JPS58170540A - Preparation of exhaust gas purifying catalyst - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a catalyst for purifying exhaust gas of an internal combustion engine.
related.

As a method for producing an exhaust gas purification catalyst, for example, a cordierite base material for a catalyst carrier is immersed in a slurry containing alumina, and then dried to form an activated alumina layer on the surface of the catalyst carrier base material. A base material for a catalyst carrier having an active atomizing layer is immersed in an aqueous solution of a predetermined concentration of one or more compounds of catalytic metals such as chloroplatinic acid, palladium chloride, and rhodium nitrate. A method of obtaining a catalyst by impregnating a layer with an aqueous solution and then weighing the dry fI is conventionally known.゛Among the catalysts thus obtained, palladium (hereinafter referred to as Pd)-platinum (hereinafter referred to as ?*)-rhodium (hereinafter referred to as Rh
) type catalysts have advantages over Pt-Rh type catalysts, such as less deterioration in an oxidizing atmosphere and a lower purification start temperature, but on the other hand, they deteriorate significantly in a reducing atmosphere and are susceptible to phosphorus and lead poisoning. When the exhaust gas temperature becomes high, the purification rate decreases to Pt.
-Rh type had disadvantages such as being lower than that of the catalyst.
``The present invention solves the above-mentioned drawbacks.
In other words, a base material for a monolithic cordierite carrier, for example, is immersed in a slurry containing alumina, the slurry inside the cell is blown away by a slight air current, and after drying, it is immersed in an aqueous solution of a compound containing Pd. , and drying to obtain an activated alumina layer A containing Pd. Next, the above alumina slurry is immersed again, and an activated alumina layer containing no noble metal is placed on top of the Pd-containing alumina layer.
Obtain 1 IB. This is immersed in an aqueous solution of a compound containing Pt and/or Rh, and activated alumina IIB is impregnated with Pt and/or Rh in the same manner as above. Through these steps, it is possible to obtain a catalyst in which the activated alumina layer Aiζ contains a large amount of Pd, and the active alumina layer B contains Pt and/or Rh.

The catalyst obtained by this production method has a higher purification rate than the Pt-Rh* catalyst, and has at least Pt
It has also become possible to reduce costs by replacing part of Pd with Pd).

Next, the present invention will be explained in detail with reference to the following examples.

Example 1 210 g of alumina sol with alumina content IQwt%
.

ll0wt% aluminum nitrate aqueous solution 5g, ion exchange water 60g
g was added and stirred to form a slurry.

A cordierite monolith carrier base material was immersed in this slurry for 1 minute, and the slurry inside the cell was blown off with an air current, dried at 200°C for 1 hour, and then immersed at 700°C in an aqueous palladium chloride solution for 1 hour.

It was dried at 200° C. for 1 hour to support Pd on the alumina layer Aiζ.

Furthermore, by using an alumina slurry having the same composition as above and performing the same operation, alumina containing Pd was obtained.
! A top layer A and an alumina layer B containing no noble metal were formed.

This was immersed in a dinitrodiaminoplatinum aqueous solution 2 and a rhodium chloride aqueous solution for 1 hour each, and dried at 200° C. for 1 hour to make the alumina layer B support Pt and Rh, thereby obtaining a catalyst 1.

Analysis of this catalyst revealed that the alumina layer AK was Pd,
Pt, Rh is 7# t +1lBKha Pt, Rh
It was found that 75% of Pt and Rh were present in the alumina layer B.

The precious metal content of this sample wIAa is shown in Table IIc.

Example 2 By the same operation as in Example 1, an alkaline layer A containing Pt1 as a lower layer was added to a cordierite-based substrate for a sonolith carrier.
An alumina layer B containing no noble metal was formed.

A comparative example prepared for comparing these examples with a conventional example is shown below.

Comparative Example 1 Using a slurry having the composition of Example 1 and W4, a cordierite base material for a sonolith carrier was immersed under the same conditions to form an alumina layer. At this time, the above operation was repeated twice in order to make the thickness of the acrylic layer the same as in the example. Add palladium chloride aqueous solution to this.

The catalyst was immersed in an aqueous solution of dinitrosyarseninoplatinum and an aqueous solution of rocum chloride for 1 hour each, and dried at 200 tons for 1 hour to obtain catalyst C. When this catalyst C was analyzed, it was found that Pt, Rh
, Pd was uniformly distributed within the alumina layer.

Table 1 shows the noble metal content of this catalyst C.

Comparative Example 2 An alumina layer was formed on a cordierite monolith carrier base material in the same manner as in Comparative Example 1. This was immersed in a dinitrodiaminoplatinum aqueous solution, followed by a rhodium chloride aqueous solution for 1 hour, and dried at 200°C for 1 hour.Table 1. Noble metal content in carrier IL The purification performance of these four types of catalysts a to d was tested by the following method, and their purification performance was evaluated.

In the durability test, a catalyst was installed in the exhaust system of a 6-cylinder 2800cc engine, and A/F (air fuel ratio - air volume/fuel weight)
+11b, S, V, (space velocity = gas flow rate passing through the catalyst per unit time/catalyst volume): The catalyst was operated at a catalyst bed temperature of 720° C. at 60,000 hours, and the purification rate of the catalyst was measured after 500 hours. sll constant voltage model gas.

c o 蓓o, s%# NO! ! 22001Fl#C
IHs! 8110P, O-OJ'/, , Ha
s 0.17%, HaO; 5%, the remainder was used.

The amount of model gas passing through the catalyst was set to 90,000 V in terms of S and V values.

The measured Co, HC, and NOd purification rates are shown in FIGS. 1 and 2.

Pt-P(1-Rh system (catalyst C) prepared by conventional method
Although the purification rate is higher at low temperatures than the Pt-Rh system (catalyst d), it is lower at high temperatures. It can be seen that the purification rate is higher than the pt-ith system (catalyst d) not only at the low temperature side (also at the high temperature side), and it improves the drawbacks of the conventional Pt-Pi-Rh catalyst. Although the activity of the Pt-Pd-Rh system (catalyst B) is inferior to that of the Pt-Pd-Rh system (catalyst C), the activity of the Pt-Pd-Rh system (catalyst C) and Pt-
It has better overall characteristics than the Rh type (catalyst d).

[Brief explanation of drawings]

FIG. 1 shows catalysts a and b according to Example 1.2 and catalysts according to Comparative Example 1.
The CO purification rates of catalysts c and d using 2IC are shown. FIG. 2 also shows the NO purification rates of samples #sm to d. Risail 1 6D CO of C and D
”! Iot normal temperature /l (c sugar 2 figure glaze butterfly α d~0 purification mochi-19: -

Claims (1)

[Claims] (1) After forming an activated alumina layer A on the surface of a substrate for a catalyst carrier, the alumina layer A is impregnated with an aqueous solution of a compound containing palladium, and after drying, an activated alumina layer is formed on the aluminum containing palladium. A method for producing an exhaust gas purifying catalyst, which comprises forming alumina layer B, impregnating the alumina layer B with an aqueous solution of a compound containing platinum and/or rhodium, and drying the alumina layer B.