Low-temperature NOx reduction with ethanol over Ag/Y: A comparison with Ag/γ-Al2O3 and BaNa/Y

A multistep mechanism has been elucidated for the reduction of NOx in the presence of ethanol over silver-exchanged zeolite Y (Ag/Y). Ethanol reacts with O2 and/or NO2 to form acetaldehyde at temperatures as low as 200 °C. Surface acetate ions, formed from the oxidation of acetaldehyde, react with NO2 to yield nitromethane, a critical intermediate in subsequent deNOx chemistry. CN−, NC−, and NCO− are intermediates likely bound to silver ions. Both CN− and NC− are stable toward reaction under experimental conditions. A significant difference exists between the catalytic activities of Ag/Y and Ag/γ-Al2O3; oxidation of ethanol to acetate at low temperature is significantly faster over Ag/Y than over Ag/γ-Al2O3, and both NO2 and O2 are effective oxidants over Ag/Y. With Ag/Y, pretreatment with either O2 or H2 does not affect the yield of N2, which approaches 60% and remains constant for at least 5 h, making this catalyst promising for NOx reduction.