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

A highly active Pd supported on TiO 2 coating on a SiO 2 nanosphere (Pd/SiO 2 –TiO 2 (C)) catalyst has been developed for the selective catalytic reduction of NO x by H 2 (H 2 –SCR). The coating structure of TiO 2 on the SiO 2 nanosphere exerts an important effect on the catalytic performance of the catalyst. This Pd/SiO 2 –TiO 2 (C) catalyst shows superior activity with 93.2% NO x conversion at 150 °C, and high tolerance to CO and H 2 O, which is significantly outperformed Pd supported on TiO 2 particle (Pd/TiO 2 ) catalyst. Compared with Pd/TiO 2, Pd/SiO 2 –TiO 2 (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 NO x, NH 3, and NH 4 + species formed on Pd/SiO 2 –TiO 2 (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 H 2 –SCR catalyst for the removal of NO x .