A method for producing a catalyst for purifying exhaust gas from an internal combustion engine that uses alcohol as a fuel, characterized by being heat-treated at a temperature in the range of 600 to 900 ° C.

(2) The porous refractory inorganic base material is activated alumina,
Silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-zirconia, titania-zirconia, and at least one selected from the group consisting of zeolite, and its shape is pellet-like or porous. The manufacturing method according to (1) above, wherein the inner wall surface of the fire-resistant three-dimensional structure is formed into a coat layer.

(3) The manufacturing method according to (2) above, wherein the porous refractory three-dimensional structure is made of ceramic foam, ceramic honeycomb, wall flow type honeycomb monolith, metal honeycomb, or metal foam.

(4) The porous refractory inorganic base material is made of activated alumina, platinum is contained in an amount of 0.2 to 5.0 g per 1 of the catalyst, and a platinum-containing alumina coat layer is formed on the refractory three-dimensional structure. The manufacturing method according to (1) above.

(5) The manufacturing method according to (1) above, wherein the heat treatment temperature is in the range of 700 to 850 ° C.

(6) Dinitrodiammine platinum is used as a platinum source, and at least one compound selected from the group consisting of palladium and rhodium is added to Pt / (Pd + Rh).
= 1 to 40 (atomic ratio), the catalytically active substance contained in the range is dispersed and supported on the porous refractory inorganic base material, and then 60
A method for producing a catalyst for purifying exhaust gas from an internal combustion engine that uses alcohol as a fuel, characterized by being heat-treated at a temperature in the range of 0 to 900 ° C.

(7) The porous refractory inorganic base material is activated alumina,
Silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-zirconia, titania-zirconia, and at least one selected from the group consisting of zeolite, and its shape is pellet-like or porous. The manufacturing method according to (6) above, wherein the inner wall surface of the fire-resistant three-dimensional structure is formed into a coat layer.

(8) The method according to (7) above, wherein the porous refractory three-dimensional structure is made of ceramic foam, ceramic honeycomb, wall flow type honeycomb monolith, metal honeycomb, or metal foam.

(9) The porous refractory inorganic base material is made of activated alumina, platinum is contained in an amount of 0.2 to 5.0 g per 1 of the catalyst, and a platinum-containing alumina coat layer is formed on the refractory three-dimensional structure. The manufacturing method according to (6) above.

(10) The manufacturing method according to (6) above, wherein the heat treatment temperature is in the range of 700 to 850 ° C.

The amount of platinum supported in the method for producing the catalyst of the present invention is 0.2 to 5.0 g, preferably 0.5 to 4.0 g per catalyst 1 as a metal element.
Is the range. The starting material for platinum is specified to be dinitrodiammine platinum. Further, as starting materials for palladium, palladium nitrate, palladium chloride,
Palladium tetramine chloride and palladium sulfide complex salt are preferable, and palladium nitrate is particularly preferable. The starting materials for rhodium are rhodium nitrate, rhodium chloride, hexaaminorhodium chloride, rhodium sulfide complex salts and rhodium sulfate, with rhodium nitrate being particularly preferred.

The porous inorganic base material on which the catalytically active component is dispersed and supported is composed of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia and zeolite. At least one selected from the group is used, and the shape thereof is a pellet form or a powder form thereof is made into an aqueous slurry and wash-coated on a refractory three-dimensional structure to form a coat layer for use.

When used as a pellet-shaped carrier, the shape is not particularly limited as long as it is a granular carrier. For example, it may be columnar, columnar, spherical, crushed, etc., and preferably has an average particle size in the range of 2.0 to 5.0 mm. The method for preparing the catalyst according to the present invention is specifically described as follows.

The above-mentioned porous inorganic substance such as activated alumina is wet-slurried into a fire-resistant three-dimensional structure such as a cordierite honeycomb monolith, wash-coated, the excess slurry is removed, dried, and calcined, and the alumina-coated three-dimensional structure is catalytically activated. The catalyst is prepared by immersing and supporting in a solution containing a white metal element as a component, drying at 150 ° C. to 300 ° C., and calcining in air at 600 to 900 ° C., preferably 700 to 850 ° C. for 1 to 10 hours.

