Infrared Study of NO Adsorption and Reduction with C3H6 in the Presence of O2 over CuO/Al2O3

NO, NO/O2, NO2, and NO2/O2 adsorption on CuO/Al2O3 and selective catalytic reduction (SCR) of NO by C3H6 in the presence of 2% O2 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/O2 adsorption at 298–723 K led to rapid formation of Cu2+N and gradual formation of adsorbed (NO−3)2; NO2/O2 adsorption led to immediate formation of (NO−3)2 and gradual formation of Cu2+-OCu2+-O>N–O, Cu2+N–O, and Cu2+N; NO2 adsorption alone did not produce (NO−3)2. Temperature-programmed desorption shows that adsorbed (NO−3)2 decomposed to N2, N2O, and NO at 644 K. Pulsing C3H6 into NO/O2 over CuO/Al2O3 not only removed (NO−3)2 but also reduced Cu2+ to Cu+/Cu0, resulting in the formation of N2, N2O, CO2, and H2O. Steady-state NO/O2/C3H6 reaction on CuO/Al2O3 produced adsorbed C3H7–NO2, CH3COO−, Cu+–NCO, Cu0–CN, and Cu+–CO species, and N2, 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, Cu0–CN, and Cu+–NCO intermediates on Cu0/Cu+ surfaces. This study demonstrates that the pulse and steady-state SCR follows different reaction pathways toward N2 and CO2 products.