JPH0487627A - Catalyst for reduction of diesel particulate - Google Patents

Abstract

PURPOSE:To suppress production of SO3 in a high temp. range by using a catalyst of such a structure that consists of a carrier base body the surface of which is covered with a catalyst carrier layer comprising titanium dioxide (TiO2), and platinum group metals and molybdenum deposited on the catalyst carrier layer. CONSTITUTION:The carrier base body 1 consists of a monolithic carrier base material such as ceramics or metals, foam filter, etc. On the surface of the catalyst base material 1, a catalyst carrier layer comprising titanium dioxide (TiO2) is formed. This catalyst carrier layer 2 contains coexistence of platinum group metals 3 such as Pt, Rh, Pd, etc., and Mo 4. The platinum metals 3 contribute to oxidization of SOF, HC and CO. Mo 3 is supposed to have a function to obstract oxidization of SO2 by the platinum metals 4 and to suppress production of SO3. The catalyst carrier layer 2 comprising TiO2 hardly adsorbs SO3. Thereby, high purifying efficiency for SOF, HC, CO can be maintained and the production of SO3 in a high temp. range can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst that reduces diesel particulates contained in the exhaust gas of a diesel engine (hereinafter referred to as DE).

[Prior Art] Due to strict exhaust gas regulations for gasoline engines and advances in technology that can deal with these regulations, the amount of harmful substances in the exhaust gases has been steadily decreasing. However, due to the unique situation in which harmful components are mainly emitted as particulates, regulations and technological development for DE have lagged behind those for the Kallin engine, and the development of an exhaust gas purification device that can reliably purify DE is desired. ing.

DE exhaust gas purification devices that have been developed to date can be broadly divided into methods using traps (without catalyst and with catalyst) and open-type SOF decomposition catalysts. Among these methods, the method using a trap traps particulates in the exhaust gas to control the emission, and is particularly effective for exhaust gas with a high proportion of dry suits. However, a reprocessing device is required, and the structure may crack during reprocessing.
Many practical problems remain, such as blockage due to ash and the complexity of the system.

On the other hand, open-type SOF decomposition catalysts use catalysts supporting platinum group metals, similar to those used in gasoline engines.
SOF (Solub) in particulate with C
The organic fraction is purified by oxidative decomposition. This open type SOF decomposition catalyst is
Although the dry suit has the disadvantage of a low removal rate, the amount of dry suit can be reduced by improving DE and the fuel itself, and it has the great advantage of not requiring a reprocessing device. Advances in technology are expected.

[Problems to be solved by the invention] In the open type SOF decomposition catalyst supporting platinum group metal,
SOF, HC, and Co are efficiently purified even at low temperatures, and 3
02 is discharged in a gaseous state.

However, in a high temperature range, even SO2 in the exhaust gas is oxidized and SO3 is generated, which increases the amount of particulates and reduces the purification rate (SO3 is measured as particulates, but SO2 is measured as particulates). There is a problem with this. Particularly in DE, since there is sufficient oxygen gas in the exhaust gas, the oxidation reaction of 302 is more likely to occur, and this phenomenon is remarkable. In some cases, it can more than double.

The present invention was made in view of these circumstances, and
The purpose is to suppress the formation of 503 in a high temperature range without impairing the oxidation performance for SOF, HC, and Co.

[Means for Solving the Problems] The catalyst for reducing diesel particulates of the present invention which solves the above problems comprises a carrier base material, a catalyst support layer made of TiO2 and formed on the surface of the carrier base material, and a catalyst support layer formed on the surface of the support base material. It is characterized by comprising a supported platinum group metal and Mo.

The carrier base material is similar to the carrier base material of the exhaust gas purification catalyst used in conventional gasoline engines, and monolith carrier base materials, )tm filters, honeycomb filters, pellets, etc. are used. Its material is selected from ceramic or metal.

One feature of the present invention is that a catalyst support layer made of TO2 is provided on the surface of the carrier base material.

Activated alumina is mainly used as a catalyst support layer for exhaust gas purification catalysts for gasoline engines. However, activated alumina also adsorbs S02 and easily generates 803. Therefore, in the present invention, TiO2, which does not easily adsorb SO2, is used as the catalyst support layer.