As another method, for example, activated alumina powder is loaded with the above-mentioned platinum group element in advance, dried at 150 to 300 ° C., and then 60
Firing is performed in the air at 0 to 900 ° C, preferably 700 to 850 ° C for 1 to 10 hours. Then, the slurry is made into a slurry by a wet mill, and for example, a honeycomb monolith carrier is wash-coated, excess slurry is removed, dried, and calcined at 350 to 500 ° C. for 1 to 10 hours to prepare a catalyst. When using a pelletized inorganic base material,
After impregnating with a solution of a platinum group metal compound, it is dried at 150 to 300 ° C and air is 600 to 900 ° C, preferably 1 to 10 at 700 to 850 ° C.
Bake for hours to obtain the finished catalyst.

The method for preparing the catalyst of the present invention is not limited to these methods, and the method for preparing the catalyst of the present invention can be prepared by various preparation methods as long as it does not violate the gist thereof.

<Operation> When alcohol such as methanol or ethanol is used as a fuel in an internal combustion engine of an automobile or the like, the formation of aldehydes becomes a particular problem as described above, and in the case of a vehicle which is a mobile source, parking at idling If the aldehydes are released as they are, it is expected that the pedestrians in the surrounding area will be seriously damaged. Especially, a catalyst having a high resolution of harmful substances is required even in an idling state where the exhaust gas temperature is low.

However, a platinum raw material other than dinitrodiammine platinum, for example, a catalyst is prepared using chloroplatinic acid or the like, or 400 to 500 ° C. which is proposed as a method for preparing an ordinary platinum-based catalyst.
The heat-treated product had poor decomposition activity for unreacted alcohols and aldehydes at low temperature (140-160 ℃) and showed a high aldehyde residual rate, and its pungent odor was intolerable.

As a result of intensive studies, we have found that a catalyst containing a platinum group element using dinitrodiammine platinum as a platinum source is preferably 600 to 900 ° C., preferably 700 to 700 ° C. in an oxidizing atmosphere.
By heat treatment at ~ 850 ℃, unreacted alcohol,
The inventors have found a catalyst system having an excellent ability to oxidize and decompose aldehydes, especially at low temperatures. The following two factors are conceivable as the factors that could bring out the better low-temperature activity.

One is using dinitrodiammine platinum in an oxidizing atmosphere.
When heat-treated at 600 to 900 ° C, preferably 700 to 850 ° C, it was found that the dispersed and supported platinum particle diameters were almost uniform in the range of 100 Å to 500 Å when observed with a transmission electron microscope. The detoxification of HC, oxygen-containing compounds, and especially the unreacted alcohol and aldehydes could be controlled within the range of particle size effective for oxidative decomposition reaction at low temperature.

The other is that no ordinary anion, such as chlorine or sulfur, which is used in the case of using a conventional platinum-containing compound such as chloroplatinic acid or a platinum sulfide complex, remains in the catalytically active substance. Is.

Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples of the present invention.

Example 1 Commercially available cordierite honeycomb monolith carrier (105.
100 g of activated alumina powder slurried in 3 mmφ × 115.0 mm ^L , 300 cells / square inch) was supported as alumina. Next, the activated alumina layer-forming monolith carrier was immersed in 1000 ml of a nitric acid acidic aqueous solution of dinitrodiammineplatinum containing 2.0 g of platinum metal (Pt) for 1 hour to adsorb Pt to the activated alumina layer. This was dried at 150 ° C for 3 hours and then fired in air at 800 ° C for 2 hours. The supported amount of Pt is catalyst 1
The Pt per hit was 2.0 g. Observation of the obtained catalyst with a transmission electron microscope revealed that the particle diameters were almost uniform between 200 Å and 350 Å.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that the calcination temperature was 600 ° C. for 2 hours. Pt loading per catalyst
It was 2.0 g as Pt.

Example 3 A catalyst was prepared in the same manner as in Example 1 except that the calcination temperature was 900 ° C. for 2 hours. Pt loading per catalyst
It was 2.0 g as Pt.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that the calcination temperature was 500 ° C. for 2 hours. The amount of Pt supported was 2.0 g as Pt per catalyst. Many of the obtained catalysts had a platinum particle size of 100Å or less.

Comparative Example 2 A catalyst was prepared in the same manner as in Example 1 except that the calcination temperature was 1,050 ° C. for 2 hours. The amount of Pt supported was 2.0 g as Pt per catalyst. In the obtained catalyst, many coarse particles having a platinum particle size of 500 Å or more were observed.

Example 4 Commercially available cordierite honeycomb monolith carrier (105.
150 g of activated alumina powder slurried into 3 mmφ × 115.0 mm, 300 cells / square inch) was coated and supported as alumina.

