Selective removal of NO2 in the presence of oxygen and NO over Pd/SiO2 catalysts

Catalytic reduction of NO2 in the presence of excess oxygen and NO has been studied over a 0.2% Pd/SiO2 catalyst between 120 and 260 °C. CO is effective in selective reduction of NO2 at temperatures below 180 °C. Temperature programmed desorption (TPD) and FT-IR studies have been used to investigate the adsorption sites during the reaction conditions. A Langmuir–Hinshelwood mechanism involving oxidised Pd sites is proposed for the reduction of NO2 with CO, where both reactants adsorb competitively on Pd2+ sites. Cl deactivates the catalyst for the reduction of NO2 with CO. This problem can be overcome by using propylene as a co-reductant. Furthermore, addition of propylene widens the temperature window of operation.