JPS60238147A - Catalyst for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain a catalyst capable of purifying nitrogen oxide in exhaust gas exhausted especially from an internal combustion engine in a wide range of an air/fuel ratio with high efficiency, by supporting the group IIIa element and Pd of the Periodic Table by a porous carrier. CONSTITUTION:The group IIIa element (e.g., Ce) and Pd of the Periodic Table are supported by a porous carrier such as alumina in such a ratio that the group IIIa element is 0.01-1.0mol per 1l of the porous carrier and Pd is 0.02-10g per 1l of said carrier. The catalyst can purify nitrogen oxide with high efficiency and especially can purify nitrogen oxide in exhaust gas of a car in a wide range of an air/fuel ratio with high efficiency. Even in such a state that oxygen is excessively present in exhaust gas, nitrogen oxide can be purified with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst that can efficiently purify nitrogen oxides, particularly nitrogen oxides in exhaust gas discharged from internal combustion engines and the like.

[Conventional technology]

In recent years, exhaust gases emitted from internal combustion engines of automobiles contain harmful components such as nitrogen oxides, carbon oxides, and hydrocarbons, which have become a cause of air pollution. Therefore, this exhaust gas purification is being studied in various fields.

One of the methods for purifying this exhaust gas is to use a catalyst such as the one of the present invention to remove the above-mentioned harmful components, and to convert the oxygen into carbon dioxide by reacting with the above-mentioned carbon oxide. Do the following.

Hitherto, the above-mentioned oxidation catalysts have been developed which have great effects, but the above-mentioned reduction catalysts for treating nitrogen oxides have not yet been developed which are sufficiently effective.

In other words, as catalysts for purifying nitrogen oxides in exhaust gas, catalysts in which precious metals such as palladium, platinum, and rhodium are supported on a carrier made of a porous material such as alumina are used because they have high catalytic activity. . However, these catalysts cannot efficiently purify nitrogen oxides over a wide range of air-fuel ratios, such as in the exhaust gas of automobiles. especially.

When the ratio of air to fuel (air-fuel ratio) increases.

Oxygen is contained in excess of the amount required to completely burn the unburned components, and such an oxygen-rich state is an adverse condition for the purification of nitrogen oxides.

In other words, under conditions where oxygen is excessive, hydrogen or reducing substances such as oxidant monoxide, which should react with nitrogen oxides in the exhaust gas, preferentially react with oxygen, and nitrogen oxides are not removed. remains.

[Problem that the invention seeks to solve]

As mentioned above, in order to purify nitrogen oxides in exhaust gas from automobiles, etc., it is necessary to develop a catalyst that can perform the purification efficiently even in a state where the air-fuel ratio is high.

The present invention has been made to solve these problems.

[Means for solving problems]

It is characterized by:

In the present invention, the above-mentioned Group Ⅰα elements include:

Scandium (8c), Yttrium (Y), =77
Tan (Lα), cerium (Oe), praseodymium (Fr
), Neodymium (Nd), Summer IJ UA (8m
).

There are europium (Eu), gadolinium (Gd), tilbium (Tb), dysprosium (In), holmium (no), erbium (Er), thulium (Tm), ytterbium (Yb), yvffflm (Lu), etc. , generally called rare earth elements.

The supported amount of the mα group element is preferably in the range of 0.01 to 1.0 mol based on the porous carrier 11.

If it is less than 0.01 mol, there is no sufficient purifying activity, and the number of MIL
The effect of supporting group elements is small. Further, as the supported amount increases, the purifying activity improves, but even if more than 1.0 mol is supported, a commensurate purifying activity cannot be obtained.

Furthermore, it also inhibits the catalytic action of coexisting palladium.

Furthermore, palladium supported on the porous carrier also acts as a catalyst component for purifying nitrogen oxides. The amount supported is preferably within the range of 1102 to 10 f per 17 of the porous carrier 11. If the supported amount is less than 0.021 g, the purification activity will be low, and if it is more than 10 g, no commensurate improvement in activity will be observed even if the supported amount is more than 10 g.

The carrier in the present invention includes alumina (A40),
Magnesia (MgO), Alumina Magne V 7 (
MgAj? t 04 ) Spinel, diy=+=7(Z
r02) @, and it is made into a porous body to improve the 1111 media activity. The porous body is preferably a sintered body obtained by sintering the raw material powder. This sintered body has high strength and high mechanical durability.

The method for supporting the group (1) alpha group element and palladium on the porous carrier is preferably carried out as follows. ■ The α-group element is supported on the carrier using nitrate.

A compound of a group IV element such as a chloride is dissolved in a solvent such as water or alcohol, and the carrier is immersed in the solution to impregnate the carrier with the solution. After drying, the compound is heated to form a group IV element. This is carried out by impregnating and supporting a carrier. Further, palladium is also supported in the same manner as above. In addition, Part ■
The carrier is immersed in a solution containing an α-group element compound and palladium.

The solution may be impregnated into a carrier.

In addition, the catalyst according to the present invention is a granular body, a pellet-like body,
Although its shape and structure are not limited, such as a honeycomb-like structure, there are cases where it is a honeycomb-like structure.

The surface area per unit volume of the catalyst is increased, and the purification activity is particularly high.

〔Effect of the invention〕

According to the catalyst of the present invention, nitrogen oxides can be purified with high efficiency, and in particular nitrogen oxides in automobile exhaust gas can be purified with high efficiency over a wide range of air-fuel ratios.

