JPS598421B2 - Catalyst for exhaust gas purification - Google Patents

Description

Detailed Description of the Invention The present invention provides an exhaust gas purification catalyst that can highly efficiently purify nitrogen oxides, carbon monoxide, and hydrocarbons, which are harmful components in exhaust gas emitted from internal combustion engines, etc. Regarding.

A variety of catalysts are currently being proposed for the purification of harmful components in exhaust gas as described above, and γ
- Using a chemically active porous material such as alumina or δ-alumina, and using a catalyst component consisting of lanthanum oxide or cerium oxide and platinum, palladium, etc. as the active carrier has relatively excellent purification activity. It is said to have the following.

However, as mentioned above, these conventional catalysts use chemically active substances such as activated alumina as a carrier, so if the catalyst is heated to a high temperature of 600°C or higher during use, A chemical interaction between the active support and the catalyst components takes place.

That is, at high temperatures, lanthanum oxide, which is a catalyst component,
Cerium oxide dissolves into the active carrier, resulting in a decrease in catalyst components and a decline in catalyst function.

The present invention has been made with the aim of overcoming such problems.

That is, the first invention of the present application provides chemically inert α-
Alumina is used as a carrier, and lanthanum oxide (La2
o3) as well as platinum (Pi) and palladium (
Pct) (hereinafter referred to as the first invention).

According to the first invention, since α-alumina, which is chemically inert, is used as a carrier, even if the catalyst is heated to a high temperature of 600°C or higher during use, the catalyst components and There is no chemical interaction between the carriers.

Therefore, it is possible to provide a catalyst that can maintain the catalytic activity of purifying the harmful components such as nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) even at high temperatures.

That is, since the above-mentioned support is chemically inert, unlike the above-mentioned conventional catalyst, the supported catalyst component lanthanum oxide does not react with the support and form a solid solution in the support even at high temperatures.

Therefore, the entire amount of lanthanum oxide having catalytic activity continues to exhibit its catalytic function as a catalytic component even at high temperatures, and the catalyst can maintain high purification activity.

This means that the lanthanum oxide in the second invention described below,
The same holds true for cerium oxide, and therefore the catalyst of the second invention can also maintain high purification activity.

As described above, the catalyst of the first invention has excellent high-temperature durability, and can exhibit high purification ability with a smaller amount of catalyst components than conventional catalysts.

In addition, the catalyst particularly has an air-fuel ratio (weight ratio of air to gasoline fed to the internal combustion engine) of 14.0 to 15.
It exhibits an excellent effect in simultaneously purifying the above-mentioned harmful components of exhaust gas from an internal combustion engine operated within a range of zero.

Furthermore, the second invention of the present application is one in which cerium oxide (Ce02) is added as a catalyst component to the catalyst according to the first invention, and lanthanum oxide and cerium oxide are added to chemically inert α-alumina. and an exhaust gas purifying catalyst supported with one or both of platinum and palladium.

According to the second invention, in addition to obtaining the same effects as the first invention, the presence of cerium oxide makes it possible to exhibit high purification ability over a wide range of air-fuel ratios from 13.5 to 15.5. can.

In addition, the diameter of the α-alumina flat plate in the carrier and 17 is 0.0
Preferably, it is 1 to 2μ.

If the average pore diameter is outside this range, it is difficult to exhibit excellent activity as an exhaust gas purifying catalyst.

Next, supporting the catalyst component on the porous body will be described.

First, lanthanum oxide is 1.0 to 100 g/13 per liter of carrier, and cerium oxide is similarly 1.0 to 100 g/l! It is preferable that

If the amount is less than the above amount, the purifying activity will be low, and if it is more than the above amount, no commensurate improvement in activity will be observed even if more is supported.

In addition, 1 liter of the above carrier is about 700 to 900 g in pellet form, and about 600 to 800 g in honeycomb form.
It is.

Regarding platinum and palladium, it is preferable that the weight (.9) of one or both of them is 0.01 to 50 g/13 per liter of carrier.

Below 0.019//l, the purification activity decreases,
If the amount is 50 g/11 or more, no commensurate improvement in activity will be observed even if the amount is loaded further.

Next, in supporting the above-mentioned catalyst components, as shown in the examples, raw materials for each catalyst component, such as lanthanum nitrate [L
a(NO3)3.6H20], lanthanum chloride [LaCl
3.7H20], cerous nitrate [Ce(N03)3
・6H20], cerous chloride C CeCd3 ・7
H20, l, palladium nitrate (Pd(NOs)2,
l, palladium chloride [PdCl2], platinum nitrate (P
t (NOq)4), chloroplatinic acid (H2Pt(J'6・
6H20], and the phase body is immersed in these solutions, dried, and fired.

By this firing, the above raw materials are changed into the corresponding lanthanum oxide, cerium oxide, platinum, and palladium, and are impregnated and supported on the carrier.

α-alumina used in the present invention includes γ-alumina,
1200' chemically active alumina such as δ-alumina
It can be obtained by heating above C.

Therefore, this α-alumina is chemically inert.

The shape of the carrier may be granular, columnar, honeycomb, or the like.

In addition, in the present invention, in order to save the alumina powder that is the constituent raw material of the carrier, as described above, a skeleton of granular bodies such as cordierite, honeycomb bodies, etc. prepared separately from the present invention is used as a matrix. It is also possible to construct a catalyst by coating and sintering the powder to form a carrier, and by supporting the catalyst component on the carrier.

