JPH02135143A - Production of catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst having high NOx removing performance by adhering a gel soln. prepd. by mixing starting materials for synthesizing zeolite to a metal carrier, carrying out heating under pressure and calcining to form a zeolite layer and supporting a catalytically active metal on the zeolite layer. CONSTITUTION:A gel soln. prepd. by mixing starting materials for synthesizing zeolite such as alkali, alumina and silica is adhered to a metal carrier 1. This carrier 1 is put in a hermetically sealed vessel and heated with steam at about 80-350 deg.C under about 0.1-20kg/cm<2> pressure for about 10-100hr to crystallize zeolite. The carrier 1 is then cooled, washed, dried and calcined at about 400-700 deg.C to form a zeolite layer 3 on the carrier 1 and a catalytically active metal such as Cu is supported on the zeolite layer 3. The resulting catalyst removes NOx at a high rate even in an air contg. oxygen in excess in a lean air-fuel ratio.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a catalyst for purifying automobile exhaust gas, and particularly to a method for producing a catalyst that can purify NOx at a high rate even in an oxygen-rich atmosphere with a lean air-fuel ratio. It is something.

<Prior art> The following catalysts are used to purify Co (carbon oxide), HC (hydrocarbon), and NO (nitrogen oxide), which are harmful components in automobile exhaust gas. Or known: ■ A catalyst in which an activated alumina coat layer is formed on a cordierite honeycomb carrier to support noble metals, rare earth oxides, etc.
(Refer to Publication No. 5, etc.), ■Metallic honeycomb carrier A catalyst in which an activated alumina coating layer is formed on a so-called metal carrier to support precious metals, rare earth oxides, etc. (JP-A-56-96726, JP-A-57-6)
814:l, see Publication No. 57-7898, etc.), ■Catalyst in which a zeolite coat layer is formed on a cordierite honeycomb carrier and Cu is supported by ion exchange (JP-A-59
-2:16642, Publication No. 60-125250, etc.).

These various catalysts have conventionally been manufactured as follows. That is, a slurry obtained by mixing and stirring alumina or zeolite powder, binder, water, etc. is wash-coated on a cordierite honeycomb carrier or metal carrier, and after firing to obtain a coated carrier, it is coated with PL, which is a catalytically active component. , Pd, Rh': p noble metal or C
It is produced by supporting a catalytically active metal on the coated carrier by immersing it in an aqueous solution of a transition metal such as u and drying it.

The catalyst in the above ■■ is stoichiometric (stoichiometric air-fuel ratio A/F = 14.
However, it has the disadvantage that it is difficult to remove NOx in an oxidizing atmosphere on the lean side. In terms of purifying NOx on the lean side, the Cu/zeolite catalyst mentioned above is superior.

<Problem to be solved by the invention> However, at present, there is no catalyst that is fully satisfactory for purifying NO on the lean side. In particular, in recent years, efforts have been made to burn as lean a mixture as possible during normal driving in order to improve the fuel efficiency of automobiles, so the amount of NO emitted without being reduced and purified has tended to increase. NOx pollution has become an urgent and social problem. For this reason, there is a need for a catalyst that can purify NOx on the lean side at a higher rate.

On the other hand, in a method for manufacturing an exhaust gas purifying catalyst, there is a need for a new method for manufacturing a catalyst that enables significant catalyst reformation or cost reduction.

The present invention was made for the purpose of solving these problems, and the problem to be solved is a novel catalyst manufacturing method that makes it possible to produce a catalyst with high NOx purification performance at low cost. The goal is to provide the following.

<Means for Solving the Problems> The method for producing an exhaust gas purification catalyst of the present invention which solves the above problems is to apply a gel solution containing a mixture of alkali, alumina, silica, water and other raw materials for zeolite synthesis to a metal carrier. After being deposited, the zeolite layer is heated and pressurized in a gas phase in a closed container and fired to form a zeolite layer on the metal carrier, and then the catalytically active metal is supported on the zeolite layer.