Further, even in a state where an excessive amount of oxygen exists in the exhaust gas, nitrogen oxides can be purified with high efficiency. Although the reason for this is not clear, a large amount of nitrogen oxides are adsorbed on the catalyst surface due to the action of the α-group elements, even when the oxygen concentration is high.

It is thought that this is because reducing substances such as hydrogen or arsenic monoxide selectively react with this nitrogen oxide.

Note that the catalyst according to the present invention can be used not only in internal combustion engines such as automobiles, but also as a catalyst for purifying nitrogen oxides in exhaust gas from nitric acid factories and the like.

〔Example〕

The present invention will be explained in detail below.

An α-alumina spherical porous body serving as a carrier is impregnated with an aqueous solution of a nitrate of a group ① α element at a predetermined concentration.

After drying, it was heated in the air at 600°C for 6 hours to decompose the nitrates of group ①α elements into group ①α elements.

0.1 m4kg of the Pla group element was supported on each carrier 11. Subsequently, the above-mentioned carrier was impregnated with an aqueous solution of palladium nitrate, and after drying, it was heated in the air at 600°C for 3 hours to support 1f of palladium per 11 carriers. ~15) was obtained. Table 1 shows the types of group ①α elements in the catalyst. In addition, for comparison, a comparative catalyst (catalyst A31) was also prepared in which only palladium was supported in the same manner as above without supporting the group ①α element (catalyst A31).

When evaluating the purification activity of the obtained catalyst,
First, a durability test of the catalyst was conducted in advance. That is, the temperature of the exhaust gas from an internal combustion engine (an engine using gasoline as fuel) in which the catalyst is operated at a stoichiometric air-fuel ratio (approximately 14.6)
A durability test was conducted at 50° C. and a space velocity of 25,000/hour for 100 hours.

Next, in order to evaluate the purification activity, the nitrogen oxide (NOx) and oxygen (02) removal rates of the catalyst were measured.

That is, the above catalyst was filled in a quartz tube as a reaction tube, and the quartz tube was operated at a space velocity of 50,000/hour and a stoichiometric air-fuel ratio while heating from room temperature to 500° C. at a temperature increase rate of 4° C./min. Exhaust gas from automobile internal combustion engines was introduced. The concentration of each component in the exhaust gas during the above operation is as follows:
By volume ratio, nitrogen oxide 0.1%, -carbon oxide 0.8%,
Hydrocarbon α12%.

12% ash dioxide, 0.2% hydrogen, 68% oxygen α.

It was 16% water and the balance was nitrogen. Thereafter, the NOx and 02 removal rates were measured for each catalyst.

FIG. 1 takes the catalyst of the catalyst layer 2 as an example, and plots the temperature of the catalyst layer on the horizontal axis, NOx, 0. The purification activity is illustrated with the vertical axis representing the removal rate. Furthermore, the results were organized in terms of the selectivity of the NOx and O- removal rates in each catalyst layer, and the second
In the figure, 01 removal rate is plotted on the horizontal axis.

The NOx removal rate is plotted on the vertical axis. In FIG. 2, area 8 (NOx) of the part surrounded by the diagonal line and the upper curve (the part with excellent NOx removal rate).

Then, measure the area 5 (01) of the part surrounded by the diagonal line and the lower curve (the part with excellent removal rate of 02).

The ratio was set at 8 (NOx)/8 (Os). S
The larger the value of the (N0x)/5(O2) ratio, the higher the NOx removal rate.

Also, from the measurement results for the comparative catalyst (catalyst layer 81),
Figure 3 shows the relationship between the catalyst layer temperature and the removal rate of NO,,0, and Figure 4 shows the selectivity of the removal rate of NOx and NOx.
Shown in the figure. Also, from Figure 4, the above 8(NOx)/8
We calculated the (0,) ratio.

The 8(NOx)/8(OM) ratio for each catalyst was measured and the results are shown in Table 2.

As is clear from Table 2, the catalyst according to the present invention is 8
(N0x)/8 (o,) ratio shows a high value of 0.51 to 1.68, while the comparative catalyst (A81) has a ratio of 0.1 to 1.68.
The catalyst of the present invention showed a significantly low value of 3.

[Brief explanation of drawings]

Figures 1 and 5 are the NOx and 0 removal rate curves for catalysts KA2 and KA81 in Examples, and Figures 2 and 4 are for catalyst F.
X2 and 81 NOx and 0! It is a figure which shows the removal rate relationship curve with. Applicant Toyota Central Research Institute Co., Ltd. Patent Attorney Yoshiyasu Takahashi (2 others)

Claims (4)

[Claims] (1) A catalyst for removing nitrogen oxides, comprising a porous carrier supporting an element of group 1 [A of the periodic table] and palladium. (2) The porous carrier is alumina or magnesia. The catalyst for removing nitrogen oxides according to claim 1, which is one or more of alumina, magnesia spine A/, and zipconia. (3) Group ■α elements of the periodic table are contained in the porous carrier 11
The catalyst for removing nitrogen oxides according to claim (1), wherein 0.001 to 1.0 mol of nitrogen oxides are supported on the catalyst. (4) The catalyst for removing nitrogen oxides according to claim (1), wherein the palladium is supported on a porous carrier 11 in an amount of α02 to 10 g.