JPH02169033A - Catalyst for combustion - Google Patents

Abstract

PURPOSE:To obtain a catalyst for combustion preventing the deterioration of activity and separation of noble metal particles from the carrier and having stable performance over a long period of of time of incorporating noble metal particles into the crystal lattice of a perovskite type multiple oxide and firmly fixing them. CONSTITUTION:A perovskite type multiple oxide is formed on an inorg. carrier such as silica or alumina with a first metal such as Ba, La or Sr, a second metal such as Co, Ni or Cr and a noble metal such as Pt or Pd. Since particles of the noble metal having catalytic activity are incorporated into the perovskite type multiple oxide as a constituent and fixed in the crystal lattice of the oxide, the separation of the particles from the carrier is prevented even under severe conditions including high temp. and the resulting catalyst maintains high catalytic activity over a long period of time.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a catalyst for combustion of various fuels, and more particularly, the present invention relates to a catalyst for combustion of various fuels. This invention relates to a combustion catalyst used to combust vaporized liquid fuel such as gas or alcohol.

(Prior art and its problems) Precious metal catalysts in which various noble metals such as platinum and palladium are supported on inorganic carriers have been widely used as fuel catalysts (for example, Japanese Patent Laid-Open No. 63-65951). .

Noble metal particles, which are catalytically active substances in conventional combustion catalysts, are supported singly on an inorganic carrier. Usually platinum,
Particles of noble metals such as palladium and rhodium alone have poor heat resistance, and when a combustion reaction occurs on a combustion catalyst supporting the noble metal particles by supplying and receiving oxygen, the noble metal particles are repeatedly adsorbed and desorbed. Sintering occurs and deteriorates, or the noble metal particles are exposed to high temperatures and volatilize or aggregate with each other, resulting in a decrease in activity. Even when the noble metal particles are bonded to each other with a weak bonding force on the carrier by forming an alloy or the like with other particles, the noble metal particles similarly deteriorate, shortening the life of the catalyst and increasing the cost. This causes deactivation or loss of precious metals.

In order to overcome this drawback, efforts are being made to develop methods for firmly adsorbing metal particles onto a carrier in the form of a single metal, but there is a limit to increasing the bond strength between noble metals and inorganic carriers. Even if it is possible to extend the catalyst life to some extent, the current situation is that this has not led to a dramatic increase in catalyst life.

(Object of the Invention) In order to eliminate the above-mentioned drawbacks, the present invention provides a combustion device in which noble metal particles are firmly bonded onto a carrier and are not easily desorbed and can maintain high catalytic activity over a long period of time. The purpose is to provide a catalyst.

(Means for Solving the Problems) The present invention provides a combustion catalyst comprising an inorganic carrier coated with an active oxide in which noble metal catalyst particles are dispersedly supported as a catalyst component, in which the noble metal catalyst particles include barium. , lanthanum, strontium, neodymium and cerium, and at least one second metal selected from the group consisting of cobalt, nickel, iron, chromium and molybdenum to form a perovskite. This is a combustion catalyst characterized by forming a type composite oxide.

The present invention will be explained in detail below.

In the present invention, departing from the conventional concept of catalyst production in which noble metal particles themselves are adsorbed onto a carrier, the noble metal particles having catalytic activity are incorporated into a composite oxide, that is, a perovskite type composite oxide, as a component thereof, and the composite It is characterized by being fixed in the crystal lattice of the oxide so that it will not be detached from the carrier even under harsh conditions such as high temperatures, and this structure dramatically extends the life of the catalyst. It allows you to improve. Furthermore, the perovskite-type composite oxide has an oxygen storage effect,
This reduces the proportion of the noble metal particles that come into direct contact with oxygen, making it possible to more effectively suppress the deterioration.

The noble metal used in the present invention is not particularly limited as long as it can form a perovskite-type composite oxide together with the first and second metals described below, and any platinum metal such as platinum, palladium, rhodium, and ruthenium may be used. Can be done.

Further, the inorganic carrier is not particularly limited, and conventionally used inorganic carriers such as alumina, silica, zirconia, titania, alumina-silica, alumina-zirconia, and zirconia-silica can be used without restriction.

The first and second metals that form the perovskite-type composite oxide together with the noble metal particles are appropriately selected from the group consisting of barium, lanthanum, strontium, neodymium, and cerium, and the group consisting of cobalt, nickel, iron, chromium, and molybdenum. selected.

The perovskite type composite oxide usually has the chemical formula RMX
, R and M represent the first or second metal, and X represents oxygen. In order to prepare the perovskite-type composite oxide, for example, a mixed solution of nitrates of each metal containing the noble metal is formed, the solution is coated on a carrier, and the coated carrier is heat-treated to dissolve the nitrates of each metal. A desired combustion catalyst may be obtained by converting it into a metal oxide and forming a perovskite-type composite oxide on the carrier.

