Co_3O_4 - SiO_2 Nanocomposite: A very active catalyst for co oxidation with unusual catalytic behavior

摘要

A high surface area Co_3O_4 - SiO_2 nanocomposite catalyst has been prepared by use of activated carbon as template. The Co_3O_4 - SiO_2 composite, the surface of which is rich in silica and Co(II) species compared with normal Co _3O_4, exhibited very high activity for CO oxidation even at a temperature as low as '76 °C. A rather unusual temperature-dependent activity curve, with the lowest conversion at about 80 °C, was observed with a normal feed gas (H_2O content 3 ppm). The U-shape of the activity curve indicates a negative apparent activation energy over a certain temperature range, which has rarely been observed for the heterogeneously catalyzed oxidation of CO. Careful investigation of the catalytic behavior of Co _3O_4 - SiO_2 catalyst led to the conclusion that adsorption of H_2O molecules on the surface of the catalyst caused the unusual behavior. This conclusion was supported by in situ diffuse reflectance Fourier transform infrared (DRIFT) spectroscopic experiments under both normal and dry conditions.