JPH02149308A - Filter for collecting and purifying fine particle - Google Patents

Abstract

PURPOSE:To enhance ignitibility at low temp. and the initial performance of a catalyst by blending molybdenum oxide with a platinum group catalyst and carrying this blended substance as a filter for collecting and purifying fine particles. CONSTITUTION:In a fine particle collecting and purifying filter for collecting and purifying particulate grains contained in exhaust gas discharged from a diesel engine, etc., molybdenum oxide is blended with one or more kinds of metal selected from among palladium, rhodium and platinum and the blended substance is carried on the surface of a filter base body made of ceramic. Molybdenum oxide is easily diffused in the collected particulate grains and thereby the particulate grains are made easy to be burned at low temp. The initial performance and ignitibility of the filter are enhanced. Therefore regenerative properties of this filter is enhanced and utilization in a long period is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a particulate collection and purification filter that collects particulates 1 to 1 contained in the exhaust gas of a diesel engine, etc., and purifies the exhaust gas. More specifically, it relates to a particulate collection and purification filter in which the particulates are burned off by ignition for reuse.

[Prior Art 1] Exhaust gas from an internal combustion engine such as a diesel engine contains fine particles (vatigules) mainly composed of carbon. A ceramic honeycomb structure (honeycomb filter), a foam filter having a three-dimensional mesh structure, and the like are known as particulate collection and purification filters that collect and convert these particulates into 6-carbon particles. In these filters, as the mileage of the vehicle increases, particulates accumulate in the exhaust passage, and pressure loss gradually increases due to erosion, leading to a decrease in engine output.

However, since most of these particulates are carbon particles, they can be burned and removed by heating. Through this operation, the particle collection and purification filter can be regenerated. As a method for regenerating this particulate collecting and purifying filter, a method has been developed in which the collected particulates are burned off using an external ignition means such as a burner or an electric heater. In order to ensure the combustion of the particulates, it is effective to support a catalyst on the filter base of the particulate collection and purification filter.

Catalysts that facilitate the regeneration of this diesel particulate are palladium catalysts and rhodium catalysts disclosed in JP-A No. 55-24597, as well as improved catalysts such as those disclosed in JP-A-61-129030. discloses a catalyst consisting of palladium or rhodium and one of copper, zinc, manganese, and lanthanum.

Further, Japanese Utility Model Application Publication No. 62-98718 discloses that the ignition and combustibility is improved by plating the filter base with copper and silver.

[Problems to be Solved by the Invention] The catalyst supported on the particulate collection and purification filter must have excellent initial performance and durability. The initial performance I'm talking about here is J3's performance on a new filter.
Re-1 can be removed by combustion at low temperatures. Furthermore, durability refers to having a stable catalytic action over a long period of time with small fluctuations in ignition temperature due to thermal history over time.

Although platinum group catalysts such as the palladium catalyst and rhodium catalyst described above have excellent durability, their initial performance is insufficient. Catalysts made of palladium or rhodium and one of copper, zinc, manganese, and lanthanum have excellent durability, but are still insufficient in initial performance, particularly in ignition performance. On the other hand, those plated with copper and silver have poor initial performance.
Although it has excellent ignitability, heat tends to oxidize or sulfide the copper, resulting in poor durability.

[1] An object of the present invention is to further improve the performance of a particulate collection and purification filter by using the above-mentioned catalyst having good initial performance, ignitability, and durability.

[i! Means for Solving Problem II] The present invention was completed based on the discovery that ignitability at low temperatures can be improved by incorporating and supporting molybdenum oxide in a platinum group catalyst.

The particulate collecting and purifying filter of the present invention includes a ceramic filter base, a catalyst supported on the surface of the filter base, and a particulate filter that collects particulates contained in engine exhaust gas. The catalyst is characterized in that it is composed of a small amount of a metal selected from palladium, rhodium, and platinum, and an oxide of molybdenum.

This particulate collection purification filter is directly attached to the filter base.
Alternatively, the catalyst is supported on a porous ceramic support layer provided on the surface of the filter base.

The ceramic filter base can be made of ceramics such as cordierite, mullite, and spinel. The shape of the filter base body may be a honeycomb shape or a foam shape having a three-dimensional network structure, and any shape can be used, but the shape is not limited to these.

Preferably, a porous ceramic support layer is formed on the surface of the filter base. The purpose of this ceramic support layer is to improve the particulate collection performance or to prevent the collected particulates from re-dispersing, and is selected from alumina, titania, magnesia, silica, etc. Preferably, it is made from Y-alumina.