The metal carrier used in the present invention is a roll type made by rolling up thin corrugated metal sheets, or a laminated type cell body in which corrugated metal sheets and flat metal plates are planted in layers. It may be of a general shape integrated with. However, it is important to use a material with an alumina film on its surface. Therefore, as a metal carrier metal material,
It is preferable to use a metal that forms an alumina film during the heat treatment for the above-mentioned integration, such as a Fe-(:r-AI alloy).In this case, the heat treatment conditions are as follows:
50-1200℃, degree of vacuum + 1O-2-10-6To
rr, heating time: 0.5 to 8 hr is appropriate. As a result, alumina is formed in the form of needles on the metal carrier.

The gel solution to be applied to the metal carrier may be a Na20-A12C1+ 5if2H20 gel solution obtained by mixing and stirring alkali, alumina, silica, water, alkali, etc. Common inorganic raw materials for gel solutions include sodium (meth)silicate (Na2Sign) silica gel (SiO
Oz), aluminum hydroxide (Al2O, -nl+2
0), sodium hydroxide (Mail(), etc.) as an organic base such as tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), tetraethylammonium (TBA).
``I can name nine.

To attach the gel solution to the metal carrier-h, for example, immerse the cleaned metal carrier in the gel solution to impregnate the gel solution into the carrier cells, pull it out, and then blow off the excess gel solution. You can do whatever is convenient for you.

In order to form a zeolite layer, the above gel solution-attached carrier is first placed in a closed container and heated to a temperature of 280°C using water vapor.
After crystallizing the zeolite by heating for 10 to 100 hours while maintaining the conditions of 0.1 to 20 Kg/am2 at ~350°C, the cooled material was thoroughly washed with water, and then heated at 80 to 150°C. Dry, then 400-700°C
You can bake it with

When supporting catalytically active metals on zeolite synthesized directly on a metal carrier, is it possible to support PL, Pd, Rh, etc. in accordance with a conventional method?
In order to obtain a catalyst that exhibits x purification performance, it is better to support Cu by ion exchange. This ion exchange is caused by Na” (and some 11+
etc.) to Cu, and this can be done by a conventional method such as immersing zeolite in an aqueous solution containing a mineral acid salt such as copper sulfate or copper nitrate or an organic acid salt such as copper acetate. I'll come.

〈Function〉 After adhering the bipedal gel solution to a metal carrier, heating and pressurizing it in a gas phase in a closed container synthesizes zeolite from the gel solution. When it is fired, it becomes a strong zeolite layer.

Since the alumina film is made of acicular alumina,
Facilitates formation of zeolite layer on metal carrier.

The production method of directly synthesizing zeolite onto a metal carrier is
This eliminates the need for a heptaolite wash coating process on the carrier, resulting in a shortening of the catalyst 5A production process.

It is unclear whether or not a catalyst in which Cu is supported on zeolite synthesized directly on a metal carrier tends to exhibit a higher NOxfi+ conversion rate than a conventional Cu/zeolite catalyst, as will be described later.

<Examples> Hereinafter, the present invention will be explained in more detail with reference to Examples.
This example is not intended to equally limit the invention.

Example: Manufacture of a new No. 1 purification catalyst A metal oil with a thickness of 50 cm consisting of 15 cr -5 Al - residual Fe was processed into a corrugated plate, and the corrugated plate was overlapped with a flat plate and wound into a roll shape, with a cell count of 400/ in2. Capacity 1fL (φ1
00XLI:10) is manufactured and press-fitted into the outer cylinder.

This was placed in a vacuum electric furnace and heated and held at a vacuum degree of 10-5 Torr and a temperature of 100°C for 2 hours to perform diffusion bonding between cells and cells and outer cylinder. An alumina film is formed to obtain a metal carrier.

Next, silica sol (: 10wt$ SiO□), sodium aluminate (1,5Na2O/Al2O,), water,
and TPAOH solution [lMo1/i tetrapropylammonium hydroxide: (C3H7)4N+・01l− solution] to a final composition ratio of A120z'60Si02-3N
Mix to obtain a20"2.5TPAOH"400H□O, and stir and mix at room temperature for about 15 minutes to prepare a gel solution.

