Selective catalytic reduction of NO x by hydrogen over modified Pd/TiO2-Al2O3 catalyst under lean-burn conditions

A series of Ni, Sn and Ca modified Pd/TiO₂-Al₂O₃ catalysts were prepared by the incipient wetness impregnation method and their catalytic performance for the selective catalytic reduction of NO _x by H₂ was evaluated. The results showed that the NO _x conversion and N₂ selectivity were improved over Pd-Sn/TiO₂-Al₂O₃ and Pd-Ni/TiO₂-Al₂O₃ catalysts above 200 °C. More importantly, the N₂ selectivity and high-temperature activity of Pd-Sn/TiO₂-Al₂O₃ catalyst was far superior to the single Pd/TiO₂-Al₂O₃ catalyst. The optimal Sn loading was 2 wt.%. X-ray diffraction (XRD) results showed that the interaction between Pd and Sn promotes the dispersion of Pd over TiO₂-Al₂O₃. Temperature-programmed reduction (H₂-TPR) results demonstrated that the addition of Sn contributes to the formation of Pd⁰ and improving the redox property of Pd/TiO₂-Al₂O₃. The additives of Ni and Sn also facilitated the absorption of NO _x and the oxidation of NO to NO₂, which play important roles in the selective catalytic reduction of NO _x by hydrogen.