Reduction of nitric oxide by isobutene over Cu-Mn alloys

Cu-Mn alloys with various bulk compositions have been used in the catalytic reduction of NO by i-C4H8 at 500 degrees C. The gas-phase reactions were m onitored by mass spectroscopy (MS) and the catalyst surfaces were character ized by X-ray photoelectron spectroscopy (XPS) at certain stages of the rea ctions. The compositions and oxidation states of the alloy surfaces are str ongly dependent on the bulk composition and the oxygen pressure, and eventu ally influence the reaction kinetics, product distribution, as well as mech anism of NO reduction. On a Cu-Mn (atomic 8%) alloy surface, with a medium oxygen pressure (reducing conditions), the reaction of NO with partially ox idized products of i-C4H8 is suggested to be the main mechanism of NO reduc tion. However, too low or too high an oxygen pressure leads to direct decom position of NO with the production of N-2 or N2O, depending an reducing or oxidizing reaction conditions. On high-manganese-concentration alloy surfac es (55%, 92% atomic), under strong reducing conditions, the main path of NO reduction is via the reaction of adsorbed NO2 with i-C4H8, which gives ris e to N-2 production. When the reaction conditions pass from reducing to oxi dizing, NO decomposition leads to the formation of N2O. (C) 1999 Academic P ress.