JP4329467B2 - Catalyst carrier and method for producing the same - Google Patents

Description

  The present invention relates to a monolithic catalyst carrier used in an exhaust gas purification apparatus in an internal combustion engine, and more particularly to a monolithic catalyst carrier that improves catalyst warm-up performance when the internal combustion engine is started.

Exhaust gas from an internal combustion engine such as an automobile engine contains substances such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO _x ). Discharging exhaust gas containing these components as it is causes pollution and environmental degradation, and is restricted by public regulations. Therefore, these components are discharged after being purified by an exhaust purification device that holds the catalyst.

For this purpose, exhaust purification catalysts such as three-way catalysts and NO _x storage reduction catalysts are used. Both of these exhaust gas purifying catalyst, CO is a component in the exhaust gas, HC, and purify NO _x, helps to CO _2, H ₂ O and N _2.

  In the use of these exhaust purification catalysts, the catalyst support layer is coated on a catalyst carrier such as a ceramic honeycomb, and the exhaust purification catalyst is supported on this catalyst support layer, whereby the exhaust to be purified contacts the catalyst. The area is increased to improve efficiency. In this regard, as shown in Patent Documents 1 and 2, it has also been proposed to introduce macropores in the catalyst support layer, thereby further promoting the contact between the exhaust purification catalyst supported on the catalyst support layer and the exhaust gas. .

  Specifically, in Patent Document 1, in order to increase the pore volume of the catalyst support layer by introducing macropores, a hardly soluble and non-water-absorbing powder solid component such as polyethylene powder, polypropylene powder, polystyrene powder, etc. It is proposed to coat a catalyst carrier with a coating slurry of a carrier layer material powder to which is added, and to dry and calcine it.

  Patent Document 2 proposes that the surface of the ceramic carrier is coated with a slurry containing activated alumina, and this is freeze-dried and fired.

  As described in Patent Documents 1 and 2, if macropores are introduced into the catalyst support layer supporting the exhaust purification catalyst and the pore volume of the catalyst support layer is increased, the diffusion of exhaust gas in the catalyst support layer And can prevent clogging of the pores in the catalyst support. Furthermore, this enhances the heat insulating property of the catalyst support layer, that is, the heat retaining property, so that it is also useful for maintaining the catalyst at a temperature higher than the catalyst activation temperature regardless of fluctuations in the operating state.

However, the introduction of macropores into the catalyst support layer and / or the increase in the pore volume of the catalyst support layer is caused by the increase in the heat insulation of the catalyst support layer. Delays warm-up of Since the exhaust purification catalyst generally works effectively only at a relatively high temperature (for example, more than 300 ° C.) and purifies substances such as HC, CO, NO _x in the exhaust, the delay in warming up the catalyst support layer is The initial purification rate of exhaust is reduced. In recent years, this is a problem because regulations regarding exhaust emissions, particularly regulations regarding emissions of HC at the start of automobile engines, have become stricter.

JP-A-57-144030 Japanese Examined Patent Publication No. 3-66015

  Accordingly, there is a need for a catalyst carrier that improves catalyst warm-up at the time of starting an internal combustion engine while maintaining the benefits of the prior art.

The monolith honeycomb catalyst carrier of the present invention has a high density carrier layer with a porosity of 40% or less on the upstream side of the exhaust flow and a low density carrier layer with a porosity of 50% or more on the downstream side of the exhaust flow. Here, the terms “high density support layer” and “low density support layer” mean that the porosity of the “high density support layer” is smaller than the porosity of the “low density support layer”. This porosity can be measured, for example, using a mercury porosimeter.

  The high density support layer on the upstream side of the exhaust flow is likely to be warmed by the exhaust heat, and therefore promotes warming up of the catalyst support layer from a low temperature such as when the engine is started. This is useful for demonstrating catalytic activity at an early stage and increasing the exhaust purification rate. Further, the low density support layer on the downstream side of the exhaust flow promotes the diffusion of exhaust gas in the catalyst support layer, prevents clogging of pores in the catalyst support, and further enhances the heat retention of the catalyst support layer.

In one aspect of the present invention, the porosity of the dense supporting layer, 25% or less, 20% or less, especially.

In one aspect of the present invention, the porosity of the low density supporting layer, 6 0% or more, especially 65% or more.

  In one embodiment of the invention, the low density support layer has macropores, ie pores with a diameter of 0.05 μm or more, in particular 0.1 μm or more.

  In one aspect of the invention, the dense support layer is present over 5-50% of the catalyst support length.

  The present invention also includes forming a high-density support layer by coating a catalyst support with a slurry containing a support layer material powder finer than the support layer material powder for the low-density layer and firing the catalyst support. It is a manufacturing method of the monolith type catalyst carrier of the present invention.

