JPS6034741A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain titled catalyst inexpensively having high activity and wide range of application by supporting superfine particles of metal, alloy or compound obtd. by gaseous phase chemical reaction between vapor contg. metallic halide and reducing gas on ceramic carrier of catalyst. CONSTITUTION:Superfine particles having <=1,000Angstrom particle size are obtd. stably by gaseous phase chemical reaction of halide wherein vapor contg. at least one kind of metallic halide such as halide of Fe, Co, or Ni, etc. is introduced together with reducing gas such as H2 with different introducing speed to each other causing laminar contact with each other. Superfine particles prepd. in this way are supported by the ceramic carrier. Obtd. catalyst is inexpensive and has high catalytic activity, maintains performance stably for long time use and is applicable to wide range of conditions sufficient as three component catalyst for the purification of exhaust gas of automobile.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an exhaust gas purification device for removing nitrogen oxides, hydrocarbons, and carbon oxides contained in large amounts in the exhaust gas generated during the combustion process of gasoline, etc. in an automobile engine. Regarding catalysts.

Automobile exhaust gas has been widely discussed in society as one of the sources of pollution, and ever since its regulation has been viewed as a problem, research and development has been progressing on both engine improvements and exhaust gas purification catalysts.

As a result, great results have been achieved in terms of purification using catalysts, and exhaust gas purification using catalysts is currently being carried out for ordinary passenger cars. However, although these catalysts are expensive and resource-constrained, there are no concerns about secondary pollution and there are no excellent substitutes for these catalysts as they have high activity. is mainly used. In particular, three-way catalysts, which are expected to become mainstream in the future, use precious metals such as rhodium or ruthenium, which are considered to be a major resource problem, in addition to platinum, and it is difficult to recover and recatalyze used catalysts. Research is also attracting attention.

Nitrogen oxides, which are harmful substances in automobile exhaust gas (
NOx), hydrocarbons (HC) and -carbon oxides (Co)
The concentration of fuel varies significantly depending on the state of fuel combustion within the engine (air-fuel ratio = air A/fuel F). Below the engine's stoichiometric air-fuel ratio (A/F = 14.65), HC and CO show a reverse behavior in which they increase while NOx decreases in accordance with the tendency for oxygen shortage. The currently commonly used three-way catalyst is NO.
The region where x, HC, and CO can be efficiently purified at the same time is limited to a very narrow range of the air-fuel ratio around the stoichiometric air-fuel ratio. However, studies are also being conducted on controlling engine operation in order to keep the exhaust gas within this range. On the other hand, diesel engine cars, which have become rapidly popular in recent years due to their excellent fuel efficiency, have a problem in that the exhaust gas is rich in oxygen, making it extremely difficult to purify NOx using catalysts. There is. Therefore, efforts are being made to develop a catalyst for NOx purification that exhibits excellent properties even in an oxygen-rich state.

In other words, the present invention is a catalyst that uses base metal elements that are relatively inexpensive and abundant in resources, has high activity and catalytic ability, and is particularly applicable as a three-way catalyst for exhaust gas purification in a wide range of conditions. The purpose is to provide Type 1 or Type 2
Ultrafine particles of metals, alloys, compounds, or mixtures thereof obtained by a gas phase chemical reaction of vapor containing one or more metal halides and a reducing gas, preferably ultrafine particles having a diameter of 100OX or less, are used as a catalyst to support crosstalk. The catalyst is supported on a ceramic catalyst carrier such as γ-alumina or titania using a method such as the following method.

With recent technological advances, it has become possible to produce ultrafine particles with a diameter of less than 1,000 people, and these ultrafine particles have, for example, high purity, small particle size, large specific surface area, high surface tension, and low internal pressure. It is attracting attention for its performance, which is different from ordinary powders, such as being extremely stable even in the atmosphere. The present inventors have investigated and investigated how these unique properties function as catalytic abilities.

The methods for producing ultrafine particles include physical methods such as gas evaporation method and plasma evaporation method, chemical methods such as gas reduction method and gas phase reaction method, and physicochemical methods such as active hydrogen-molten metal reaction method. There is. Among these methods, the in-gas evaporation method is attracting attention as a method in which particle size can be easily controlled and high purity metal particles of 1000^ or less can be stably obtained. This method involves vaporizing metals at high temperatures under low pressure conditions using an inert gas, and then condensing the metals in the form of ultrafine particles through collisions with gas atoms and molecules. There are disadvantages in that productivity is quite low and it is expensive, and it is difficult to produce ultrafine particles of high melting point metal.

Therefore, from the standpoint of catalyst production, this method has the disadvantage of high production costs and is considered to lack generality.

On the other hand, the halide vapor phase chemical reaction method, which is one of the chemical methods, has been basically known for a long time, but it has difficulties in controlling the particle size and has problems such as not being able to obtain homogeneous ultrafine particles. There was a problem. Ultrafine particles of less than 1000 Å are stabilized by a recently developed special method, i.e., a halide vapor phase chemical reaction method in which a metal halide vapor flow with a velocity difference and a reducing gas flow such as hydrogen are brought into contact in a layered manner in the same direction. I was able to obtain the desired result. This method makes it possible to control the formation of an alloy, its composition, and even its particle morphology, and also solves most of the difficulties in uniformity of particle size and removal of impurity substances.

