JPH0629542B2 - Diesel particulate collection filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a filter for collecting diesel particulates.

[Conventional technology]

In order to prevent the filter function from being deteriorated by blocking the particulates mainly composed of carbon fine particles in the filter for collecting diesel particulates, the filter is loaded with various catalysts to burn the particulates at a lower temperature, It is known to improve the reproducibility of filters. Various catalysts such as platinum group metals and base metals have been proposed as catalysts for improving the reproducibility of this filter. Platinum (Pt) is a platinum group metal, and copper (Cu) is a base metal, which has a relatively good reproducibility. It is said to have.

Also, although the main purpose is not for particulate combustion,
Cr ₃ CuNi _1.4 O ₁₀ found in Japanese Patent Publication No. 54-38598 and Co ₁ found in Japanese Patent Publication No. 56-52619 as complex oxide catalysts.
~ ₆ Mn ₁ ~ ₂ CuO ₁₀ etc. have also been proposed. Further, as a filter regenerating means, a method using an external ignition means such as a heater or a burner or a method of raising the exhaust gas temperature to a temperature higher than the combustion temperature of particulates by means of suction / exhaust throttling or the like is adopted.

[Problems to be solved by the invention]

However, none of the above catalysts has yet achieved satisfactory effects in terms of ignitability and particulate combustibility. Further, the filter material is exposed to a high temperature of about 1000 ° C. or higher due to the combustion heat of particulates during regeneration, but there is a problem that any of the above catalysts is significantly deteriorated under such a high temperature condition.

[Means for solving problems]

In order to solve the above problems, the present invention provides the general formula A
_{1-x A'x} B _{1-y B'y} O ₃ (wherein A is one or more elements selected from rare earth elements, A'is one or more elements selected from alkaline earth elements, B, B'is Cr, Mn, F
e, Co, Ni, Cu, 0 ≦ x ≦ 1, 0 ≦ y
≦ 1. The present invention provides a filter for collecting diesel particulates, characterized in that the carrier having a filter function is coated with a perovskite type complex oxide represented by the formula (1).

The carrier having a filter function may be any carrier of a conventional particulate collection filter, for example,
In addition to a honeycomb structure or a porous structure of cordierite, alumina, mullite, aluminum titanate, etc., in a filter simply packed with particles, the particles are also carriers.

Formula _{A 1-x} A _{'perovskite-type} composite oxide represented by x B _1-y B'O ₃ is, A, A', B, a solution containing B 'in a desired composition, usually an acidic solution, typically Can be obtained by adding an alkali to a nitric acid solution to coprecipitate the hydroxides of A, A ', B and B', drying and firing.

Supporting the composite oxide on the carrier is performed by immersing the carrier in a slurry in which the composite oxide is dispersed, impregnating the carrier, and then drying,
It can be fired as necessary. Also, A,
Immersing the carrier in a dispersion or solution containing A ', B, B',
It is also possible to impregnate them, dry them, and then calcinate them to support the perovskite-type composite oxide.

The amount of the complex oxide supported on the filter carrier is 25 to 150.
g (per filter volume), preferably 75 to 125 g
The degree is good.

Further, it is preferable to disperse and support a platinum group metal, particularly platinum, in the composite oxide because the ignition temperature and the peak temperature are lowered. The platinum group metal may be supported by impregnating the composite oxide on the filter carrier, then impregnating the composite oxide, then drying and firing, or by impregnating the composite oxide, drying and firing, and then supporting it on the filter together with the complex oxide. .

[Action]

The particulate trapping filter carrying the complex oxide represented by the above general formula has improved reproducibility (ignition temperature, peak temperature), and its high temperature durability due to being an oxide. It is considered that the improvement in the reproducibility is due to the high oxidative activity of this composite oxide.

