Commercially viable processes of the SCR type for converting nitrogen oxides to nitrogen with ammonia: (a) in the presence of an iron, cobalt, nickel, or other transition metal sulfate with Bronsted activity; (b) at a temperature of not more than 250° C.; and (c) preferably in a dry environment if room or near room temperatures are employed. The process may be used to eliminate nitrogen oxides from flue gases, other exhaust gases, and the like and in other applications in which the reduction of a nitrogen oxide is wanted. Excess ammonia and/or sulfur dioxide may be maintained in the reaction mixture to promote process efficiency. The catalysts have appreciable Bronsted activity even at ambient temperatures and are capable of effecting NO x conversions with efficiencies of at least 50 percent in even demanding applications at temperatures below the 250° C. maximum. They can be unsupported or supported on a porous support. If of the latter type, the catalyst can be prepared by impregnating the support with an aqueous solution of a selected transition metal salt and then drying the impregnated support. Also, if the salt is not a sulfate, the salt is calcined and the resulting oxide reacted with a compound such as sulfur dioxide to generate the sulfate.

J. Edward Cichanowicz

Papers

Low temperature catalytic reduction of nitrogen oxides