Method and catalyst for reducing pollutants in gases

Details Method and catalyst for reducing pollutants in gases Method and catalyst for reducing pollutants in gases

1997-12-22

2001-01-02

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S168000, C422S171000, C502S071000, C502S077000, C502S078000, C502S325000

Utility Patent

active

06168764

ABSTRACT:

BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Application No. 196 53 910.2, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a catalyst for reducing pollutants in gases.
It is known from DE 44 45 945 C1 to use catalysts for reducing nitrogen oxides, said catalysts containing two materials. The reduction of the nitrogen oxides takes place in the presence of hydrocarbons (HC) as reducing agents. The two materials however have a low catalytic effect as far as nitrogen oxides are concerned. A first material, namely titanium mordenite, acts adsorptively with respect to the HCs, while the second material, composed of metal oxides, acts adsorptively toward the nitrogen oxides. In a catalyst prepared from these materials, there is an up to 50% reduction of nitrogen oxides in the range between 200° C. and 450° C.
The goal of the invention is to provide a novel method and a corresponding novel catalyst whose advantages are comparable to those known from DE 44 45 945 C1.
The goal is achieved according to the invention by a method and catalyst that adsorbs hydrocarbons as a reducing agent and decreases nitrogen oxides.
A mixture of two materials is proposed for the catalyst according to the invention, with the first material, referred to hereinbelow as the adsorption material, having an adsorbent effect on the additional substance, and with the second material, hereinafter called the oxidation material, having an oxidizing effect on the pollutant.
When two materials that preferably have a slightly active effect catalytically as far as the pollutant is concerned are used as the adsorption material and the oxidation material, it is surprising that good catalytic reduction of at least one pollutant nevertheless takes place preferably in a gas containing oxygen.
Hydrocarbons are preferably used as the additional substance. Preferably nitrogen oxides are removed as the pollutants, which are at least temporarily oxidized with the aid of the oxidizing material to form NO
2
. Possibly, the NO
2
is then converted to nitrogen (N
2
) and additional substances with the aid of hydrocarbon that is released by the adsorption material and/or not absorbed by the absorption material.
H-zeolites are preferably used as the adsorption material, H-ZSM5 or H-mordenite for example. Metal oxides are preferably used as the oxidation materials, with the term “metal oxides” also covering mixed metal oxides, for example spinels, especially the metal oxide Al
2
O
3
and the like and/or perovskites in accordance with the present patent application.
Further logical embodiments of the invention can be found in the subclaims. Moreover, the invention will now be described in greater detail with reference to examples. In the figures, graphs have been provided for the various examples, with the concentration of NO
x
and/or CO
2
and/or propene (C
3
H
6
) being plotted as a function of temperature (in ° C.).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.


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WPI Abstract, JP 7096195 A, Seiji Harufuji et al., Nov. 4, 1995.

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