Selective Catalytic Reduction of Nitric Oxide with Hydrogen over Pd Based Catalysts

摘要

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/TiO_2/Al_2O_3 as the catalyst and at temperatures ranging from 140°C to 180°C. The addition of V_2O_5 to this catalyst not only increases the NO conversion, but also widens the reaction temperature window to 250°C. The effects of CO, O_2 and H_2 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 H_2 and -0.18 with respect to CO. Increasing the O_2 concentration from 2% to 10% gave only a slight decrease in NO conversion. FTIR studies showed that a significant amount of NH_4~+ was formed over the V_2O_5-containing catalyst, during the reaction, at temperatures > 200°C, as compared to almost no NH_4~+ formation over the V_2O_5-free sample. The higher activity of 1%Pd-5%V_2O_5/TiO_2-Al_2O_3 is partly attributed to the in-situ formation of NH_4~+.