Example 1 A catalyst according to the present invention was prepared using a spherical porous body of α-alumina as a phase body, and after conducting a durability test, its purification activity was measured.

That is, the above α-alumina carrier is prepared by heating a commercially available δ-alumina carrier (particle size: 3 myt) at 1200°C in an electric furnace.
It was made by firing for a time, and the specific surface area is 20 m/
It was g.

The α-alumina carrier thus produced is chemically inert as described above.

Next, the α-alumina carrier was immersed in an aqueous solution of the catalyst component raw materials shown below, dried, and calcined in air at 600°C for 3 hours to obtain various catalysts containing the catalyst components (Table 1). adjusted.

Next, the aqueous solution used when supporting the above catalyst component on the carrier is lanthanum oxide (La203), lanthanum nitrate, cerium nitrate (CeO2), platinum. In the case of platinum nitrate,
In the case of palladium, each aqueous solution of palladium nitrate was used.

In addition, when supporting the above catalyst component, after first supporting lanthanum oxide as described above, a method was taken in which cerium oxide and then one or both of platinum and palladium were sequentially supported in the same manner as above. .

In addition, each of the above-mentioned nitrates is changed by the above-mentioned calcination to become each of the above-mentioned catalyst components and supported in the carrier.

Next, in order to evaluate the durability of these catalysts, these catalysts were exposed to air-fuel ratios of 0 and 3 above and below the stoichiometric air-fuel ratio (A/F = 1 4.6) at intervals of 0.5 seconds. 800 in the exhaust gas from an internal combustion engine that was operated while changing
It was left at ℃ for 100 hours.

Also, at this time, the space velocity of the exhaust gas passing through the catalyst layer is 2
5,000/hour.

Next, the purification activity of the catalyst that had undergone the above durability test was evaluated.

That is, the above catalyst is filled in a quartz tube, heated and maintained at 350°C, and exhaust gas from an automobile internal combustion engine is poured into it.
It was introduced at a space velocity of 30,0007 hours.

The above exhaust gas moves the internal combustion engine around the stoichiometric air-fuel ratio, with an air-fuel ratio of 0.4 above and below it, every second? This was when the vehicle was operated while changing the conditions.

This change in air-fuel ratio has a wide range and a long period, so it is a more severe condition for measuring catalyst activity.

Note that the average concentration of harmful components in the exhaust gas during the above operation is approximately 0.0% of nitrogen oxides (NOx) in terms of volume ratio.
1%, carbon monoxide (Co) 0.8%, hydrocarbon (HC)
0.12%, carbon dioxide (CO) 12 pieces, hydrogen (H2
) 0. Part 2, Oxygen (02) 0.68 part, Water (H20
) 13 residual nitrogen (N2).

The purification activity was evaluated based on the rate at which the harmful components were removed (purification rate).

The results are shown in Table 2.

For comparison, these tables also show cases where lanthanum oxide and cerium oxide are not supported (catalyst &
S t ).

As can be seen from the above table, the catalyst according to the present invention using an α-alumina carrier has high purification activity.

Example 2 Regarding the catalyst according to the present invention, a durability test and a purification activity measurement were conducted in the case where the fluctuation range of the air-fuel ratio was further widened.

This test and measurement were conducted under conditions more severe than those in Example 1.

In other words, for the durability test, the air-fuel ratio was adjusted at 0.8 intervals every 1 second around the stoichiometric air-fuel ratio, and for the purification activity measurement, the air-fuel ratio was set at the same <0.
．． The results of measuring the purification rate were as follows:
It is shown in Table 3.

The target catalysts were those shown in Example 1, and their catalyst numbers are shown in Table 3.

The table only indicates the presence or absence of cerium oxide.

As is known from Table 3, the catalyst containing cerium oxide as a catalyst component (second invention) is different from the catalyst containing cerium oxide as a catalyst component (first invention).
It can be seen that a high purification rate is achieved even when the air-fuel ratio fluctuates over a wide range.

Comparative Example For comparison with the present invention, active alumina δ-alumina and γ-alumina were used as carriers, and the catalyst components according to the present invention were supported on the carriers in the same manner as in Example 1. , various comparative catalysts (Table 4) were prepared.

The above δ-alumina MJL: If. : Ji4tsu Akatsuki Fu≠ has a specific surface area of 79 ml g/g, and a spherical sintered body using i-alumina as a carrier has a surface area of 180 rty"/g and a pore volume of 0.68 cc/g.
It was g.

Note that the surface area of these supports is considerably larger than that of the α-alumina support according to the present invention (G).

Next, the purification activity of the above catalyst was measured in the same manner as in Example 1.

The measurement results of the purification rate are shown in Table 5.

As can be seen by comparing the results of the catalyst of the present invention in Table 5 above and Table 2 above, the catalyst using α-alumina as an inert carrier in the present invention can be compared with δ-alumina or γ-alumina. It can be seen that the purification activity is considerably higher than that of catalysts using chemically active catalysts.

Claims (1)

[Scope of Claims] 1. A catalyst for exhaust gas purification, characterized in that it uses chemically inert α-alumina as a carrier, and supports lanthanum oxide and one or both of platinum and palladium on the carrier. . 2. A catalyst for exhaust gas purification, characterized in that it uses chemically inactive α-alumina as a carrier, and supports lanthanum oxide and cerium oxide on the carrier, as well as one or both of platinum and palladium. .