〔Example〕

Example 1 In order to synthesize a composite oxide represented by A _1-x A ′ _x B _1-y B ′ _y O ₃ , an A element was La, an A ′ element was Sr,
Co, Mn, Fe, Cr, Ni, C as B and B'elements
A nitrate solution of u was prepared, and a mixed aqueous solution having a concentration adjusted so as to have a desired composition shown in Table 1 was prepared. Next, an aqueous NaCO ₃ solution was gradually added dropwise to this mixed solution with stirring to coprecipitate these elements as hydroxides. The obtained precipitate was thoroughly washed with water, filtered off, dried, pulverized and calcined in the air at 800 ° C. to obtain a perovskite type complex oxide powder having the composition shown in Table 1.

The product was identified by X-ray diffraction, and it was confirmed that a perovskite type complex oxide was formed in each product.

Example 2 The powder having the composition of La _0.8 Sr _0.2 CoO ₃ obtained in Example 1 was impregnated with a PdCl ₂ solution, dried and baked at 600 ° C. in the atmosphere for 3 hours to obtain Pd / La containing 0.15 wt% of Pd. _0.8 Sr _0.2 CoO ₃ powder was obtained. Also, in the same operation, using H ₂ Ptcl ₆ solution, Pt / L
A _0.8 Sr _0.2 CoO ₃ powder was also obtained.

Comparative Example 1 An activated alumina powder having an average particle size of about 10 μm was impregnated with a Cu (NO ₃ ) ₂ aqueous solution, dried and fired to prepare an activated alumina powder containing 5 wt% of Cu.

Comparative Example 2 An activated alumina powder having an average particle size of about 10 μm was impregnated with an aqueous Pdcl ₂ solution, dried and fired to prepare an activated alumina powder containing 0.25 wt% of Pd.

Test Example 1 The perovskite type complex oxide powder prepared in Examples 1 and 2 (see Table 1 for details) and the catalyst powder prepared in Comparative Examples 1 and 2 were mixed with a commercially available carbon black powder, and the mixture was analyzed by a thermal analyzer. The ignition temperature of carbon black was measured. At this time, the amount of carbon black mixed was 10 wt% and the temperature increase rate of the thermal analysis device was 10 ° C / min. The sample with the highest performance was subjected to heat treatment (1000 ° C, 10 hours) for ignition after endurance. The temperature was also measured. The results are shown in Table 1.

From Table 1, it can be seen that the perovskite type complex oxide according to the present invention can remarkably lower the combustion temperature of the carbon fine particles which are the main component of the particulates in the diesel exhaust, and Co at the B and B'positions. , Cu, Mn, F
It can be seen that even if any transition metal such as e, Cr, or Ni is provided, it has better performance than the conventional CuO or PdO catalyst. Although some examples of changing the ratio of A and A'are also introduced, they have better performance than conventional catalysts,
It can be seen that the performance can be further improved by coexisting a platinum group catalyst, particularly Pd, with the present perovskite oxide. It can be said that this perovskite type oxide is also excellent in durability since the flammability of the carbon black hardly deteriorates even if it is heat-treated at 1000 ° C.

In Example 1 of Table 1, La _0.8 Sr _0.2 CrO ₃ and La
NiO ₃ has the same ignition temperature and peak temperature as those of Comparative Example 1. However, Pd of Comparative Example 1 in Table 1
O and CuO have a low firing temperature of 600 ° C at the time of preparation, and show performance in a state where they are not substantially deteriorated. PdO and C
When uO receives heat of about 1000 ° C, its ignition performance deteriorates rapidly. On the other hand, La _0.8 Sr _0.2 CrO ₃ and LaNiO ₃ are stable at high temperatures and are superior to conventional catalysts PdO and CuO in terms of high temperature durability.

Test Example 2 The following experiment was conducted in order to confirm the effect of the present invention in a form closer to that of an actual machine. The specific operation is as follows.

(1) La _0.8 Sr _0.2 CoO ₃ powder showing good performance was dispersed in 1 ml of ethyl alcohol at a ratio of 1 g to form a slurry.

