JPS621457A - Preparation of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To prevent the formation of the solid solution of Rh with Al2O3, by adhering a slurry mixture of a TiO2 powder allowed to support a catalytic metal containing Rh and an Al2O3 powder allowed to support a catalytic metal containing no Rh to a carrier before baking. CONSTITUTION:A first catalytic metal containing at least Rh is supported by a TiO2 powder and, separately, a second catalytic metal containing no Rh is supported by an Al2O3 powder. Next, the TiO2 powder supporting the first catalytic metal and the Al2O3 powder supporting the second catalytic metal are mixed to prepare a slurry which is, in turn, adhered to the surface of a catalyst carrier base material. This catalyst carrier base material having the slurry adhered thereto is baked to obtain a catalyst for purifying exhaust gas. As the aforementioned catalytic metals, Rh, Pt, Pd, Ir, Ru, Os, Cr, Ni, V, Cu, Co and Mn can be used alone or in a mixed state of plural metals.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an exhaust gas purifying catalyst used in an internal combustion engine, and more specifically, to a method for manufacturing a catalyst with excellent purification performance and durability. .

[Prior Art] Exhaust gas purifying catalysts for internal combustion engines, particularly automobile engines, are required to have extremely high performance in terms of durability, purification performance, and the like. Car exhaust gas contains carbon monoxide (Go), hydrocarbons (HC), and nitrogen oxides (NO).
x>, etc., and various catalysts are currently being proposed as effective catalysts for simultaneously removing these components. Among them, for example, platinum (Pt), palladium (Pd), or rhodium (R
Catalysts supported with h) and the like, either singly or in combination, are known to have relatively excellent purification performance.

Conventionally, in the production of exhaust gas purification catalysts used in automobile internal combustion engines, etc., first, a monolithic carrier base material made of alumina, cordierite, etc.
Form an alumina support layer. Thereafter, fine particles of the catalyst component are supported on the surface of the alumina particles of the support layer by bringing the support layer into contact with an aqueous solution of the catalyst component, such as chloride, and then dried to obtain a catalyst for exhaust gas purification. Met.

[Problems to be solved by the invention] Among the catalyst metals conventionally used, rhodium
It has excellent reduction performance and is an essential component for 3-way catalysts.

However, rhodium has the property of forming a solid solution with alumina at temperatures above about 700°C. In the conventional production method described above, rhodium is mainly supported on the surface of alumina particles, so rhodium and alumina come into direct contact and form a solid solution due to the heat during calcination or use, which improves catalyst performance. This caused a decline in durability and performance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a manufacturing method for preventing rhodium from becoming a solid solution with alumina and obtaining an exhaust gas purifying catalyst with excellent durability.

[Means for Solving the Problems] In the method for producing an exhaust gas purifying catalyst of the present invention, a first catalyst metal containing at least rhodium is supported on titanium oxide powder, and a second catalyst metal not containing rhodium is supported on alumina powder. a catalyst supporting step in which a slurry is prepared by mixing the titanium oxide powder on which the first catalyst metal is supported and the alumina powder on which the second catalyst metal is supported; It is characterized by comprising an adhesion step of adhering the slurry, and a firing step of firing the catalyst carrier base material to which the slurry is adhered.

The catalyst metals used in the catalyst supporting step include the conventionally known rhodium (Rh), platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Ru),
Precious metals such as osmium (O8>) or chromium (O
r), nickel (N1), vanadium (V), copper (CU
), cobalt (Co) 9, manganese (Mn), and other base metals can be used alone or in combination.

The first catalytic metal may contain a small amount of rhodium, and the components other than rhodium may be any of the above-mentioned catalytic metals.The second catalytic metal may contain no rhodium. Any catalytic metal can be used.

The first catalyst metal is titanium oxide (TiO2) powder,
The second catalyst metals are respectively supported on alumina powder. Here, as a method for supporting, a water-soluble compound of each catalyst metal, for example, rhodium chloride (RhCl3>
, dinitrodiammine platinum [Pt (NH3) t (
Not) t 1, ma! Platinum [Pt (NO3)
t ], platinum chloride M [Ht (Ptcl s )6
t-1zo], palladium nitrate [Pd(NO3)z],
A method can be used in which an aqueous or alcoholic solution of palladium chloride (PdCI2) or the like is used, the solution is brought into contact with each of the above powders by immersion or spraying, and then dried.

In the adhesion step, titanium oxide powder carrying the first catalyst metal and alumina powder carrying the second catalyst metal are mixed to form a slurry. Note that promoters such as rare earth metals and transition metals, alumina powder, etc. can also be added to the slurry. The slurry is then applied to the surface of the catalyst carrier base material by a dipping method or the like. Here, the catalyst carrier base material can be the same as conventional ones, such as a honeycomb-shaped monolith carrier base material or a pellet-shaped carrier base material, and the materials are also the same as before, such as cordierite, mullite,
Alumina, magnesia, spinel, etc. can be used.

In the firing process, the carrier base material to which the above slurry is attached is heated at 70o
This is a step of sintering by heating to a temperature of .degree. C. or higher, and can be carried out in the same manner as conventional methods.