After immersing the metal carrier in this gel solution and pulling it up, the excess adhering liquid is blown off with air. This is placed in a closed container, saturated steam at a temperature of 160° C. is introduced into the container, and heated at a pressure of 5 kg/cI for 40 hours to crystallize the zeolite on the carrier. After cooling, it was thoroughly washed with water, dried at 100°C for 1 hour, and then heated at 500°C.
C. for 3 hours to form a strong 40 μl thick zeolite layer 3 on the alumina film 2 of the metal carrier 1 as shown in the figure.

The support thus obtained was immersed in a separately prepared 0.02M copper acetate aqueous solution for 30 hours to ion-exchange the Cu, resulting in a Cu/
Obtain a zeolite catalyst.

Comparative example 1. Preparation of Cu/zeolite catalyst by conventional production method A zeolite having the same composition as that of Example 1 is obtained by hydrothermal synthesis of the gel solution used in the above example in a closed container while stirring. The solid matter is removed by suction filtration, thoroughly washed with water, dried at 100°C for 2 hours, and then calcined at 500°C for 3 hours. 55 parts of the powder thus obtained, silica gel (20WL$5iOz) 7[]
parts, 15 parts of water, 15 parts of aluminum nitrate 40Wt2 aqueous solution
A slurry for wash coating is prepared, which is wash coated on the same volume of carrier as in Example 1, dried at 120°C for 1 hour, and calcined at 500°C for 3 hours. Cu is supported by ion exchange in the same manner as in the example to obtain an exhaust gas purifying catalyst.

Comparative Example 2: Production of general-purpose three-way catalyst 100 parts of activated alumina, alumina sol (1OWt$Al
2O,), 50 parts of pure water, and 15 parts of a 40Wt$ aluminum nitrate aqueous solution are mixed and stirred to prepare a slurry for dry coating. This was wash-coated onto the same amount of support as used in Example 1, dried at 120°C for 1 hour, and fired at 700°C for 1 hour to form a γ-alumina coat layer on the support.

After the carrier is subjected to a water-oil treatment, it is sequentially immersed in a dinitrodiamine platinum aqueous solution and a rhodium chloride aqueous solution, dried and calcined, and then immersed in a lanthanum-cerium mixed solution, dried and calcined to obtain carrier 1! ;Pt/Rh per L 1.
570.3 g and La/Ce 0.0310.3■o
A supported catalyst for exhaust gas b and others is obtained.

Performance Test The catalysts obtained in the above Examples and Comparative Examples 1.2 were installed in the exhaust system of a Nibun engine, and their exhaust gas purification performance was investigated. The test conditions were: large gas temperature: 400°C, S
, V, = 60,000h-', A/F = 22te. The results are shown in the table below.

The deceased reported that the NO,e specific activity of the catalyst obtained by directly synthesizing zeolite on a metal carrier was higher than that of a general-purpose three-way catalyst, and was comparable to that of a Cu/zeolite catalyst produced by a conventional method. I understand.

<Effects of the Invention> As described above, according to the present invention, by directly synthesizing zeolite on a metal carrier, a Cu/zeolite catalyst exhibiting particularly high NOx purification performance can be manufactured with high productivity.

The present invention also provides that zeolite can be directly synthesized on a metal carrier, that it is preferable to use a metal carrier on which an alumina film is formed, and that a catalytic metal can be supported on the zeolite layer thus formed. This study is of great significance in that it revealed interesting facts such as increased catalytic activity and provided a new approach to improving catalysts.

[Brief explanation of the drawing]

The figure is a sectional view showing a main part of a metal carrier on which a zeolite layer is formed according to an example. In the figure: 1...Metal carrier 2...Alumina film 3.
...Zeolite layer patent applicant Toyota Motor Corporation

Claims (1)

[Claims] After a gel solution containing raw materials for zeolite synthesis is attached to a metal carrier, it is heated and pressurized in a gas phase in a closed container to form a zeolite layer on the metal carrier, and then a catalytically active metal is applied to it. A method for producing an exhaust gas purifying catalyst characterized by supporting the catalyst.