Infrared study of NO adsorption and reduction with C3H6 in the presence of O2 over CuO/Al2O3

NO, NO/O-2, NO2, and NO2/O-2 adsorption on CuO/Al2O3 and selective catalytic reduction (SCR) of NO by C3H6 in the presence of 2% O-2 were investigated by infrared spectroscopy coupled with mass spectroscopy to provide insight into the mechanism of NO adsorption and reduction. Adsorption studies show that NO/O-2 adsorption at 298-723 K led to rapid formation of Cu2+<(O)(O)>N and gradual formation of adsorbed (NO3-)(2); NO2/O-2 adsorption led to immediate formation of (NO3-)(2) and gradual formation of (Cu2+-O)(Cu2+-O)>N-O, Cu2+<(O)(O)>N-O, and Cu2+<(O)(O)>N; NO2 adsorption alone did not produce (NO3)(2). Temperature-programmed desorption shows that adsorbed (NO3-)(2) decomposed to N-2, N2O, and NO at 644 K. Pulsing C3H6 into NO/O-2 over CuO/Al2O3 not only removed (NO3-)(2) but also reduced Cu2+ to Cu+/Cu-0, resulting in the formation of N-2, N2O, CO2, and H2O. Steady-state NO/O-2/C3H6 reaction on CuO/Al2O3 produced adsorbed C3H7-NO2, CH3COO-, Cu+-NCO, Cu-0-CN, and Cu+-CO species, and N-2, CO2, and H2O as products. Dynamic behavior of adsorbates under transient conditions suggests that the steady-state SCR reaction may proceed via adsorbed C3H7-NO2, Cu-0-CN, and Cu+-NCO intermediates on Cu-0/Cu+ surfaces. This study demonstrates that the pulse and steady-state SCR follows different reaction pathways toward N-2 and CO2 products. (C) 2000 Academic Press.