[Operations and Effects of the Invention] In the exhaust gas purifying catalyst obtained by the production method of the present invention, rhodium is supported on the surface of titanium oxide. Therefore, compared to exhaust gas purifying catalysts obtained by conventional manufacturing methods, the portion where rhodium and alumina come into direct contact is extremely small. Furthermore, during firing or use, the formation of a solid solution of rhodium and alumina is significantly less than in the past. As a result, problems such as deterioration of catalyst performance or durability performance hardly occur, and rhodium, which is a scarce resource, can be used effectively.

The manufacturing method of the present invention can efficiently and reliably manufacture such an exhaust gas purifying catalyst.

[Example] (1) Supporting the first catalyst metal Titanium oxide powder 999 with an average particle size of 10 μm was immersed in 100 milliliters of an aqueous solution containing 10 g/liter of rhodium chloride for 1 hour, then pulled out and dried at 200° C. for 1 hour. , Rh-TiOz powder carrying 1% by weight of rhodium was prepared.

(2) Aqueous solution 1000 containing γ-alumina powder 8919 with an average particle diameter of 10 μm and dinitrodiammine platinum 9Q/liter
Pt-A with platinum supported at 1 wt%
12O3 powder was prepared.

(3) Adjustment of slurry, adhesion, 00 g of alumina silua containing 10% by weight of alumina in the calcined ash
and an aqueous solution 150Q containing 40% aluminum nitrate by weight.
and 450 ml of distilled water, and into it, the previously prepared Pt-AlzO3 powder 9000 and Rh-T.
100 g of i1t powder was added and stirred to prepare a slurry paste. In this slurry, a diameter of 10 cm and a length of 15 cm are placed.
The honeycomb-shaped cordierite monolith carrier base material was immersed for 1 minute, pulled up and the slurry inside the cell was blown off with an air stream, dried at 200°C for 1 hour, and then heated at 700°C for 2 hours.
Baked for an hour. This carrier was again immersed in the slurry and the same operation was repeated once again to obtain a catalyst for exhaust gas purification according to the manufacturing method of the example of the present invention. The loading *m of the slurry after firing was 107 o/liter, platinum was supported at 0.9 a/liter, and rhodium was supported at 0.10/liter.

(Conventional Example) Alumina Silua 00Q containing 10% by weight of alumina and milliliter of aluminum nitrate were added, and alumina powder 1000Q was further added and stirred to prepare a slurry.

A monolithic carrier base material made of the same material and having the same shape as that used in the example was immersed in this slurry for 1 minute, and the slurry was blown off in the same manner as in the example, followed by drying at 200°C for 1 hour, and further at 700°C for 2 hours. Baked for an hour. Then, it was dipped into the slurry again and the same operation was repeated to form an alumina support layer. The carrier base material on which the alumina support layer was formed was immersed in distilled water, and after sufficiently absorbing water, it was pulled out and the excess water was blown off, and then immersed in an aqueous solution containing 0.9 q/liter of dinitrodiammine platinum for 1 hour. After removing excess moisture and drying at 200°C for 1 hour, it was immersed in an aqueous solution containing 0.IQ/liter of rhodium chloride and dried in the same manner to remove platinum and rhodium in the same way as the catalyst in the example. A catalyst for exhaust gas purification was obtained by the conventional manufacturing and soaking method.

The two types of catalysts obtained were installed in the exhaust system of a 2-liter engine, and the air/fuel ratio (A/F) was 14°6 and the space velocity (
SV) to 6000Of-(r″″1, catalyst bed temperature 720
A durability test was conducted by operating at ℃ for 300 hours. Thereafter, the HC purification rate was measured at an air/fuel ratio (A/F) of 14.6 by a method of evaluating the temperature characteristics of the purification rate of the catalyst. The results are shown in the figure.

As is clear from the figure, the exhaust gas purification catalyst of the example manufactured by the manufacturing method of the present invention was more durable even after a 300-hour long-term durability test than the exhaust gas purification catalyst manufactured by the conventional manufacturing method. , has excellent purification performance. In addition,
Co and NOx were measured in the same manner, and showed the same tendency as shown in the figure, and the catalyst manufactured by the manufacturing method of the example was clearly superior to the catalyst manufactured by the conventional manufacturing method.

[Brief explanation of the drawing]

The figure is a graph showing the results of evaluating the temperature characteristics of the HC purification rate of the exhaust gas purification catalysts obtained by the manufacturing methods of the example and the conventional example.

Claims (2)

[Claims] (1) A catalyst supporting step in which a first catalyst metal containing at least rhodium is supported on titanium oxide powder and a second catalyst metal not containing rhodium is supported on alumina powder, and the titanium oxide on which the first catalyst metal is supported. powder and the second
An adhesion step in which a slurry is prepared by mixing the alumina powder on which a catalyst metal is supported, and the slurry is adhered to the surface of the catalyst carrier base material, and a firing step in which the catalyst carrier base material to which the slurry is attached is fired. A method for producing an exhaust gas purifying catalyst, characterized in that: (2) The manufacturing method according to claim 1, wherein the first catalyst metal is rhodium and the second catalyst metal is platinum.