Low-temperature CO oxidation over Au/ZnO/SiO2 catalysts: Some mechanism insights

We report a new type of supported Au catalyst active in low-temperature CO oxidation. Au/ZnO/SiO2 catalysts were prepared by routine deposition–precipitation with ammonium hydroxide (Au/ZnO/SiO2-NH3) and aqueous solution of Na2CO3 (Au/ZnO/SiO2-Na2CO3) as the precipitation agent. The catalysts were characterized by BET surface area, X-ray diffraction, transmission electron microscopy, X-ray photoemission spectroscopy, photoluminescence spectroscopy, and X-ray absorption spectroscopy. Au/ZnO/SiO2-Na2CO3 is more active than Au/ZnO/SiO2-NH3, achieving a complete CO conversion at 303 K. The structures of Au nanoparticles and ZnO are strongly affected by the Au–ZnO interaction in Au/ZnO/SiO2 catalysts. The Au–ZnO interaction is stronger, and thus the Au nanoparticles are more highly dispersed in Au/ZnO/SiO2-Na2CO3 than in Au/ZnO/SiO2-NH3. Our results suggest that CO oxidation catalyzed by supported Au nanoparticles follows different mechanisms at low and high reaction temperatures and that a weakly chemisorbed species is involved in low-temperature CO oxidation.