Unraveling the Promotional Effect of Co on the Pd/TiO2 Catalyst for H2-SCR of NOx in the Presence of Oxygen

The effect of the introduction of Co to the Pd/TiO2 catalyst for selective catalytic reduction of NOx by H2 (H2-SCR) in the presence of oxygen has been systematically investigated in the present study. The additive Co can not only obviously improve NOx conversion but also enhance N2 selectivity. The added Co induced the formation of Pd0 over the bimetallic PdCo/TiO2 catalyst, which is greatly conducive to the H2-SCR reaction. The spillover of H2 was promoted due to the introduction of Co over PdCo/TiO2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the addition of Co not only contributed to the adsorption and activation of NOx but also led to the generation of NH3 species adsorbed on Lewis acid sites, making the reduction of NOx by the H2-SCR combined with NH3-SCR routes. All of these are responsible for the enhanced catalytic performance of the bimetallic PdCo/TiO2 catalyst. The investigation would provide guidelines for the rational design of a highly active H2-SCR catalyst for the removal of NOx.