Siemens Aktiengesellschaft

Gunther Spitznagel

Erich Hums

Peter Heinz Fischer

Ronald Neufert

Klaus Huttenhofer

An SCR catalyst containing titanium, molybdenum and vanadium has the particular characteristic that its catalytic activity is significantly less than that of a tungsten-containing catalyst. That disadvantage has been compensated for in the past by using a comparatively large volume of catalyst. In contrast to the conventional practice of using a molybdenum oxide proportion of about 10 to 12% by weight, the invention proposes that the molybdenum proportion of the catalyst, in the form of molybdenum trioxide MoO.sub.3, is about 0.01 to 5% by weight, preferably 1.5 to 4% by weight, relative to the weight of the catalyst mass. A catalyst containing this amount of molybdenum thus has an activity comparable to that of a tungsten-containing catalyst. The invention is applicable to all deNO.sub.x catalytic converters which call for the simultaneous presence of a reducing agent, in particular plate-type and honeycomb-type catalytic converters.

Catalyst for reducing the nitrogen oxide concentration in a flowing

In an arsenic resistant mixed oxide catalyst and a process for producing the same, oxides of at least the metals vanadium and molybdenum are provided, especially for reducing nitrogen oxides in flue gases in the presence of a reducing agent such as ammonia and carbon monoxide. A MoO.sub.3 phase and at least one oxygen-rich mixed oxide phase such as V.sub.9 Mo.sub.6 O.sub.40 is at least partly converted into a mixed oxide phase being poorer in oxygen such as a V.sub.9 Mo.sub.4 O.sub.25 phase, for increasing arsenic resistance.

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Erlangen, Germany

Gunther Spitznagel