In the combustion catalyst prepared in this way, the noble metal particles, which are the catalytically active metal, are firmly fixed in the perovskite crystal structure, and do not desorb or deteriorate even under extremely harsh conditions, and can last for a long period of time. It becomes possible to provide a catalyst that can burn fuel with high activity over a period of time.

(Examples) Examples of the present invention will be described below, but these examples do not limit the present invention.

Example 1 5% lanthanum oxide and 5% lanthanum oxide on mullite carrier
The activated alumina is then coated with a mixed solution of neodymium nitrate, strontium nitrate, cobalt nitrate, and palladium nitrate (molar ratio 1:
1:1:1) and then dried for 80 minutes.
A perovskite-type composite oxide of palladium was formed on the activated alumina by heat treatment at 0° C., and a combustion catalyst was obtained.

A catalytic combustion reaction of methane was carried out using 40 g of the catalyst under normal pressure.
When the test was carried out under the conditions of an air flow rate of 801/min, a flow rate of log gas entering the catalyst of 10 m/sec, and a combustion temperature of 1300°C, the catalyst of this example gave clean combustion gas of 1300°C in 200 hours.

Comparative Example 1 A mullite carrier was coated with activated alumina, and then the activated alumina was immersed in an aqueous palladium nitrate solution, dried, and heat-treated at 800° C. in a hydrogen stream to obtain a combustion catalyst. When this catalyst was used in a methane combustion reaction under the same conditions as in Example 1, the catalyst of this comparative example became unable to ignite after 20 hours.

Example 2 A perovskite-type composite oxide containing platinum was formed on activated alumina under the same conditions as in Example 1, except that a dinitrodiammine platinum nitric acid aqueous solution was used in place of palladium nitrate, and a combustion catalyst was prepared.

When a catalytic combustion reaction of propane was carried out using 40 g of the catalyst under the same conditions as in Example 1, clean combustion gas at 1300° C. was provided for 200 hours.

Comparative Example 2 A platinum-containing catalyst was obtained under the same conditions as Comparative Example 1, except that a dinitrodiammine platinum nitric acid aqueous solution was used instead of the palladium nitrate aqueous solution, and the treatment was performed in the atmosphere instead of in a hydrogen stream. When the catalyst was used for propane combustion under the same conditions as Comparative Example 1, the catalyst of this Comparative Example became unable to ignite after 20 hours.

Example 3 A perovskite-type composite oxide containing rhodium was formed on activated alumina under the same conditions as in Example 1, except that rhodium nitrate was used instead of palladium nitrate, and a combustion catalyst was prepared.

Example 1: Catalytic combustion reaction of methane using 40 g of the catalyst
When conducted under the same conditions as above, clean combustion gas at 1300° C. was provided for 200 hours.

Comparative Example 3 A rhodium-containing catalyst was obtained under the same conditions as Comparative Example 1 except that an aqueous rhodium nitrate solution was used instead of an aqueous palladium nitrate solution, and this catalyst was used for methane combustion under the same conditions as Comparative Example 1. The catalyst in the example failed to ignite after 20 hours.

(Effects of the Invention) The combustion catalyst according to the present invention departs from the conventional idea of supporting noble metal catalyst particles on a carrier as they are, and incorporates the noble metal catalyst particles into the crystal lattice of a perovskite-type composite oxide. By firmly fixing the particles, deterioration and detachment of the particles can be effectively prevented, and a combustion catalyst having stable catalytic performance over a long period of time can be provided.

In other words, in normal combustion reactions, adsorption and desorption of oxygen on the carrier surface occur very frequently, and in conventional combustion catalysts, the noble metal catalyst particles with catalytic activity are not firmly fixed on the carrier, so the oxygen The noble metal particles may be detached from the support along with the detachment of the noble metal particles, or the catalyst may be damaged by adsorbed oxygen, resulting in a decrease in catalytic activity, or the noble metal particles may aggregate with each other, leading to an underactive state.

On the other hand, in the combustion catalyst according to the present invention, since the noble metal catalyst particles having catalytic activity are incorporated into the crystal lattice of the perovskite composite oxide, the noble metal catalyst particles are removed from the carrier unless the crystal lattice is destroyed. Since it does not desorb and has strong bonds with adjacent atoms such as oxygen in the lattice, it is hardly affected by adsorbed oxygen, further improving the stability of the precious metal catalyst particles. It becomes possible to maintain the existing catalytic activity for a long period of time.

Claims (2)

[Claims] (1) A combustion catalyst comprising an inorganic carrier coated with an active oxide having noble metal catalyst particles dispersed thereon as a catalyst component, wherein the noble metal catalyst particles include barium, lanthanum,
Perovskite-type complex oxidation with at least one first metal selected from the group consisting of strontium, neodymium, and cerium and at least one second metal selected from the group consisting of cobalt, nickel, iron, chromium, and molybdenum. A combustion catalyst characterized by forming a substance. (2) The combustion catalyst according to claim 1, wherein the noble metal catalyst particles are at least one selected from palladium, platinum, and rhodium.