| Abstract
| - The mechanism of the H2-assisted selective catalytic reduction of NO with propane (H2−C3H8 SCR) overAg+-exchanged MFI zeolite (Ag−MFI) was investigated by spectroscopic studies. Transient IR experimentsat 573 K indicate that H2 addition increases the rates of C3H8 oxidation to acetate on Ag−MFI and NOoxidation to the weakly adsorbed NO2. IR spectra obtained during steady-state C3H8 SCR indicate that H2addition increases the coverage of acetate, Ag+−NCO, and Al3+−NCO. The reaction of acetate with NO2yields, via CH3NO2, NCO species, and their hydrolysis yields NH3 as a final precursor of N2. In situ UV−visand EXAFS measurements at 573 K shows that, during the H2 + O2 and H2−C3H8 SCR reactions, Ag+ ionsand partially reduced Ag42+ clusters coexist. ESR spectra obtained after exposing a H2 + O2 gas mixtureshow the formation of superoxide ions. Combined with the results in our previous studies, the followingmechanism is proposed: The Ag42+ cluster and protons formed by H2 reduction of Ag+ ions are involved inthe reductive activation of molecular oxygen into superoxide ion, which should act as an effective oxidantfor C3H8 oxidation to oxygenates such as acetate and NO oxidation to NO2. Thus, H2 addition increases thecoverage of surface intermediates (NCO species) and the gas-phase concentration of NO2 and consequentlyincreases the rate of N2 formation.
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