Method for denitrizing nitrogen oxides contained in waste gas

A method for denitrizing nitrogen oxides contained in a waste gas which contains arsenic compounds therein in amounts of about 0.01-1.0 ppm, which comprises putting the waste gas into contact with a catalyst essentially consisting of:

• (a) titanium,
• (b) arsenic in amounts of about 0.01-35 parts by weight in terms of weight as As.sub.2 O.sub.3 in relation to 100 parts by weight of titanium in terms of weight as TiO.sub.2, and
• (c) at least one base metal selected from the group consisting of W and Mo, in amounts of 0.05-80 parts by weight in terms of weight as WO.sub.3 and MoO.sub.3, in relation to 100 parts by weight of titanium as TiO.sub.2, in the presence of a reducing gas at elevated temperatures, thereby to reduce the nitrogen oxides.