Siemens Aktiengesellschaft

Doris Vogel

Helmut Schmelz

Josef Sprehe

Dietmar Hein

Norbert Landgraf

Wolfgang Gajewski

A Catalyst for reducing the nitrogen oxides in flue gases by a reducing agent and a catalytically active composition are described. The catalyst increases resistance to catalyst poisons such as arsenic trioxide. The composition contains 60-90% by weight of titanium, 10-30% by weight of molybdenum, and 0.2-10% by weight of vanadium, as their respective oxides. A very pure titanium dioxide having less than 500 ppm of calcium and less than 100 ppm of iron, being 60% in the anastase modification. It has a mean particle size of 10 to 100 nm, a mean pore radius of 10 to 30 nm and a BET surface of 10 to 80 m.sup.2 per gram. The catalyst is prepared by wet-grinding a suspension of the titanium dioxide with the vanadium pentoxide and molybdenum trioxide in stated proportions. The suspension is then dried and precalcined for several hours at 450.degree. to 550.degree. C. The precalcined material is comminuted to diameters smaller than 180 .mu.m. The pulverized material is then mixed with water and coated onto a metal substrate, dried and then calcined for several hours at 450.degree. to 550.degree. C.

Catalyst for reducing nitrogen oxides

A catalyst for reducing the nitrogen oxides in flue gases by a reducing agent and a catalytically active composition is described. The catalyst increases resistance to catalyst poisons such as arsenic trioxide. The composition contains 60-90% by weight of titanium, 10-30% by weight of molybdenum, and 0-10% by weight of vanadium, as their respective oxides. A very pure titanium dioxide having less than 500 ppm of calcium and less than 100 ppm of iron, and being 60% in the anastase modification. It has a mean particle size of 10 to 100 nm, a mean pore radius of 10 to 30 nm and a BET surface of 10 to 80 m.sup.2 per gram. The catalyst is prepared by wet-grinding a suspension of the titanium dioxide with the vanadium pentoxide and molybdenum trioxide mill in stated proportions. The suspension is then dried, and precalcined for several hours at 450.degree. to 550.degree. C. The precalcined material is comminuted to smaller than 180 .mu.m. The pulverized material is then mixed with water and coated on to metal substrate, dried and then calcined for several hours at 450.degree. to 550.degree. C.

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Erlangen, Germany

Doris Vogel