JPS58177146A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain the titled catalyst having excellent activity even in a low temp. region and durability, by supporting V, Mo and K along with a noble metal by a catalyst carrier. CONSTITUTION:V, Mo and K are supported along with a noble metal by a catalyst carrier to obtain a catalyst wherein the catalytic activity of said noble metal can be enhanced even in a wide range of a temp. region and, as the result, sufficient catalytic activity can be developed even in a low temp. region as well as the durability is made excellent. Because above mentioned beneficial results can be achieved without increasing the support amount of the noble metal, it is advantageous from the point of view of the cost.

Description

[Detailed description of the invention] It is something to do.

Exhaust gas purification catalysts (hereinafter simply referred to as catalysts) are constructed by supporting a noble metal with catalytic activity, such as platinum, rhodium, or palladium, on a ceramic carrier such as alumina. The noble metal absorbs oxygen or hydrogen and activates it, thereby subjecting the exhaust gas to an oxidation/reduction reaction and purifying the exhaust gas.

By the way, internal combustion engines such as automobile engines have a wide temperature range from startup to normal operation. Therefore, i! A catalyst with ambiguous catalytic activity is required regardless of temperature conditions, but catalyst activation is generally accelerated as temperature increases, so in low-temperature ranges such as when the engine is running, the catalyst may not work as effectively. However, there was a risk that incomplete combustion gas would be emitted into the atmosphere.

An object of the present invention is to provide a catalyst that has both excellent activity and durability even in a low temperature range.

In view of this point, the inventors have conducted extensive research and found that
In addition to the usual support metals, i.e. noble metals, vanadium,
If molybdenum and potassium are supported, the catalytic activity of precious metals can be increased even in a wide temperature range.
As a result, it was discovered that sufficient catalytic activity could be exhibited even at low temperatures, and the present invention was constructed based on this finding.

In the present invention, the elements to be supported together with the noble metal, ie, vanadium, molybdenum, and potassium, can be supported on the carrier in the same manner as the method for supporting the noble metal. For example, there is a method in which the above elements are made into water-soluble compounds thereof, a carrier is impregnated with an aqueous solution of the compound, and the carrier is dried and fired. In this case, the compounds used include vanadium, ammonium metavanadate, molybdenum, ammonium molybdate, potassium, potassium carbonate, potassium nitrate, and other compounds containing two types of elements at the same time. , for example, potassium metavanadate, mole molybdate.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 Spherical alumina support 200C with a specific surface area of 50 m”/g
C was impregnated with an aqueous ammonium metavanadate solution, and 1
After drying at 20°C for 2 hours (hereinafter referred to as hr),
It was baked at ℃ x 2 hours. Next, it was impregnated with potassium molybdate aqueous solution, and after drying at 120'Cx 2hr,
It was baked at 0°C for 2 hours. Subsequently, it was impregnated with an aqueous potassium nitrate solution, dried at 120°C for 2 hours, and then dried at 600°C for 2 hours.
It was fired. Next, it is impregnated with rhodium chloride aqueous solution and 1
After drying at 20°C for 2 hours, it was fired at 500°C for 5 hours. Furthermore, it was impregnated with a chloroplatinic acid aqueous solution and heated for 120×2 hr.
After drying, it was calcined at 500°C x O for 5 hours to form a catalyst.
The supported t of each element is shown in the table below.

Comparative Example 1 Specific surface area 50 rr? / g of spherical aluminum carrier 200
Cerium, rhodium and platinum were supported on cc in the same manner as in Example 1, and P! I made it into an i-media. At this time, vanadium, molybdenum, and potassium were not supported.

Comparative Example 2-7 Specific surface area 5 On? / g of spherical alumina carrier 200c
c IC, by carrying cerium, rhodium and platinum scales, vanadium, molybdenum and potassium in the proportion of light distribution,
catalyzed. In this case, a potassium carbonate aqueous solution, an ammonium molybdate aqueous solution and a metavanazine ammonium aqueous solution are used, and the drying after impregnation is carried out at 120'X.
2 hr, 800'C x 2 hr firing of ivy. Also,
Cerium, platinum, and rhodium were supported in the same manner as in Example 1.

table The amount of metal supported indicates the charge per 11 catalysts.

o The supported amount of K was converted to 20. The purification performance of each of the catalysts thus prepared was tested using the following model gas.

Model gas components CO: Q, 8%, NOx: 2,200 ppm, hydrocarbons (C!Hs): 840 pprr), 02
: [L8'li, H2: 0.17%, H,
0: about 5%, CO, zo%, N2; remainder (11 initial (before durability test) activity) 0.8% excess of 02.
A fluctuating gas alternately introduced at 1 Hz to give a 6% excess of CO is heated to 200-350°C (input temperature) and catalyzed at a space velocity (SV) of approximately 60,001-11-1. On the one hand, hydrocarbons (
HC) and Go were oxidized, and NOx was reduced on the other hand, and the conversion rate of HC, (:0 and NOxcDfp) was measured. The measurement results are shown in Figs. 1 to 6.

(After the durability test, the catalyst was exposed for 30 hours to exhaust gas with an active air-fuel ratio of approximately 16. At this time, the -M
The medium bed temperature was approximately 800°C and the space velocity was approximately 60,000 Hr-'. The conditions for measuring the purification rate were the same as those for the initial activity. The measurement results are shown in FIGS. 4 to 6.

As can be seen from the results shown in these figures, the catalyst that supports vanadium, molybdenum, and potassium as components other than precious metals exhibits excellent purification performance both at the initial stage and after durability, and shows particularly high activity at low temperatures. is high, and even after durability, a purification rate of 80% or more can be obtained at a large gas temperature of 300°C.

In this case, the actions of each element are assumed to be as follows: Vanadium: *Along with gold, it can absorb oxygen and hydrogen, and acts as a promoter for noble metals. Therefore, it is possible to improve the catalytic performance of the noble metal that is the catalyst, and to supply oxygen and the like to the noble metal that has been consumed, so that the catalytic activity can be maintained for a longer period of time. This is due to the fact that vanadium changes its valence depending on the surrounding conditions.

Mo11butene: Although the details are unknown, it is said that vanadium (C) makes it easier to change the valence.

Potassium: Suppresses gelatinization of the crystals of the cellulose carrier and stabilizes the carrier.

As described above, since the present invention supports a catalyst having vanadium, molybdenum, and potassium supported together with negative metal paulownia, it is possible to use a catalyst supported only with precious metals, and furthermore, to support at most two of the above elements together with precious metals. Compared to a supported catalyst, the purification performance in the low temperature range (200 to 500°C) is significantly improved. Is this improvement in purification performance of harmful scum? 'Irrespective of knowledge, and regardless of whether or not the durability has been completed, it is recognized. This is also advantageous in terms of cost, as it can be accomplished without the need for a precious metal carrier.

[Brief explanation of the drawing]

Figures 1 to 6 show the input debris 'IM' at the initial stage (before durability).
Graphs showing changes in the purification rate for Nozomi, Figures 4 to 6
The figure shows a graph similar to the above in the case of durability. Figure 1 - Human power (1 degree 1 degree Celsius) yr4p) yr6f! ! 'One person's temperature (℃)

Claims (1)

[Claims] (1) A catalyst for exhaust gas purification characterized by having vanadium, molybdenum, and potassium supported along with precious metals on a catalyst carrier.