| Direct decomposition of N2O and selective catalytic reduction (SCR) of NO with hydrocarbons or ammonia are the most promising approaches for emission control in environmental catalysis. The recognition of the harmfulness of NO and N2O as well as the stringent federal measure make the catalytic removal of NOx to be a serious challenge in the environmental catalysis. The knowledge of the active sites, intermediates, and reaction pathways are not sufficient to design a catalyst with high activity, selectivity, and durability to poisons such as water and sulfur dioxide. This dissertation investigated the identification of active sites, reactivity of adsorbed NO and N2O species, and reaction pathways for N2 O decomposition and NO SCR with C3H6 and NH 3 over Cu and Fe catalysts.; The adsorption of 5% N2O produced adsorbates of N-bonded N 2O and O-bonded N2O over Cu-ZSM-5. Results of 5% CO and NO competitive adsorption with 5% N2O at 323 K indicate that ion exchanged Cu-ZSM-5 possesses two types of Cu+ sites: one is located at α site on ZSM-5 which is coordinatively unsaturated and adsorbs CO as Cu +(CO)2, NO as Cu+(NO)2 and N 2O as O-bonded N2O; the other type is located at β and γ sites which are less coordinatively unsaturated and attributed to Cu + sites, adsorbs CO as Cu+(CO), NO as Cu+(NO) and N2O as N-bonded N2O. The former Cu+ site is the active site for N2O decomposition and shows higher activity than the latter type.; The C3H6-SCR reaction on Cu-ZSM-5 produced C 3H7-NO2, Cu+-CO, Cu0 -CN, and Cu+-NCO as adsorbed intermediates and CO2, H2O, and N2 as major products. CO2 was produced via Cu+-CO and the difference in CO2 and N 2 formation profiles indicates CO2 and N2 formation followed different reaction pathways. Fe-ZSM-5 presents durability to sulfur and H2O poising for HC-SCR reaction. Addition of H2O and SO2 increased the overall rate of NO conversion at 673, 723 and 773 K via enhancing the formation of Fe2+(NO), while suppressing C3H7COO− and C3H 7NO2− species, thus the formation of CO2 and H2O. It is suggested that CO2 and N2 were produced on different catalytic sites: N2 was produced on Fe2+(NO) sites and CO2 and H2O were produced via C3H7COO− and C3H7NO2− species. The different N2 and CO2 formation pathways suggest that SCR reaction process may be further improved by preparing a catalyst with sites for NO reduction which inhibits CO2 formation without interfering with N2 formation.; Coordinated NH3 at 1620 and 3334 cm−1 on the Lewis acid site of the CuO catalyst was the dominant adsorbate under steady-state NH3-SCR at 573 K, which allows the selective conversion of NH3/NO to N2. The NO reduction rate on zeolite supported copper catalyst is proportional to coverage of ammonia ion (NH4 +) on Bronsted acid of zeolite. |