(2) A commercially available cordierite honeycomb filter (diameter 30 mm, length 50 mm, porosity 60) was added to the prepared slurry.
%) And the slurry was attached to the filter material.

(3) Take out this filter from the slurry, blow off excess slurry with compressed air, and then repeat drying several times, and bake at 800 ° C x 3h to make La _0.8 Sr _0.2 CoO ₃ about 100g per filter volume. A coated filter A was obtained.

(4) A commercially available cordierite honeycomb filter (the same as that described above) was prepared, and an active alumina coat layer was formed on the filter using a slurry composed of activated alumina powder, aluminum nitrate, alumina sol, and distilled water. The coating amount is about 75 g per filter volume.

(5) Next, the filter was immersed in a PdCl ₂ solution, dried and fired to obtain a filter B carrying 1 g of Pd per 1 of the filter melt.

(6) Install the obtained filters A and B in the exhaust system of a 2.4 vortex nitrogen diesel engine, 2,000 rpm torque 3 kg
・ Operating for 2 hours at m, 0.6 to 0.6 per filter
5 g of particulates were collected.

(7) This filter was attached to the evaluation device shown in FIG. 1, and the gas temperature (N ₂ —O ₂ gas, O ₂ 10 vol%, flow rate;
10 / min) was increased at 30 ° C./min to measure the ignition temperature. In FIG. 1, 1 is a reaction tube, 2 is an exhaust tube, 3 is a N ₂ —O ₂ gas introduction tube, 4 is a filter, 5 is a rectifier,
6 is an electric furnace. The ignition temperature was determined using the rise curve of the temperature inside the filter, and after the filter regeneration operation, the burning rate of particulates was also calculated by the gravimetric method. The results are shown in Table 2.

Table 2 shows that the perovskite-type composite oxide according to the present invention can burn particulates at a lower temperature than conventional catalysts even when coated on an actual filter material. In the examples and test examples, A,
La and Sr have been introduced as representatives of A ', respectively. The combustion characteristics of such particulates are due to the oxygen deficiency generated between the A and A'elements and the oxidation activity obtained by the transition metal arranged in B and B'. And therefore A
The same effect can be obtained by using Ce, Pr, Nd, Y or other rare earth element as the element to be arranged in the above, and Ba, Mg, Ca or other alkaline earth element as the element in the arrangement to A '.

〔The invention's effect〕

The particulate collection filter carrying the specific perovskite-type composite oxide of the present invention has improved filter reproducibility (combustion temperature of particulates, etc.) and is more durable than conventional products. There is.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for evaluating characteristics of a filter according to an embodiment. 1 ...... reaction tube, 2 ...... exhaust pipe, 3 ...... _N 2 -O ₂ gas inlet, 4 ...... filter, 5 ...... rectifier, 6 ...... electric furnace.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Kimura Ai Prefecture Nagakute Town, Aichi Prefecture, Oita, Nagakage 1 No. 41 Yokomichi Toyota Central Research Institute Co., Ltd. (72) Inventor Masa Suzuki, Aichi Prefecture Nagakute Town, Aichi Prefecture 1 in 41, Yokomichi, Nagatoji (56) References JP-A-58-43214 (JP, A) JP-A-61-129030 (JP, A) JP-A-61-146314 (JP, JP-A) A) JP-A-63-65927 (JP, A)

Claims (2)

[Claims] 1. A general formula A _1-x A ′ _x B _1-y B ′ _y O ₃ (wherein A is one or more elements selected from rare earth elements, A ′
Is one or more elements selected from alkaline earth elements, B,
B ′ is selected from Cr, Mn, Fe, Co, Ni and Cu, and 0 ≦ x ≦ 1, 0 ≦ y ≦ 1. ) A diesel particulate filter for collecting diesel particulates, characterized by comprising a carrier having a filter function coated with a perovskite type complex oxide represented by the formula (1). 2. The filter according to claim 1, wherein a platinum group metal is dispersed and carried in the composite oxide.