  Furthermore, the present invention provides a low-density carrier by coating a catalyst carrier with a slurry containing a surfactant selected from the group consisting of a glycerin fatty acid ester and a polyglycerin fatty acid ester, and a carrier layer material powder, followed by firing. It is the manufacturing method of the monolith type catalyst support of this invention including making a layer.

  According to the present invention, there is provided a monolith type catalyst carrier that improves the catalyst warm-up property when starting an internal combustion engine.

  In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings are diagrams schematically showing the catalyst carrier of the present invention, and the present invention is limited to these embodiments. is not.

  FIG. 1 is a view showing one embodiment of the monolith type catalyst carrier of the present invention. The catalyst carrier 10 which is a honeycomb carrier has an exhaust flow upstream portion 12 coated with a high density carrier layer and an exhaust flow downstream portion 14 coated with a low density carrier layer having macro holes. Here, the arrow 18 indicates the exhaust flow direction flowing into the catalyst carrier 10.

  2 (a) and 2 (b) respectively show honeycomb cells of an exhaust flow upstream portion 12 coated with a high density support layer and an exhaust flow downstream portion 14 coated with a low density support layer having macropores. It is sectional drawing seen from the exhaust flow direction. Here, the high-density support layer 24 or the support layer 26 having macropores is coated on the cell wall 22 of the honeycomb cell. It is also shown that the high density carrier layer 24 is relatively dense and the low density carrier layer 26 having macropores is relatively coarse.

  Below, each part which comprises the catalyst carrier of this invention is demonstrated concretely.

  The catalyst carrier may be a honeycomb carrier, for example a ceramic honeycomb carrier such as a cordierite honeycomb carrier or a metal honeycomb carrier.

  The high-density support layer can be obtained by any method for making a support layer having a desired porosity, but a support layer material such as alumina or zirconia is pulverized with a grinder such as a ball mill or an attritor, It can also be obtained by coating the catalyst carrier and calcining it.

  For the production of a low density carrier layer, particularly a low density carrier layer having macropores, the methods described in Patent Documents 1 and 2 can be referred to. Therefore, as in Patent Document 1, for example, a catalyst carrier is coated with a coating slurry of a carrier layer material powder to which a solid component that is hardly soluble and non-water-absorbing, such as polyethylene powder, polypropylene powder, and polystyrene powder, is added. Can be dried and fired to produce a support layer having macropores. Further, as in Patent Document 2, the surface of the catalyst carrier can be coated with a slurry containing activated alumina, and this catalyst carrier can be freeze-dried and fired to produce a support layer having macropores.

  The low density carrier layer is coated on the catalyst carrier with a slurry containing a surfactant selected from the group consisting of glycerin fatty acid esters and polyglycerin fatty acid esters and carrier layer material powders such as alumina, zirconia, and ceria zirconia. And it can manufacture by baking this. Here, examples of the glycerin fatty acid ester include stearic acid, oleic acid, and lauric acid glycerin ester, and examples of the polyglycerin fatty acid ester include mono / distearic acid diglycerin and monooleic acid decaglyceric acid. Can do.

  Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.

<Example 1>
1. Preparation of slurry for high-density support layer 150 g of ceria zirconia powder, 15 g of zirconia sol (AC-7, manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) in terms of ZrO ₂ , and a mixture containing an appropriate amount of water are prepared with a ball mill. And milled for 24 hours to obtain a slurry for a high density carrier layer.

2. Preparation of slurry for low density support layer 150 g of ceria zirconia powder, 15 g of zirconia sol (AC-7, manufactured by Daiichi Rare Chemicals Co., Ltd.) in terms of ZrO ₂ , stearic acid surfactant (Sunsoft No. 2500, A mixture containing 10 g of Taiyo Kagaku Co., Ltd. and an appropriate amount of water was prepared and stirred to obtain a slurry for a low density support layer.

3. Coating of support layer on ceramic honeycomb A ceramic honeycomb made of Nippon Choshi with a diameter of 100 mm, a length of 150 mm, and 900 cpsi (cells / square inch) was used. 50 mm from the upstream end of the ceramic honeycomb was immersed in the slurry for the high density support layer, and after taking out, excess slurry was sucked from the upstream end and fired at 350 ° C. for 30 minutes. The weight of this high density support layer was 52 g. 100 mm from the downstream end of the same ceramic honeycomb was immersed in the slurry for the low density support layer, and after taking out, excess slurry was sucked from the downstream end and fired at 350 ° C. for 30 minutes. The weight of this low density support layer was 97 g.

