JPH04187240A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To maintain purifying performance and hydrogen sulfide controlling performance over a long period of time by coating the surface of the base material of a carrier with a catalyst carrying layer consisting of Fe-Ti double oxide and activated alumina, and supporting a catalytic metal on the supporting layer. CONSTITUTION:The surface of the base material of a carrier is coated with a catalyst carrying layer consisting of Fe-Ti double oxide such as FeTiO2 or FeTiO3 and activated alumina such as gamma-Al2O4 mixed preferably in about 0.005-0.4 weight ratio of the double oxide to the activated alumina. A catalytic metal such as Pt or Rh is then deposited on the catalyst supporting layer. Purifying performance and hydrogen sulfide controlling performance can be maintained over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust gas purifying catalyst that is disposed in an exhaust system of an internal combustion engine and purifies exhaust gas.

[Prior art] Conventionally, exhaust gas purification catalysts have been produced by forming a catalyst support layer made of activated alumina on the surface of a carrier base material, and supporting a catalyst metal such as platinum, rhodium, or palladium on the catalyst support layer. something is known. This exhaust gas purification catalyst oxidizes and purifies hydrocarbons (HC> and -carbon oxides (Co) contained in exhaust gas, and converts nitrogen compounds (N
It is purified by reducing Ox>.

By the way, when fuel containing sulfur is used, the exhaust gas contains sulfur dioxide gas (802).

This sulfur dioxide gas is adsorbed and accumulated on the catalyst support layer. However, under certain conditions, a reduction reaction occurs on the surface of the catalyst, and the exhaust gas from the catalyst may contain hydrogen sulfide gas that gives off a bad odor. For example, when the engine is under high load, controls such as stopping the introduction of secondary air or increasing the amount of fuel are performed in order to prevent the catalyst from overheating. At this time, the air-fuel ratio (A/F) of the exhaust gas in the catalytic converter becomes a rich atmosphere with excess fuel (F), and the sulfur dioxide gas adsorbed on the support layer is reduced and reacts to become hydrogen sulfide (H2S). is known to occur.

This reaction tends to occur when the catalyst bed temperature is at a high temperature of 600'C or higher, and under adverse conditions such as a high sulfur content in the fuel, foul-smelling exhaust gas may be emitted.

For example, Japanese Patent Application Laid-Open No. 63-116742 discloses the use of Δ, O, Ce, and Co as a fire-resistant carrier base material.

An oxide coat layer containing at least one of Ni and Fe and 1-a is formed, and Pt, P
d, supporting at least one noble metal of Rh l-12
An exhaust gas purifying catalyst that suppresses the generation of No. 3 has been disclosed.

[Problems to be Solved by the Invention] The function of the exhaust gas purifying catalyst disclosed in the above-mentioned publication is to purify HC, Co, and NOX, and to suppress the emission of H2S. In other words, this catalyst contains F
A metal consisting of at least one of e, Ni, and Co is contained alone as an oxide, and these metal oxides
The aim is to suppress 2S emissions. However, these metals tend to sinter with alumina. For this reason, these metals sinter with the alumina containing them due to thermal history, and the crystal form of alumina and the crystal form of the metal elements change.
There were problems such as a decrease in purification performance and a decrease in hydrogen sulfide suppression performance.

The present invention was made in view of these circumstances, and
The purpose is to maintain purification performance and hydrogen sulfide suppression performance for a long period of time.

[Means for Solving the Problems] The exhaust gas purifying catalyst of the present invention comprises a carrier base material, a catalyst support layer coated on the surface of the carrier base material, and a catalyst metal supported on the catalyst support layer. In the gas purification catalyst, the catalyst support layer is composed of a composite oxide of iron and titanium and activated alumina.

As the carrier base material, a honeycomb-shaped monolith carrier base material,
Conventionally known materials such as pellet carrier base materials and metal carrier base materials can be used as they are. The same materials as conventional ones can be used, such as ceramics such as cordierite, mullite, alumina, and spinel, and heat-resistant metals such as ferritic steel.

The most important feature of the present invention lies in the structure of the catalyst support layer.

That is, the catalyst support layer is composed of a composite oxide of iron and titanium and activated alumina. For example, γ-A, 0203 is used as the activated alumina. Further, as a composite oxide of iron and titanium, for example, FeT i 02
, FeT i 03, etc. are used. This catalyst support layer is formed by mixing composite oxide powder and activated alumina powder and firing the mixture. Here, the composite oxide powder can be produced by absorbing a solution in which a titanium compound is dissolved in iron oxide, followed by drying and firing. It can also be produced by absorbing a solution in which an iron compound is dissolved in titanium oxide powder, or it can be produced by co-precipitating iron and titanium from a solution in which both titanium and iron compounds are dissolved. You can also.

Various mixing ratios can be selected between the composite oxide of iron and titanium and activated alumina, but in terms of weight ratio, the composite oxide/activated alumina
The range of activated alumina from 0.005 to 0.4 is particularly preferred. When the amount of complex oxide exceeds the amount of activated alumina,
The amount of catalytic metal supported decreases, resulting in deterioration of catalytic performance.

Furthermore, if the amount of composite oxide is too small, it will be difficult to suppress hydrogen sulfide.

A catalyst metal is supported on the catalyst support layer as in the conventional case. Typical examples of the catalytic metal include platinum, rhodium, and palladium, and it is preferable to use at least one of these. In addition, noble metals such as iridium, ruthenium, and osmium, or base metals such as chromium, nickel, vanadium, copper, cobalt, and manganese can also be added. This catalyst metal is supported on the catalyst support layer. The supported amount can be variously selected depending on conditions such as desired performance and cost, as in the past.