Next, the activated alumina layer was formed on a mixture of 500 ml of nitric acid acidic aqueous solution of dinitrodiammine platinum containing 3.64 g of platinum metal (Pt) and 500 ml of nitric acid acidic aqueous solution of palladium nitrate containing 0.36 g of palladium metal (Pd). The monolith carrier was immersed for 1 hour to adsorb Pt and Pd on the activated alumina layer. After drying at 150 ℃ for 3 hours, baking temperature is 850
Baking for 2 hours in air at 0 ° C. The supported amount of Pt and Pd is catalyst 1
The amounts were 3.64 g and 0.36 g, respectively.

Example 5 A commercially available cordierite ceramic foam carrier (bulk density: 0.35 g / cm ³ , porosity: 87.5%, volume: 1) was coated with 100 g of a silica-alumina powder slurry.

Next, 500 ml of an aqueous nitric acid solution of dinitrodiammineplatinum containing 0.15 g of platinum metal (Pt) and an aqueous solution of palladium nitrate containing 0.05 g of palladium metal (Pd) 500.
The silica-alumina layer-forming ceramic foam carrier is immersed in a mixed solution of 1 ml for 1 hour to form a silica-alumina layer with Pt.
And Pd were adsorbed. This was dried at 150 ° C. for 3 hours and then fired at 800 ° C. in air for 2 hours. The amounts of Pt and Pd supported were 0.15 g and 0.05 g per catalyst, respectively.

Example 6 1 kg of activated alumina powder was added to a nitric acid acidic aqueous solution 1 of dinitrodiammineplatinum containing 15 g of platinum, mixed well, dried at 150 ° C. for 5 hours, and then calcined at 800 ° C. in air for 2 hours. A powder containing Pt was obtained.

The powder was slurried in a wet mill, supported on a cordierite honeycomb monolith carrier having the same specifications as used in Example 1, dried at 150 ° C for 3 hours, and further dried at 400 ° C for 1 hour.

The amount of Pt supported on the obtained catalyst was 1.5 g of Pt per 1 catalyst.

Example 7 Commercially available cordierite honeycomb monolith carrier (105.3 m
150 g of alumina-zirconia powder slurried in mφ × 115.0 mm ^L , 300 cells / square inch) was supported.

Next, dinitrodiammine platinum containing 2.0 g of platinum metal (Pt) in 500 ml of nitric acid acid solution and rhodium metal (Rh)
1 g of the alumina-zirconia layer-forming monolith carrier was mixed with 500 ml of an aqueous rhodium nitrate solution containing 0.2 g of
It was immersed for a time, and Pt and Rh were adsorbed on the alumina-zirconia layer. After drying this at 150 ℃ for 3 hours, baking temperature in air 8
It was baked at 00 ° C for 2 hours. The loaded amounts of Pt and Rh were 2.0 g and 0.2 g, respectively, per catalyst.

Example 8 In Example 1, 500 ml of nitric acid acidic aqueous solution of dinitrodiammine platinum containing 3.0 g of platinum metal (Pt), 250 ml of palladium nitrate aqueous solution containing 0.5 g of palladium metal (Pd), and 0.1 g of rhodium metal (Rh). A catalyst was prepared by the same method except that a mixed solution of 250 ml of an aqueous rhodium nitrate solution was used, and Pt3.0 g and Pd0.5 per catalyst 1 were prepared.
g and Rh 0.1 g of the supported catalyst was obtained.

Example 9 Spherical alumina carrier manufactured by Rhone-Poulin (average particle size 2.8 m
m, BET surface area 100 m ² / g, apparent specific gravity 0.43 g / ml, total pore volume 1.2 ml / g) 430 g of Pt as 1 g, Pd as 0.1 g containing dinitrodiammine platinum nitric acid aqueous solution and palladium nitrate aqueous solution After being added to 500 ml of the mixed solution of and impregnated,
Concentrate with hot air until the surface is dry, then at 150 ° C for 2
After drying for an hour, the product was baked in air at 800 ° C. for 2 hours.

Comparative Example 3 A catalyst was prepared in the same manner as in Example 1 except that the nitric acid acidic aqueous solution of dinitrodiammine platinum was replaced with a chloroplatinic acid aqueous solution, and a catalyst having a supported amount of Pt of 2.0 g per catalyst 1 was obtained.

