TiO2 Coating on SiO2 Nanosphere Supported Pd Catalyst for the H2–SCR of NOx in the Presence of Oxygen

A highly active Pd supported on TiO2 coating on a SiO2 nanosphere (Pd/SiO2–TiO2(C)) catalyst has been developed for the selective catalytic reduction of NOx by H2 (H2–SCR). The coating structure of TiO2 on the SiO2 nanosphere exerts an important effect on the catalytic performance of the catalyst. This Pd/SiO2–TiO2(C) catalyst shows superior activity with 93.2% NOx conversion at 150 °C, and high tolerance to CO and H2O, which is significantly outperformed Pd supported on TiO2 particle (Pd/TiO2) catalyst. Compared with Pd/TiO2, Pd/SiO2–TiO2(C) has higher Pd dispersion and smaller Pd particle size, more surface chemisorbed oxygen, and metallic Pd species, all of which contributed to the improved performance. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) reveals that more reactive NOx, NH3, and NH4+ species formed on Pd/SiO2–TiO2(C), and the CO poisoning is mainly due to the slight inhibition of the formation of these reactive species. This research provides a promising strategy to design a superior H2–SCR catalyst for the removal of NOx.