[Operations and Effects of the Invention] In the exhaust gas purifying catalyst of the present invention, a composite oxide of iron and titanium is contained in the catalyst support layer. That is, since the catalyst supporting layer is formed from activated alumina powder and composite oxide powder, the reaction between each metal element and alumina is suppressed during firing or use. Therefore, the crystalline form does not change even when subjected to thermal history, so the initial purification performance and hydrogen sulfide suppression performance are maintained for a long period of time.

That is, since the exhaust gas purifying catalyst of the present invention contains the Fe-Ti composite oxide in the catalyst support layer, it not only traps sulfur content on the lean side but also efficiently traps sulfur content on the rich side. Furthermore, on the rich side, H2 combines with sulfur.
Since it traps H2S, almost no H2S is generated.

Therefore, according to the exhaust gas purifying catalyst of the present invention, it is possible to maintain the same purification performance as the initial level for a long period of time, exhibit high purification performance, and suppress the generation of H2S.

[Example] (Example 1) Hereinafter, the manufacturing method will be explained instead of explaining the structure of the exhaust gas purifying catalyst of this example.

Titanium trichloride aqueous solution (titanium trichloride 13.4% by weight) and 80 parts by weight of iron oxide powder were brought into contact, and then heated at 100°C.
The powder is then dried at 750° C. for 1 hour to form a composite oxide powder of iron and titanium.

This powder contains iron and titanium in a molar ratio of Fe:Ti=1
: Contained at a ratio of 1.

γ-alumina powder, aluminum nitrate solution, cerium oxide powder, alumina sol, and water are added to this composite oxide powder and thoroughly mixed and stirred to form a slurry. This slurry is brought into contact with a cordierite honeycomb carrier base material and excess slurry is blown off, then dried at 100°C and then fired at 700°C for 1 hour to form a catalyst support layer. Further, the dinitrodiammine platinum solution and the rhodium chloride aqueous solution are brought into contact and calcined to support platinum and rhodium, thereby obtaining the exhaust gas purifying catalyst of Example 1.

The composition of this catalyst is: carrier base material 1ρ bridge, alumina 120C
I, cerium 0.3 mol, iron 0.1 mol, titanium 0.1
Mol, platinum 1. O (J and rhodium 0°20.

(Example 2) Instead of mixing titanium trichloride solution and iron oxide powder,
A catalyst of this example was obtained in the same manner as in Example 1, except that a composite oxide powder was formed by bringing an iron nitrate aqueous solution into contact with a titanium oxide powder and firing the mixture.

The composition of this catalyst is the same as in Example 1.

(Example 3) To form a composite oxide powder, aqueous ammonia is gradually added to an aqueous solution in which titanium trichloride and iron chloride are dissolved in a molar ratio of 1:1 to co-precipitate titanium and iron. A catalyst of this example was obtained in the same manner as in Example 1 except that this coprecipitate was calcined to obtain a composite oxide powder. The composition of this catalyst is the same as in Example 1.

(Example 4) The same as Example 1 except that palladium chloride was used instead of dinitrodiammine platinum and palladium was supported instead of platinum. In this case, the amount of palladium supported was 1.0 g per 1.11 of the carrier base material, and the other components were the same as in Example 1.

(Example 5) An exhaust gas purifying catalyst was obtained in the same manner as in Example 2 except that palladium was supported instead of platinum. The amount of palladium supported was 1.0 g per 1.rho. of the carrier base material, and the other components were the same as in Example 1.

(Example 6) The same as Example 3 except that palladium was supported instead of platinum. The amount of palladium supported is 1ρ on the carrier base material.
The other components are the same as in Example 1.

(Comparative Example 1) The same as Example 1 except that the composite oxide powder was not used and iron oxide powder was used instead.

The composition of this catalyst was the same as in Example 1 except for titanium.

(Comparative Example 2) Same as Comparative Example 1 except that palladium was supported instead of platinum. The composition of this catalyst was the same as in Example 4 except for titanium.

(Test Example) The catalysts (1,3 J) of each of the above Examples and Comparative Examples were
00cc, connected to the exhaust system of an in-line 4-cylinder engine, operated for 1 hour at an inlet gas temperature of 600°C and A/F = 13.0, then switched to A/F = 15.0 and maintained that state for 5 minutes. During this period, the average hydrogen sulfide temperature in the gas passing through the catalyst was measured. The results are shown in Table 1. It can be seen from Table 1 that the concentration of hydrogen sulfide is much lower in the catalysts of Examples than in the catalysts of Comparative Examples. This is clearly due to the use of composite oxide powder of iron and titanium.

Table 1 (Durability test) Catalysts (1, 3, 0) of each of the above examples and comparative examples were
It was connected to the exhaust system of a 00cc inline 4-cylinder engine and operated for 200 hours at an input gas temperature of 900°C and an A/F = 14.6. Thereafter, the temperature characteristics of each catalyst degraded at A/F=14.6 were measured. The results are shown in Table 1. From Table 1, it can be seen that the catalysts of the Examples have a lower 50% hydrocarbon purification temperature than the Comparative Examples, and have excellent durability. It is clear that this is due to the use of composite oxide powder of iron and titanium.

Patent applicant: Toyota Motor Corporation

Claims (1)

[Claims] (1) In an exhaust gas purifying catalyst comprising a carrier base material, a catalyst support layer coated on the surface of the carrier base material, and a catalytic metal supported on the catalyst support layer, the catalyst support layer is made of iron and An exhaust gas purification catalyst characterized by being composed of a titanium composite oxide and activated alumina.