Method for simultaneously abating nitric oxides and nitrous oxides in gases containing them

The invention concerns a method for purifying flue gases before they are released into the atmosphere of their nitrogen oxides N₂O and NO_x by reaction with ammonia by causing them to circulate at temperatures between 200 and 600 C. on a catalyst based on beta-zeolite loaded with iron. The invention is particularly useful for treating tail gases from factories producing nitric acid.