The amount of the catalyst support layer made of TiO2 is not particularly limited, and can be approximately 20 to 200Q per carrier volume 152, similar to conventional activated alumina.

The greatest feature of the present invention is that platinum group metal and MO are co-supported on the catalyst support layer made of TiOz. The platinum group metal mainly contributes to the oxidation of SOF, HC, and Co, and one or more types of Pt, Rh, Pd, etc. can be used. Especially P with high oxidation catalytic ability
It is preferable to use t.

MO is presumed to have a function of inhibiting the oxidation of 302 in platinum group metals, and suppresses the formation of 303.

There is almost no effect on SOF, HC and CO to inhibit the oxidation reaction.

The amount of platinum group metal supported is preferably 0.05 to 2 g per 1Q of carrier volume. S if less than 0.05g
It has inferior oxidizing performance to OF, and even if more than 2 g is supported, the effect will be saturated and the cost will increase. In addition, the amount of MO supported is 0.05 to Q as metal per carrier volume 19,
5 mol is preferred. S if less than 0.05 mol
O3 is easily generated, and the effect is saturated even if more than 5 mol of Q is supported.

[Operation of the invention] The catalyst for reducing diesel particulates of the present invention has the following features:
The catalyst support layer made of TiO2 hardly adsorbs SO2.

It is generally assumed that MO interferes with the oxidation catalytic action of SO2 by the platinum group metal, and the synergistic effect of the two reliably prevents the oxidation of SO2.

In addition, since Mo has almost no effect of inhibiting the oxidation catalytic action of platinum group metals such as SOF,
and CO are purified in the same manner as before by the oxidation catalytic action of platinum group metals.

[Effect] Therefore, according to the catalyst for reducing diesel particulates of the present invention, a high purification rate of SOF, HC, and CO is maintained from a low temperature range to a high temperature range, and oxidation of 802 is prevented in a high temperature range. , 303 is prevented, and diesel particulates can be reliably reduced.

[Example code] Hereinafter, this will be explained in detail using examples.

(Example 1) FIG. 1 shows an enlarged cross-sectional view of the main parts of the catalyst for reducing diesel particulates of this example. This catalyst is composed of a cordierite monolith carrier base material 1, a catalyst support layer 2 made of TiO2 formed on the surface of the carrier base material 1, and Pt3 and MO4 supported on the catalyst support layer 2.

The catalyst supporting layer 2 was formed in an amount of 75 g per carrier base material 152. In addition, Pt3 is 1Ω per 1Q of carrier base material, M o
4 Lt carrier base material 151! 0.01m per.

It is carried.

The method for producing this catalyst will be explained below.

A cordierite monolith carrier base material 1 having a volume of 1.7Q was prepared, and a TiO2 layer was formed on the surface of the carrier base material using a slurry consisting of TiO2 powder, titania sol, and distilled water. After drying at 120℃ for 2 hours, drying at 700℃ for 2 hours.
The catalyst support layer 2 was formed by baking for a period of time. Note that the catalyst supporting layer 2 is a carrier base material 15! It was 75g per serving.

Next, the carrier base material 1 having the catalyst supporting layer 2 was immersed in a dinitrodiamine platinum solution of 1 Q/Q for 1 hour, pulled up, blown off excess moisture, dried at 120° C. for 2 hours, and then 5
Calcinate at 50°C for 1 hour to obtain 1q of P per 1Q of carrier base material.
It carried l. Roughly immersed in a 0.007 mo 1152 ammonium molybdate solution for 1 hour, pulled out, blown off excess moisture, dried at 120°C for 2 hours, and then
0.01 per 152 carrier base materials after baking at 0°C for 2 hours
MO of m01 was supported.

(Example 2) The catalyst for reducing diesel particulates of this example was:
The structure is the same as that of Example 1 except that the amount of MO supported is different. That is, using 0.035 m01152 ammonium molybdate solution, 0
．． 05m0 I of Mo was supported.

(Example 3) The diesel particulate reduction catalyst of this example also
The structure is the same as that of Example 1 except that the amount of Mo supported is different. That is, 0.07m.

