Selective catalytic reduction catalysts

This patent describes a process for removing NO/sub x/ from a gas containing excess oxygen which involves adding NH/sub 3/ to the gas and passing the gas over a catalyst at a temperature of 3500 to 4500C to react the NO/sub x/ with the NH/sub 3/. The improvement uses as the catalyst, a catalyst consisting essentially of an oxysulfur compound of manganese or nickel, or mixtures, carried by a mixture of ceria and alumina on a support. The ceria comprises 2-60% by weight of the mixture of ceria and alumina and the manganese, nickel or mixture thereof comprises from 0.1-25% by weight of metal based on the carrier weight