Selective catalytic reduction of nitrogen oxides (NOx) in combustion effluents utilizes ammonium carbamate to achieve the advantages of ammonia as an NOx-reducing agent, while improving ease and safety of transportation, and economy of operation. The carbamate (11) can be transported dry or in aqueous solution in a sealed container (10) and water (12) is passed through the container to make up the solution prior to introduction to an SCR reactor (18). The convenience of urea is achieved without the need for hydrolysis of the urea or the problems of catalytic fouling which might occur if that were not accomplished.
