Co₃O₄–SiO₂ Nanocomposite: A Very Active Catalyst for CO Oxidation with Unusual Catalytic Behavior

A high surface area Co₃O₄–SiO₂ nanocomposite catalyst has been prepared by use of activated carbon as template. The Co₃O₄–SiO₂ composite, the surface of which is rich in silica and Co(II) species compared with normal Co₃O₄, 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 (H₂O 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 Co₃O₄–SiO₂ catalyst led to the conclusion that adsorption of H₂O 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.