JPS5920385B2 - Exhaust gas purification catalyst treated to prevent phosphorus poisoning - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for purifying exhaust gas from an automobile engine, and particularly to a catalyst treated to prevent phosphorus poisoning.

Automotive engine oil contains metal salts of dialkyldithiophosphates (as metals) as antioxidants and anti-wear agents.
However, it is known that the above-mentioned metal dithiophosphates have a poisoning effect on catalysts for purifying exhaust gas.

This poisoning effect is caused by the above-mentioned zinc dithiophosphate being burned in the engine to produce combustion ash of zinc phosphate, Zn(PO3)2, and this combustion ash is generated on the surface of the exhaust gas purification catalyst installed in the engine exhaust system. This is due to the fact that the adhering burnt ash vitrifies due to the high heat caused by the catalytic action and coats the catalyst surface, preventing contact between the catalyst and exhaust gas, and as a result, the exhaust gas purification performance is significantly reduced. be.

The present inventors studied the vitrification of the combustion ash and found that the vitrification phenomenon is influenced by the temperature at which the combustion ash is heated.

That is, when the above zinc dialkyldithiophosphate is heated for 2 hours, the combustion ash is spongy at a heating temperature of 600°C, and is partially vitrified at 800°C;
It is completely vitrified at ℃.

The combustion ash is vitrified by high heat in this way.
ZnO component and P2O5 in combustion ash (zinc phosphate)
This is because the molar ratio with the components is within a certain range.

As a result of various studies, he learned that if the molar ratio of P2O5 to metal oxides such as ZnO is below a certain limit under high temperatures during the combustion ash generation process, vitrification will not occur even under high heat, and he completed this invention. That's what I came to do.

That is, the present invention provides a catalyst for engine exhaust gas, in which P of combustion ash contained in the exhaust gas and attached to the catalyst surface is reduced.
The surface of the catalyst is coated with ZnO in an amount of 1~loog per 11 catalysts in an amount such that the quantitative ratio of 2O5 and ZnO, which is a vitrification-inhibiting metal oxide, exceeds the range in which combustion ash can be vitrified. This is an exhaust gas purification catalyst that has been treated to prevent phosphorus poisoning.

The minimum ratio of P2O5, which can form glass in the combustion ash deposited on the catalyst surface during engine operation, and ZnO, which is a vitrification-inhibiting metal oxide, is 36 mol% of P2O to ZnO+P2O5.

In addition to ZnO, C
Examples include oxides of alkali metals such as aO, MgO, and BaO, but since the combustion ash contains Zn components, the power of ZnO blends well with the combustion ash, and ZnO has a phosphorus poisoning prevention effect. is superior to the above-mentioned alkali metal oxides.

Platinum,
Noble metals such as rhodium are attached to a monolithic carrier or are used in the form of pellets.

The catalyst includes an oxidation catalyst that oxidizes and burns reducing substances such as hydrocarbons and carbon monoxide contained in exhaust gas,
In addition to the above oxidation effect, NOx contained in exhaust gas
A redox catalyst is used to reduce the oxidation-reduction catalyst.

The amount of the combustion ash of the metal dithiophosphate that poisons the catalyst varies depending on the type and form of the catalyst. Measure the amount of phosphorus component attached when the amount of phosphorus component decreases due to poisoning, and attach ZnO to the catalyst in advance so that the above-mentioned combustion ash becomes the minimum ratio of P2O5 and ZnO that can be vitrified, corresponding to the amount of phosphorus component attached. Let it be.

The amount of ZnO deposited is 1 to 100 g, preferably 1 to 30 g per liter of catalyst.

The lower limit of the above range assumes that the effect of phosphorus poisoning starts to appear when 0.1% by weight of phosphorus is deposited, and the upper limit of the above range is determined by experimentally determining the upper limit of the amount of phosphorus deposited at 2.0% by weight of phosphorus. This is the basis for the calculation.

When the amount of ZnO deposited above is smaller than the lower limit, the combustion ash becomes vitrified when the phosphorus poisoning is large, and a poisoning phenomenon occurs; This is not preferable because not only the preventive effect is saturated, but also the amount of ZnO that covers the active surface of the catalyst increases.

In order to attach ZnO to the surface of the catalyst, the catalyst is immersed in an aqueous solution of the metal, such as a metal nitrate or acetate, and then dried and fired.

This invention will be explained in detail below.

Example 1 Molded from cordierite, 48 hexagonal holes/d
Platinum was deposited on a monolithic carrier having a diameter of 25.4 mm and a length of 50 stages (catalyst volume of 24 mm) at a rate of 1.6 E//l, and the catalyst was further immersed in an aqueous zinc nitrate solution and fired. A catalyst was prepared whose surface was coated with Zn052971.

This catalyst was mixed with 1 part of commercially available zinc alkyl dithiophosphate and 4 parts of kerosene.
After immersing the catalyst in a mixed solution of
A phosphorus-poisoned catalyst sample was prepared using 99.6 g of Zn(PO3) per sample.

For this catalyst sample, the air/fuel ratio was 16. The exhaust gas obtained by burning the O mixture is heated at a gas flow rate of 161/min and a space velocity of 40
,000 hours, and the purification rate for hydrocarbons was measured.

For comparison, the purification rate was measured in the same manner as above using a catalyst not coated with ZnO.

The above measurement results are shown in the graph of FIG.

As can be seen from the graph in Figure 1 above, catalyst A coated with ZnO (solid line) is different from catalyst B coated with Zr]O (dotted line).
Compared to , the purification rate does not improve unless the temperature is slightly higher before phosphorus poisoning, but the purification effect against phosphorus poisoning is excellent and there is little decrease in purification efficiency.

Example 2 Purification was carried out in the same manner as in Example 1, except that instead of platinum in Example 1, a redox catalyst having a mixture of 10 parts platinum and 1 part rhodium attached at a ratio of 129/l was used on the monolithic carrier. The ratio was measured and the results are shown in the graph of FIG.

As can be seen from the graph in FIG. 2, a purifying effect having the same tendency as in FIG. 1 can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between catalyst inlet temperature and HC purification rate in Example 1, and Figure 2 is a graph showing the relationship between catalyst inlet temperature and HC purification rate in Example 2.
This is a graph showing the relationship with the purification rate. In the above graph, solid lines A and a are for catalysts coated with ZnO, dotted lines B and b are for catalysts that are not coated with ZnO, A and B are before phosphorus poisoning, and a and b are for catalysts coated with phosphorus. It shows after being poisoned.

Claims (1)

[Claims] 1. In a catalyst for purifying engine exhaust gas, the quantitative ratio of P2O5 in the combustion ash contained in the exhaust gas and attached to the catalyst surface to ZnO, which is a vitrification-inhibiting metal oxide, exceeds the range in which the combustion ash can be vitrified. Excessive amount of catalyst
1-100 per hit. ! An exhaust gas purifying catalyst subjected to phosphorus poisoning prevention treatment, characterized in that the catalyst surface is coated with i' ZnO in advance.