Furthermore, since this method allows continuous operation and has very high productivity, it is fully possible to keep the production cost of a catalyst using the obtained ultrafine particles low.

Ceramics such as γ-alumina and titania are produced by cross-wire method using base metals such as iron, cobalt, and nickel, which are aggregates of ultrafine particles produced by such a metal halide vapor phase chemical reaction method, and fine alloy particles. The catalyst, which is cross-wired with catalyst carrier powder, pellet-formed, and heat-treated, has high activity and catalytic ability, maintains stable performance over long periods of use, and has sufficient characteristics as a three-way catalyst for automobile exhaust gas purification. It was shown that This catalyst using ultrafine particles shows high activity against NoX even in the extremely low co concentration range of 2% or less, and is suitable as a catalyst for purifying exhaust gas from diesel engines. It was confirmed.

In the present invention, the exhaust gas purifying catalyst prepared by supporting various ultrafine particle catalysts and a ceramic catalyst carrier may be mixed according to a conventional method, and may be of a pellet type or a mata honeycomb type. Finer particles of ceramics are also effective as catalyst carriers.

The base metal-based ultrafine particles used in the present invention are mainly iron-based base metal substances such as iron, nickel, and cobalt, but the halide vapor phase chemical reaction method is not limited to single metal ultrafine particles, but also alloy ultrafine particles. It is also possible to produce ultrafine compound particles by combining reaction gases. Therefore, in the present invention, the use of any of these ultrafine particles alone is far from using them in combination at a fixed ratio. It is also possible to mix these with conventional base metal powders or noble metal powders.

As described above, the present invention uses various types of ultrafine particles produced by a metal halide vapor phase chemical reaction method, which is one of the methods for chemically producing ultrafine particles, or a mixture of them in a certain proportion as a catalyst. The catalyst is supported on a ceramic catalyst carrier such as γ-alumina or chikunia, and is cheaper and more practical than conventional catalysts. Because of this, it not only has high activity and high catalytic performance comparable to precious metal catalysts, and excellent exhaust gas purification ability, but also exhibits stable performance even during long-term use, and has no secondary pollution. It is possible to provide an exhaust gas purifying catalyst that has favorable effects such as being worry-free.

Catalysts manufactured using various ultrafine powders of the present invention as catalyst supports are particularly suitable for purifying automobile exhaust gas, but they can also be used satisfactorily for general industrial purposes, exhaust gas purification, and even general chemical purposes. be.

Next, an example will be described.

Example Nickel 25 produced by halide gas phase chemical reaction method
%, cobalt 10%, and iron balance ultrafine particles were used. The particle size of the ultrafine particles was approximately 300 to 500 mm.

This nickel-cobalt-iron alloy fine powder and γ-alumina as a carrier with a particle size of 1 to 3 μm are uniformly mixed in a ball mill, and a fatty acid is further added and mixed uniformly. After drying, It was molded into pellets of mm x 6M.

Next, the pellets were heat-treated in nitrogen gas at a temperature of about 800° C. for several hours to vaporize the fatty acids and produce an exhaust gas purifying catalyst.

FIG. 1 shows the results of investigating the air-fuel ratio (A/F) and NO conversion rate for this catalyst. For comparison, the results are also shown for a mixed powder of the same composition of iron, cobalt and nickel with a normal particle size of 70 to 100 μm.

Curve a in the figure is a graph obtained by measuring a catalyst produced using ultrafine alloy particles under reaction conditions of 600°C. It is a graph measured under reaction conditions. Note that the space velocity was 30,000/hour when the catalyst amount was 25 tons (inner alloy ultrafine particles 20% by weight). The same conditions were applied to the case of ordinary mixed powder.

As is clear from curve a of the obtained graph, the catalyst using ultrafine alloy particles not only showed a high conversion rate of 98% or more for No, but also a high air-fuel ratio (A/F ) showed high activity even in a wide range of regions.

Such properties are not only comparable to noble metal catalysts such as platinum, but also indicate the possibility of further improving the properties depending on the target by appropriately combining base metal ultrafine particles. Of course, as is clear from the curve, such favorable properties cannot be expected from ordinary base metal powders.

In addition, in the purification gas used in this example, No.
FIG. 2 shows the concentrations of CO and He expressed in terms of air-fuel ratio (A/F). That is, when read in conjunction with FIG. 1, it can be seen that NO was effectively converted even at considerably low CO and HC concentrations.

[Brief explanation of the drawing]

Figure 1 is a graph comparing the effects of the catalyst in Examples of the present invention and a catalyst using normal particle size powder of the same composition.
The figure is a graph showing the concentration of the purifying gas used in this example.

Claims (1)

[Claims] Particle size 1000 obtained by gas phase chemical reaction of vapor containing one or more metal halides and reducing gas
^Using ultrafine particles of metals, alloys or compounds,
A catalyst for exhaust gas purification characterized by supporting this on a ceramic catalyst carrier.