Selective catalytic reduction of nitric oxide with hydrogen over Pd-based catalysts

Catalytic reduction of NO with hydrogen in the presence of excess oxygen was studied using Pd-based catalysts. High steady-state conversion of NO (>80%) is achieved, using 1%Pd/TiO₂/Al₂O₃ as the catalyst and at temperatures ranging from 140 to 180 °C. The addition of V₂O₅ to this catalyst not only increases NO conversion, but also widens the reaction temperature window to 250 °C. The effects of CO, O₂, and H₂ concentrations on the NO conversion were also investigated. It was found that the reaction order is nearly first order with respect to NO, 0.6 with respect to H₂ and -0.18 with respect to CO. Increasing the O₂ concentration from 2 to 10% produced only a slight decrease in NO conversion. FTIR studies showed that a significant amount of NH4+ was formed over the V₂O₅-containing catalyst, during the reaction, at temperatures >200 °C, compared with almost no NH4+ formation over the V₂O₅-free sample. The higher activity of 1%Pd-5%V₂O₅/TiO₂-Al ₂O₃ is partly attributed to the in situ formation of NH4+.