1152 ammonium molybdate solution was used to support 0.1 mo+ MO per carrier substrate 19.

(Example 4) The diesel particulate reduction catalyst of this example also
The structure is the same as that of Example 1 except that the amount of MO supported is different. That is, 0.35m.

Using a +152 ammonium molybdate solution, 0.5 mo+ of MO was supported per 1Q of carrier base material.

(Example 5) The diesel particulate reduction catalyst of this example also
The structure is the same as that of Example 1 except that the amount of Mo supported is different. That is, using an ammonium molybdate solution of 0.49 m0/Q, 0.7 m per carrier base material 19
01 Mo was supported.

(Comparative Example 1) The catalyst of Comparative Example 1 consisted of the same carrier base material as in Example 1, a catalyst support layer made of γ~alumina formed on the surface of the carrier base material, and Pt supported on the catalyst support layer. It consists of The catalyst supporting layer was formed in an amount of 75 g per carrier base material. Moreover, Pi is the carrier base material 1f! It is carried for 1Q.

This catalyst is applied as a slurry into which the carrier substrate is immersed.
It was formed in the same manner as in Example 1, except that a slurry consisting of alumina, alumina sol, and distilled water was used, and no MO was supported.

(Comparative Example 2) This catalyst has the same structure as Example 1 except that MO is not supported. It was formed in the same manner as in Example 1 except that the MO supporting step of Example 1 was not performed.

(Test) The catalysts of Examples 1 to 5 and Comparative Examples 1 and 2 were each attached to the exhaust system of an overflow chamber type DE having a displacement of 2000 cc, and the HC purification rate was measured. The results are shown in Table 1. In addition, using a non-dispersive infrared analyzer, S
Measure the O2 concentration and the SO2 concentration in the outgas, and use the following formula to calculate 3.
The addition rate of 03 was determined. The results are shown in Table 2.

Conversion rate = (Incoming gas SO2 concentration - Outgoing gas SO2gL degrees)
100/concentration of incoming gas 302 Note that the measurement conditions are the following four conditions.

(1) 2000rpm x 6kgfm, gas input 3
00℃ (2> 2000rpm x 8kpfm, gas input 350℃ (3) 2000rpm xl 0kof
m, gas input 400℃ (4) 2000rpm xl 2
kgfm, input gas 450°C (evaluation) From Table 1, the catalyst of Comparative Example 1 has a particularly good HC purification rate, but the catalysts of each Example are equivalent to the catalyst of Comparative Example 2 in each temperature range. The purification rate within the practical range is shown in Table 1, Table 2. Further, no significant difference was observed depending on the amount of MO supported, and it is clear that MO does not inhibit the oxidation catalytic action of Pt.

Furthermore, Table 2 shows that in the catalysts of Examples, as the amount of MO supported increases, the temperature at which SO3 is not produced shifts to a high temperature range. That is, the more MO supported, the less 303 is produced even at high temperatures, but this effect is saturated when MO exceeds Q,5mo1.

On the other hand, in the catalysts of Comparative Example 1 and Comparative Example 2, 303 was generated even at 300°C, but the difference with the catalyst of Example was that M
It is clear that this is caused by the presence or absence of O support, and M
It is presumed that o interferes with the oxidation of SO2. Further, when comparing Comparative Example 1 and Comparative Example 2, the catalyst of Comparative Example 2 has a lower overall conversion rate of 303. It is clear that this is due to the difference in the material of the catalyst support layer, and it is confirmed that TlO2 is difficult to adsorb SO2.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view of the main parts of the catalyst for reducing diesel particulates of the present invention. 1...Carrier base material 2...Catalyst supporting layer 3...
・Pt 4-M0 Patent Applicant Toyota Motor Corporation Cataler Industries Co., Ltd. Agent Patent Attorney Hiroshi Okawa

Claims (1)

[Claims] (1) A diesel patty comprising a carrier base material, a catalyst support layer made of titanium dioxide and formed on the surface of the carrier base material, and a platinum group metal and molybdenum supported on the catalyst support layer. Catalyst for curation reduction.