The catalyst supported directly on the filter base or on the ceramic support layer is composed of at least one metal selected from palladium, rhodium, and platinum and an oxide of molybdenum. However, by supporting at least one selected from palladium, rhodium, and platinum, which are platinum group elements with excellent oxidation performance, and an oxide of molybdenum, the initial performance and durability of the catalyst can be improved.

In addition, palladium, a platinum group element, is 0 per apparent body 1111.Il of the filter.
．． 5 to 5.0 g is desirable. This is because the best performance is achieved when the catalyst properties are within the above range. .

The amount of molybdenum oxide supported is preferably 0.05 to 0.5 mol per apparent volume IJl of the filter. 0.0
If the amount is less than 5 moles, the effect of adding molybdenum will not appear, and 0
．． If the amount exceeds 5 mol, the catalytic effect commensurate with the increase in the amount added cannot be obtained even if more than this amount is supported.

Next, a typical manufacturing method of the particulate collection and purification filter of the present invention will be described. First, as with the conventional honeycomb filter, )A
- Forming a filter base such as a membrane filter. At this time,
Preferably, a supporting layer of porous ceramics is formed on the surface of the Noirta substrate. The filter base is then immersed in a solution containing platinum group element ions, dried and fired, and then the filter base is immersed in a solution containing rifden ions and dried to support the catalyst on the surface of the filter base. By changing the concentration of the dipping solution, the amount of catalyst supported can be changed.

[Function] The particulate collection and purification filter of the present invention supports at least one metal selected from palladium, rhodium, and platinum and an oxide of molybdenum as a catalyst. The platinum group element catalyst increases the durability of the particulate collection and purification filter. Molybdenum oxide can improve the initial performance and ignitability of the catalyst. This molybdenum oxide tends to diffuse into the collected particulates, thereby preventing the particulates from burning at low temperatures.
It is thought that the initial performance and ignitability of the filter are improved. Therefore, this particle collection and purification filter has improved reproducibility and can be used for a long period of time.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

(Example 1) A cordierite honeycomb structure having a large number of passages parallel to the axial direction was used as a filter base. This filter base has passages open at both ends and has a diameter of 30 m.
m, and the length is 5Qmm.

First, 100 parts by weight of Y-alumina powder, 1 part by weight of alumino-sol
60 parts by weight of the filter substrate, 60 parts by weight of aluminum nitrate, and 50 parts by weight of water.
After soaking for 12 seconds, pulling out and blowing off excess droplets,
It was dried at 0° C. for 3 hours and then fired at 700° C. for 2 hours to form a porous ceramic support layer made of Y-alumina on the walls forming the passages of the filter base.

Next, using an aqueous solution containing palladium chloride, the filter base with the support layer formed thereon is immersed in this aqueous solution for 1 hour to adsorb palladium, and then an aqueous solution of sodium to lithium boron hydride is added to the support layer of the filter base material. After being immersed in water for reduction treatment, it was washed with water, dried, and then fired at 500°C for 0.5 hours.

Next, the filter substrate carrying palladium was added to an aqueous ammonium molybdate solution having a concentration of
After soaking for a minute, the filter base was pulled up and excess droplets were blown off, dried at 120°C for 3 hours, and then baked at 300°C for 2 hours to obtain Filter A. As a result of the above operations, 1 g of palladium and 0.1 mole of molybdenum oxide were supported on the filter Δ per 1 blade of the apparent volume of the filter base.

Another filter substrate carrying palladium in the same manner as above was immersed in an ammonium molybdate aqueous solution having a concentration of 0.007 mol/ρ, and the same treatment as for filter Δ was performed to obtain Filter B. This filter B carried 19 moles of palladium and 0.01 mole of molybdenum oxide per 1Q of the apparent volume of the filter base.

Another filter substrate carrying palladium in the same manner as above was immersed in an ammonium molybdate aqueous solution with a concentration of 0.035 mol/liter, and the same treatment as for filter △ was performed to obtain filter C with a weight of 1q. . This Filter C carried 19 moles of palladium and 0.05 moles of molybdenum oxide per gram of the apparent volume of the filter base.

Another filter substrate carrying palladium in the same manner as above was immersed in an aqueous ammonium molybdate solution with a concentration of 0.35 mol/. . This filter D has an apparent volume of 1. 19 palladium and 0.5 mol of molybdenum oxide were supported per liter.

