Influence of Preparation Methods of In₂O₃/Al₂O₃ Catalyst on Selective Catalytic Reduction of NO by Propene in the Presence of Oxygen

Selective catalytic reduction of NO with propene was investigated over In₂O₃/Al₂O₃ catalysts prepared by three methods, namely, a single sol-gel (SG), impregnation (IM), and co-precipitation method (CP). The catalysts were characterized by means of BET, XRD, XPS, and TPD. The maximum NO conversion over In₂O₃/Al₂ O₃ prepared by sol-gel method was 95% at 400 °C in the absence of H₂O, and the activity decreased slightly in the presence of H₂O, and it was still 76% even in the presence of H₂O and SO₂. Although the retarding effect of SO₂ on the activity was observed for the three catalysts, In₂O₃/Al₂O₃ (SG) showed relatively high activity. It is found that the high surface area and low average pore diameter are important to the catalytic activity, and the strong interaction between indium and alumina for In₂O₃/Al₂O₃ catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO ⁻₃ and partially oxidized hydrocarbons (RCOO⁻ species) are mainly intermediates, and the oxidation C₃H₆ to RCOO⁻ species maybe the key reaction process in the SCR of NO with C₃H₆.