JPS634850A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance purification capacity as low activity at low temp. and also to maintain the purification capacity at high temp. by regulating the amount to be deposited of composite oxide of rare earth elements having a perovskite structure to the specified proportion of a catalyst body. CONSTITUTION:In a catalyst for purifying incomplete combustion gas such as exhaust gas discharged from automobiles and factories, etc., after firstly mixing alumina cement and melted silica at half and half and sufficiently kneading the mixture with a binder and water, it is pressurized and molded into a honeycomb shape, dried and sintered to obtain a carrier. Thereafter the material mixed with both composite oxide of rare earth elements having a perovskite structure and same material as the carrier is coated on this carrier, dried and sintered. In this case, the amount of perovskite to be deposited is regulated to about 1-5wt% of the catalyst body. By such a way, the purification capacity for NO2 is enhanced as low activity at low temp. and both the purification capacity for NO2 at high temp. and the purification capacity for CO at low temp. are made to high degree of purification.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a catalyst body for purifying incompletely combusted gases such as exhaust gases discharged from automobiles, factories, etc., and combustion exhaust gases such as oil and gas.

Conventional technology Conventionally, this type of porous catalyst for exhaust gas purification has an excellent purification ability for carbon monoxide and hydrocarbons because it is an oxidation catalyst, but it has a considerably negative purification ability for nitrogen dioxide at low temperatures. (ability to reduce No2 to No). In other words, at low temperatures, rather than purifying nitrogen dioxide, it actually increases.

Problems to be Solved by the Invention As described above, conventional catalysts having a perovskite structure have had problems in their ability to purify nitrogen dioxide at low temperatures.

The present invention solves the above-mentioned conventional problems, and improves the amount of perovskite catalyst supported in order to improve the purifying ability of the catalyst.

Means for Solving the Problems In order to achieve this object, the present invention is such that the amount of perovskite catalyst supported is 1 to 5 wt% of the catalyst body,
More preferably, the perovskite catalyst and the carrier are mixed with water, and the mixture is applied to the carrier, dried, and fired.

By this means, the negative purification ability of the perovskite catalyst for nitrogen dioxide purification at low temperatures can be improved by decreasing the activity, and - carbon oxide purification ability, hydrocarbon purification ability, and nitrogen dioxide purification ability at high temperatures can be improved. A high value of purification ability can be obtained.

Example Examples will be described below.

First, the carrier was prepared by adding an appropriate amount of binder and water to powder of a mixture of about 50 wt% each of alumina cement made of Al2O3, CaO, and 5102 and fused silica, kneading well, and then pressure-molding it into a honeycomb shape and drying it. The binder was then removed at a temperature of about 60''C and finally sintered at a firing temperature of 1,000°C.

Perovskite catalysts are produced by dissolving each component, acetate and nitrate, in a predetermined ratio in pure water and then evaporating to dryness (70-90"C) in accordance with a known manufacturing method. The product is then placed in an electric furnace and decomposed in an air atmosphere. , obtained by firing.

The structure of the obtained catalyst was confirmed to be perovskite by X-ray diffraction. This perovskite has a large specific surface area and high catalytic activity. The perovskite used in this example has a composition of Lao, 8Sr0.2cQo3.

Next, the same material 6 to 6 as the carrier is applied to the surface of the carrier produced earlier.
10 wt % of perovskite, 1 to 30 wt % of perovskite, and water were mixed, applied, and then dried (sintered at 800''C to form a homogeneous catalyst layer on the surface of the carrier to obtain a catalyst body.

Table 1 shows the supported amount (wt%) of various perovskite catalysts.
Shown below.

Table 1 The above five types of catalysts were prepared, and their
The nitrogen dioxide purification ability at 7oo''c and the carbon monoxide purification ability at 400°C were measured, and the results are shown in Figures 1 and 2, and the measurement conditions for each purification ability are shown in Table 2.

Table 2 As shown in Figure 1, the vapor 1 of Example has a large amount of perovskite supported, so its activity is very high even at low temperatures, and the oxidizing ability is fully exhibited, and NO2- and NO reactions do not occur at all, resulting in NO2 Instead of purifying the NO, it oxidizes the NO and generates the toxic gas NO2. This tendency can be seen in Example &2. It becomes smaller as it becomes tli3. However, in Example &4.45, since the supported amount is low and unsupported, the activity of the perovskite is absorbed by the NO2 purifying ability of the carrier itself at low temperatures, making it possible to purify NO2 even at low temperatures. For example, at a high temperature of 700°C, a supported amount of 1 wt% shows a NO2 purification rate of 50 to 60% regardless of the supported amount, and a supported amount of 1 wt% or less shows an NO2 purification rate of about 40%.
It can be seen that the values are as low as below.

Next, as shown in Figure 2, the purification ability of CO (CO2
(ability to oxidize to The slight decrease in purification ability is not a problem related to the activity of the perovskite itself, but is thought to be due to a decrease in the amount of supported perovskite, which causes the specific surface area of the catalyst to become smaller, resulting in a smaller active surface area. Since the CO purification ability is required to be 60% or more from a practical standpoint, the amount of perovskite supported is preferably 1 wt% or more. However, if the supported amount becomes too large, 41.
&2 has strong oxidizing power from No to No2 at low temperature,
In order to not purify No2 but to increase it,
From FIG. 1 and FIG. 2, it can be concluded that the optimum amount of perovskite supported is in the range of about 1 to 5 wt%.

Effects of the Invention As described above, the present invention provides N
02 In terms of purification ability, N
It is possible to obtain a catalyst body for exhaust gas purification that improves O2 purification ability and exhibits high purification efficiency in N02 purification ability at high temperatures and CO purification ability at low temperatures.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the amount of perovskite supported and nitrogen dioxide purification ability in an example of the present invention, and FIG. 2 is a characteristic diagram similarly showing the relationship between the amount of perovskite supported and carbon monoxide purification ability. be. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (2)

[Claims] (1) A catalyst body in which a mixture catalyst layer of a composite oxide of a rare earth element having a perovskite structure and a material having the same composition as the carrier is formed on a heat-resistant porous carrier, and the amount of perovskite supported is about 1% of that of the catalyst body. A catalyst body for exhaust gas purification with a concentration of ~5 wt%. (2) A catalyst for exhaust gas purification according to claim 1, in which a mixture of a composite oxide of a rare earth element, the same material as the carrier, and a solvent is applied to the surface of a heat-resistant porous carrier, dried, and fired. Medium.