<Performance Measurement> A] Each catalyst obtained in Examples 1 to 9 and Comparative Examples 1 to 3 was 24.0 mmφ × 300 mm ^L (catalyst amount 14 ml) with a diamond cutter.
After cutting into 25.5mmφ × 300mm ^L stainless steel reaction tube, methanol 0.1% by volume, formaldehyde 0.1% by volume, water 10% by volume, oxygen 10% by volume, carbon monoxide 0.5% by volume, remaining nitrogen is contained. Gas was introduced under the conditions of S.V50,000Hr ^-1 , catalyst layer inlet gas temperature 140 ° C and 160 ° C, and inlet gas,
The concentrations of methanol and formaldehyde in the outlet gas were analyzed. The conversion rate of methanol was calculated from the following formula, and formaldehyde was shown in Table 1 as the outlet gas concentration.

The analysis of methanol was carried out by FID gas chromatography, and the analysis of formaldehyde was carried out by colorimetric analysis using chromotropic acid.

B] Each catalyst obtained in Examples 1 to 9 and Comparative Examples 1 to 3 was 24.0 mmφ × 30 mm ^L (catalyst amount 14 ml) with a diamond cutter.
Cut into 25.5 mmφ × 300 mm ^L stainless steel reaction tubes, and then a gas containing 0.1% by volume of ethanol, 0.1% by volume of acetaldehyde, 0.2% by volume of carbon monoxide, 10% by volume of water, 0.7% by volume of oxygen, and the remaining nitrogen. Was introduced under the conditions of S.V50,000Hr ^-1 , catalyst layer inlet gas temperature of 160 ° C and 200 ° C, and inlet gas,
The concentrations of ethanol and acetaldehyde in the outlet gas were analyzed, the conversion rate of ethanol was calculated from the following formula, and the acetaldehyde concentration was shown in Table 2 as the outlet gas concentration.

The analysis of ethanol and acetaldehyde was carried out using FID gas chromatography.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B01J 23/44 ZAB A 8017-4G 23/46 ZAB 8017-4G 311 A 8017-4G

Claims (10)

[Claims] 1. An alcohol, characterized in that dinitrodiammine platinum is used as a starting material, which is dispersed and supported on a porous refractory inorganic base material, and then heat-treated at a temperature in the range of 600 to 900 ° C. And a method for producing a catalyst for purifying exhaust gas from an internal combustion engine. 2. The porous refractory inorganic substrate is selected from the group consisting of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-zirconia, titania-zirconia, and zeolite. Consisting of at least one selected,
The method according to claim (1), characterized in that the shape is pelletized or the inner wall surface of the porous fire-resistant three-dimensional structure is in the form of a coat layer. 3. The porous refractory three-dimensional structure comprises a ceramic foam, a ceramic honeycomb, a wall flow type honeycomb monolith, a metal honeycomb, or a metal foam, according to claim (2). Production method. 4. A porous refractory inorganic base material made of activated alumina, containing 0.2 to 5.0 g of platinum per 1 part of the catalyst, and forming a platinum-containing alumina coat layer on the refractory three-dimensional structure. The manufacturing method according to claim (1), which is characterized. 5. The manufacturing method according to claim 1, wherein the heat treatment temperature is in the range of 700 to 850 ° C. 6. Dinitrodiammine platinum is used as a platinum source, and at least one compound selected from the group consisting of palladium and rhodium is added to Pt / (Pd
+ Rh) = 1-40 (atomic ratio) The catalytically active substance contained in the range is dispersed and supported on the porous refractory inorganic base material, and then heat-treated at a temperature in the range of 600 to 900 ° C. A method for producing a catalyst for purifying exhaust gas from an internal combustion engine that uses alcohol as a fuel. 7. The porous refractory inorganic substrate is selected from the group consisting of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-zirconia, titania-zirconia, and zeolite. Consisting of at least one selected,
The manufacturing method according to claim (6), characterized in that the shape thereof is a pellet shape or the inner wall surface of the porous fire-resistant three-dimensional structure is formed as a coat layer. 8. The porous refractory three-dimensional structure comprises a ceramic foam, a ceramic honeycomb, a wall flow type honeycomb monolith, a metal honeycomb, or a metal foam, according to claim 7. Production method. 9. A porous refractory inorganic base material comprising activated alumina, wherein platinum is contained in an amount of 0.2 to 5.0 g per 1 of the catalyst, and a refractory three-dimensional structure is provided with a platinum-containing alumina coat layer. The manufacturing method according to claim 6, which is characterized in that. 10. The manufacturing method according to claim 6, wherein the heat treatment temperature is in the range of 700 to 850 ° C.