Another filter substrate carrying palladium in the same manner as above was immersed in an ammonium molybdate aqueous solution having a concentration of 0.49 mol/ρ, and the same treatment as Filter A was performed to obtain Filter E. This filter E has
1 g of palladium and 0.7 mol of [libdenum oxide] were supported per 11 apparent volumes of the filter substrate.

(Example 2) An alumina support layer was formed on the same filter substrate as in Example 1 by the same method. This filter base was immersed in a 1 g/ρ aqueous solution of diodium IX chloride for 1 hour, then immersed in an aqueous solution of notrium borohydride for reduction, and fired (500'
cX0.5H) to support 1 q of rhodium per 11 apparent volumes of the filter substrate. Furthermore, this filter base was heated to 0.07 t/f in the same manner as in Example 1.
The filter substrate was immersed in an ammonium molybdate aqueous solution having a concentration of 0.1 mol per gram of apparent volume of the filter substrate to support it.

(Example 3) An alumina support layer was formed on the same filter substrate as in Example 1 by the same method. This filter base was immersed in a 1a/p platinum chloride aqueous solution for 1 hour, reduced, and fired to support 1 g of platinum per 1 g of the apparent volume of the filter. Next, this filter base was immersed in a 0.07 mol/1 ammonium molybdate aqueous solution in the same manner as in Example 1 to oxidize 0.1 mol of molybdenum per 1 mol/l concentration of the filter base. carried things.

(Comparative Example 1) An alumina support layer was formed on the same filter base as in Example 1. This filter base was immersed in an aqueous palladium chloride solution of 19/ρ for 1 hour, reduced with an aqueous sodium borohydride solution, and washed with water. It was immersed in a rhodium chloride aqueous solution of Oa/41 for 1 hour, pulled up, washed with water, and dried and fired (500'CX0.5H). Through this operation, 1 g of each of palladium and rhodium was supported per apparent volume of the filter substrate.

(Comparative Example 2) An alumina support layer was formed on the same filter base as in Example 1. This filter base was immersed in a 1g/I) palladium chloride aqueous solution for 3 minutes, then pulled up and reduced with a hydrogenated sodium chloride aqueous solution to form electroless plating nuclei on the alumina support layer on the filter base. Electroless copper plating was performed by immersing it in a copper plating solution. At this time,
The amount of copper plating was 20q per 1.0 volume of apparent G of the filter. Next, a solution consisting of 7.5 Q/fJ of silver nitrate, 6.4 ml/ρ of aqueous ammonia (28% 'a degree), and 26 CJ/Jl of sodium thiosulfate was prepared, and the support layer of the copper-plated filter base was immersed in it. Then silver substitution plating was performed. With this operation, the apparent volume of the filter is 1. A filter was obtained in which 20 g of copper was deposited per liter and 2 q of silver was deposited on the top surface.

(Comparative Example 3) An alumina support layer was formed on the same filter base as in Example 1. This filter base was immersed in a palladium chloride aqueous solution of 1Q/ρ for 1 hour to remove
After reducing with aqueous solution of aluminum and washing with water, drying and firing (50%
0° C. x 0.5+1) to support 1 q of palladium per 1.0 filter.

Next, this filter was immersed in an aqueous solution of 0.07 tL/fJ of Si to adjust its content, pulled up, blown away excess droplets, dried, and baked at 600° C. for 2 hours. Through this operation, a filter F was prepared in which 0.1 mol of copper oxide was supported per 1 apparent volume of the filter base.

Similarly, a filter carrying palladium was immersed in an aqueous solution of manganese nitrate at 0.07 mol/ρ to produce a filter G carrying 0.1 mol of manganese oxide.

Furthermore, in place of manganese in filter G, 0.07 t/f
The apparent volume of the filter substrate was immersed in an aqueous ammonium metavanadate solution of 1. A filter H was prepared in which 0.1 mol of vanadium oxide was supported per Il.

(Evaluation) Each of the filters produced in the above Examples and Comparative Examples was attached to the exhaust system of an overflow chamber type diesel engine with an exhaust of 2400 cc, and the rotation speed was 200 Orpm and the torque was 3 k.
The filter was operated for 2.5 hours under the conditions of 0.6 to 0.65 g of particulates per filter.

Next, this filter is assembled into the test equipment shown in Figure 1.

