Low-temperature CO oxidation over Ag/SiO2 catalysts

Ag/SiO2 catalysts for CO oxidation were prepared by an incipient wetness impregnation method, and characterized by XRD and TEM. The effects of Ag loading and the different pre-treatments with O2/H2 on the crystallite structure of silver catalysts and the activity of CO oxidation over Ag/SiO2 were also studied. It was found that w(Ag)=8% Ag/SiO2 catalyst pretreated with oxygen at 500 ℃ exhibited better catalytic performance (T98=65 ℃), and the activity was further increased after following hydrogen treatment at 200 ℃. However, the activity decreased when the treatment temperature increased to 300 ℃. Crystallite Ag and Ag2O species were observed from XRD after oxygen pretreatment at 500 ℃, and the following hydrogen treatment at 50-200 ℃ led to the reduction of the Ag2O species and the dispersion of crystallite silver. However, prolonged hydrogen treatment at high temperatures (>200 ℃) induced the aggregation of silver particles, which may be one of reason resulting in the decrease of the activity for CO oxidation. It could therefore be concluded that nano-crystallite silver with certain particle sizes would be favor of the low-temperature CO oxidation.