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°C to 180°C. The addition of V₂O₅ to this catalyst not only increases the 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 1st-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% gave only a slight decrease in NO conversion. FTIR studies showed that a significant amount of NH₄⁺ was formed over the V ₂O₅-containing catalyst, during the reaction, at temperatures > 200°C, as compared to almost no NH₄⁺ formation over the V₂O₅-free sample. The higher activity of l%Pd-5%V₂O₅/TiO₂-Al₂O₃ is partly attributed to the in-situ formation of NH₄⁺.