Catalyst for reductive conversion of nitrogen oxides in waste gases

Process comprising reductively converting nitrogen oxides in a gas mixture in the presence of ammonia and oxygen by bringing the gas mixture into contact with a catalyst at 150.degree. to 350.degree. C. with a space velocity of 7,000 to 50,000 h.sup.-1, said catalyst being produced by the process comprising conducting, at least once, the sequence of impregnating a support, containing TiO.sub.2, SiO.sub.2, ZrO, Cr.sub.2 O.sub.3 and/or SnO.sub.2, with a vanadium alkoxide dissolved in an apolar, water-free solvent in an inert atmosphere, and calcining the impregnated support at a temperature of 300.degree. to 600.degree. C. for 3 to 6 hours in the dry gas current with 15 to 25 percent by volume of oxygen to achieve a surface deposit of the active parts in the form of vanadium oxide on the support, said impregnating step and said calcining step being performed in absolutely water-free conditions and environment.