Abstract: A catalyst for removal of nitrogen oxides which shows extremely good catalytic activity and is excellent in durability and is low in the activity of oxidizing SO.sub.2 into SO.sub.3 be prepared at a low cost by impregnating a titanium oxide carrier with a vanadium sulfate, a vanadyl sulfate or a mixture thereof and then reacting a mixed gas consisting of 0.05 to 100% by mole of ammonia and 99.95 to 0% by mole of an inert gas which is inert to both ammonia and vanadium and vanadyl sulfates with the impregnated carrier while the reaction mixture is maintained at a temperature of 300.degree. to 520.degree. C., and preferably 370.degree. to 450.degree. C., or by shaping a mixture of titanium oxide and a vanadium sulfate, a vanadyl sulfate or a mixture thereof into a desired shape and then reacting a mixed gas consisting of 0.05 to 100% by mole of ammonia and 99.

Abstract: Catalyst for removing nitrogen oxides, whose activity is lowered by poisoning with sulfur oxides, is contacted with an ammonia gas at a temperature of 200.degree. to 500.degree. C, whereby the sulfur oxides are liberated from the catalyst, and the catalyst is regenerated.Concentration of the ammonia gas to be used in the regeneration treatment must be at least 1% by volume and preferably 5 to 50% by volume of ammonia is used in a mixture with other inert diluting gas. The regenerated catalyst is given an activity as high as that before the poisoning without bringing about any damage and cracking to the catalyst.