Effect of carbon in cobalt-silica-carbon composite catalysts for NO reduction by CO

Cobalt-silica-carbon composites were prepared by sol-gel method and tested as catalysts for NO reduction by CO. Active carbons of different texture parameters were used for synthesis of these composites. A cobalt-silica composite was also prepared for comparison purposes. The catalysts were characterized by low-temperature nitrogen adsorption, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) and tested in NO reduction by CO up to 300 degrees C. Carbon-containing composites were found to exhibit a considerably higher activity in NO reduction by CO than a cobalt-silica catalyst even at low temperatures. A significant difference in transient responses between carbon-containing and carbon-free composition samples was observed revealing different rate controlling steps of the reaction. Carbon presence in cobalt-silica-carbon composites greatly influenced their microstructure including Co3O4 crystalline domain size, surface area, surface composition, and oxidation state, which strongly affected catalyst performance. An increased activity could be due to cobalt sites of different oxidation state with silicon and carbon atoms in their vicinity.