NOx Reduction with added oxygenates: Mechanism and the role of NO as a reductant

This presentation will focus on the selective reduction of NOx with added oxygenates over BaNa/Y and Ag/Y zeolites and Ag/γ-Al2O3. This chemistry involves a complex set of coupled reactions with a number of common crucial intermediates. In these reactions, over the indicated catalysts, acetaldehyde, which can be directly introduced or formed via oxidation of ethanol, is oxidized to form acetate ions. The acetate ions react with NO2 to form nitromethane which decomposes to HNCO via a dintiromethane intermediate. HNCO can then be hydrolyzed to give NH3 which can react with HONO to form ammonium nitrite, which can then efficiently decompose to N2 and H2O at low temperatures. Since nitric acid is also present, surface nitrates and ammonium nitrate can form. Data will be presented to show that NO acts as a reductant of nitrate ions, ammonium nitrate and nitric acid, converting less desirable species to the more volatile nitrite analogs. When nitromethane is directly introduced to a NOx stream over Ag/Y∼100% conversion of NOx to N2 is achieved at temperatures as low as 140 °C. This result coupled with data on the reactivity of surface acetate provides insights into the rate limiting step in deNOx chemistry in these systems.