A novel application of trapping catalysts for the selective low-temperature oxidation of NH3 to N2 in simulated biogas

The low-temperature selective oxidation of NH3 to N-2 in simulated biogas containing a large excess of CO and H-2 has been examined using a novel NH3 and a standard NOx trapping catalyst. The N-2 selectivity during NH3 oxidation at 200 degrees C for a 1%Pt-20%BaO-Al2O3 NOx trapping material, with typical lean/rich switches, was initially good (>90%) but decreased markedly over a small number of cycles. In contrast, the N-2 yield obtained using a novel NH3 trapping material (1%Pt-20%CuO-Al2O3) with rich/lean fuel switching exceeded 95% and was stable over many switching cycles, while an unmodified 1%Pt-Al2O3 catalyst displayed poor N-2 selectivity under all conditions. The data obtained from probe reactions between the various potential adsorbates and gaseous species of the reaction indicate that the N-2 yields obtained from the 1% Pt-20% CuO-Al2O3 catalyst are formed via an Internal Selective Catalytic Reduction (iSCR) between NHx species adsorbed on the trapping component and NO formed from NH3 total oxidation on the Pt during the lean cycle of operation. For the 1%Pt-20%BaO-Al2O3 catalyst, NOx, formed during lean operation, is reduced to N-2 in the rich cycle by a combination of reactions with NH3, CO, and H-2. The use of a hybrid catalyst, based upon a combination of iSCR and NOx trapping processes, gave a peak N-2 yield of >95% and an integrated N-2 production over the entire rich/lean cycle of 75%. These results reflect the potentially dramatic improvements possible by rational design of catalyst systems based upon a fundamental knowledge of the processes involved. (C) 2000 Academic Press.