This test device consists of a cylindrical reaction tube 1 having a gas inlet 6 and a gas outlet (8) on both end faces, and a joint surface 9 on which a filter can be inserted and removed, and a reaction tube on the side of the gas inlet 6. 1
An electric furnace 2 is disposed so as to cover the outer periphery of the furnace. Inside the reaction tube 1, a monolith carrier 4 for gas rectification, a heater 7, and a filter 5 are arranged in this order from the gas inlet 6 side. Then, a mixed gas of nitrogen and oxygen is introduced through the gas inlet 6 and heated in the electric furnace 2, and then the mixed gas flow is rectified by the monolith carrier 4 for rectification, and the end face side of the filter is heated by the heater 7. It has been introduced in 7. Emission [18
The structure is such that exhaust gas from burning particulates 1- and unreacted gas are discharged through a filter 7. The heater 7 heats one end surface of the filter 5 by applying electricity, and is provided with a thermometer and a relay (not shown) to adjust the temperature of the end surface of the filter 5 and maintain it at a predetermined temperature. First, nitrogen gas 4.5jl/min, oxygen gas 0.5. Q/m
A mixed gas was introduced into the reaction tube at a flow rate of 1.5 in, and the amount of electricity applied to the heater 2 was adjusted to change the temperature of the end face of the filter 5 to three levels (at 25°C intervals) as shown in Table 1 to avoid particulates. The relationship between the combustion rate and the heating temperature was measured.The particulate combustion rate was determined by setting the weight of particulates before measurement as Wl, and the weight of particulates after measurement as W2. (Wl-W2 > /WI
Calculated by the formula of x100.

First, after measuring the particulate combustion rate when new, heat treatment was performed at 800°C in an electric furnace.

Next, the particulate combustion rate was measured using the same procedure as when using a new product. After further heat treatment at 1000°C for 3 hours, the combustion rate was measured in the same manner as in the case of 800°C. The results are shown in Tables 1 and 2.

When the catalyst of Comparative Example 1 was made of only palladium and rhodium, the initial performance was poor. When the copper-silver plating of Comparative Example 2 was applied to the support layer, the new product ignited at a low temperature and had excellent initial performance, but heat treatment lowered the ignition temperature of the particulates (
(This refers to the initial temperature at which the combustion rate is entered in Table 1.2) increases, and the catalyst deteriorates significantly, resulting in poor durability. Comparative Example 3, a conventional example in which copper, manganese, and vanadium were added to the platinum group catalyst, had excellent durability, but showed insufficient initial performance and low-temperature ignitability.

On the other hand, A of Example 1 of the present invention shows better initial performance and better ignitability even after heat treatment than Comparative Example 1, that is, the temperature at which the combustion rate is high is lower than that of Comparative Example. Also, compared to Comparative Example 2,
Although it is slightly inferior when new and after heat treatment at 800℃ for 3 hours, the increase in ignition temperature is small even after heat treatment.1
The ignition temperature is 75℃ compared to after heat treatment at 000℃ for 3 hours.
is also low and good.

The platinum group elements were changed from palladium in Example 1 to Example 2.
When platinum in Example 3 was used instead of rhodium in Example 3, the same effect as in Example 1 was obtained. In other words, the ignition temperature is the same and is superior to the conventional example.

B-E of Example 1 was obtained by changing the amount of supported molybdenum oxide. From the result of B, when the amount of supported molybdenum oxide is 1/10 of that of A, the effect of adding molybdenum is small. Hereinafter, C is 1/2 the amount, D is 5 times the amount of A, and E
The amount of supported molybdenum oxide was changed to 7 times that of △. C was slightly inferior in ignitability after heat treatment compared to A. D and E showed the same performance as No. 8, and had slightly better ignitability than No. 8. This shows that the effect of molybdic acid is small when the amount of material supported is small, and that the performance does not improve even if more than a certain amount is added, and the amount of supported molybdenum oxide is It is preferably 0.05 to 5.0 mol per 1 ρ volume of the filter's apparent Gp.

[Effects] By supporting platinum group elements and molybdenum oxides as catalysts, the particulate collection and purification filter of the present invention has improved initial performance compared to conventional platinum group catalysts, and has low deterioration due to heat and is durable. This improves the performance and enables effective filter regeneration.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a test device used to evaluate the regeneration performance of the catalyst.

Claims (1)

[Claims] (1) A particulate collection and purification filter that consists of a ceramic filter base and a catalyst supported on the surface of the filter base and that collects particulates contained in engine exhaust gas, the catalyst comprising palladium, palladium, A particulate collection and purification filter comprising at least one metal selected from rhodium and platinum and an oxide of molybdenum.