4). Supporting noble metal on the support layer 1.5 g and 0.4 g of Pt and Rh are supported per volume of 1 L of the ceramic honeycomb, and a mixed solution of dinitrodiammine platinum nitrate solution and rhodium nitrate solution is supported. A ceramic honeycomb having a layer was impregnated. Then, it baked at 350 degreeC for 2 hours.

<Example 2>
Example 1 except that 75 mm from the upstream end of the ceramic honeycomb was immersed in the slurry for the high density support layer and 75 mm from the downstream end was coated in the slurry for the low density support layer to coat the support layer. The weights of the high and low density support layers were 72 g and 73 g, respectively.

<Example 3>
Example 1 except that 10 mm from the upstream end of the ceramic honeycomb was immersed in the slurry for the high density support layer and 140 mm from the downstream end was coated in the slurry for the low density support layer to coat the support layer. The weights of the high and low density support layers were 12 g and 141 g, respectively.

<Comparative example>
A mixture containing 150 g of ceria zirconia powder, 15 g of zirconia sol (AC-7, manufactured by Daiichi Rare Element Chemical Co., Ltd.) and an appropriate amount of water in terms of ZrO ₂ was prepared, and this was stirred to obtain a slurry for a reference support layer. . The entire ceramic honeycomb was immersed in the slurry for the reference support layer, and after taking out, excess slurry was sucked and fired at 350 ° C. for 30 minutes. The coating amount of the reference carrier layer was 155 g. The noble metal was loaded in the same manner as in Example 1-4.

<Evaluation>
Porosity Since it is very difficult to measure the porosity of the support layer coated on the ceramic monolith substrate, the porosity of the support layer coated on the alumina sintered body having a porosity of 99% or more was measured. The porosity of the support layer was evaluated with a mercury porosimeter according to the following calculation formula. According to this formula, the porosity of the high density carrier layer, the low density carrier layer, and the reference carrier layer obtained in Examples 1 to 3 and Comparative Example was 16%, 68% and 45%, respectively.
Porosity (%) = (volume of support layer + alumina sintered body) / (apparent volume of support layer and alumina sintered body−volume of alumina sintered body)

Warmness Evaluation Warmness evaluation is performed by connecting the catalytic converters holding the ceramic honeycombs of Examples 1 to 3 and Comparative Example to a 2000 cc four-cylinder engine and operating the engine at an air-fuel ratio (A / F) of 14.5. went. The space velocity was 13,000 h- ¹ . The purification rate of HC was calculated from the ratio of the gas concentration and the gas concentration of the catalytic converter, and the time for the purification rate to reach 50% was determined. The results are shown in Table 1.

Evaluation of heat retention Using the above engine, the catalyst carrier was warmed for 10 minutes at an inlet gas temperature of 600 ° C., and the catalyst temperature was measured using a thermocouple placed 10 mm from the rear stage of the catalyst carrier. Thereafter, air was introduced from the entrance side of the catalyst carrier at a space velocity of 13,000 h ⁻¹ , the temperature of the subsequent stage 10 mm of the catalyst carrier was measured, and the time until reaching 300 ° C. was determined. The results are shown in Table 1.

  In all of Examples 1 to 3, the 50% purification time is shorter than that of the comparative example, and the warmth is excellent. In all of Examples 1 to 3, the temperature decrease time from 600 ° C. to 300 ° C. is longer than that of the comparative example, and the heat retention is excellent.

FIG. 1 is a diagram showing a catalyst carrier according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the honeycomb cell of the portion (a) having the high density support layer and the portion (b) having the low density support layer of the catalyst carrier of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Catalyst carrier 12 ... Exhaust flow upstream part 14 which has a high density support layer ... Exhaust flow downstream part 18 which has a low density support layer ... Arrow 22 which shows exhaust flow direction ... Cell wall 24 of honeycomb cell ... High density support Layer 26 ... low density carrier layer

Claims (4)

A high-density carrier layer with a porosity of 40% or less upstream of the exhaust flow;
A monolith type honeycomb catalyst carrier having a low density support layer having a porosity of 50% or more on the downstream side of the exhaust flow. The catalyst carrier according to claim 1 , wherein the low-density support layer has macropores. The catalyst carrier according to claim 1 or 2 , wherein the high-density support layer is present over 5 to 50% of the catalyst carrier length. The catalyst carrier is coated with a slurry containing a surfactant selected from the group consisting of glycerin fatty acid esters and polyglycerin fatty acid esters and a powder of the supporting layer, and the low-density supporting layer is formed by firing. The manufacturing method of the catalyst carrier in any one of Claims 1-3 containing.

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