Enhanced Catalytic Activity of Cobalt Tetraphenylporphyrin on Titanium Dioxide by Evacuation at Elevated Temperatures for Intensifying the Complex-Support Interaction

Article abstract of DOI:10.1021/j100232a015

Remarkable catalytic activity of cobalt tetraphenylporphyrin (CoTPP) supported on TiO2 was found to be developed by the evacuation of the catalyst at 200 deg C for the reduction and decomposition reactions of nitric oxide which were observed with a circulating reactor.The reduction reaction was detectable to as low as 50 deg C, and the conversion of nitric oxide into nitrogen was completed at 100 deg C within 4 and 1 h with hydrogen and carbon monoxide, respectively.The decomposition of nitric oxide into nitrous oxide without any reductant was also observable at 100 deg C.Such an activity increase of roughly 20 times due to the evacuation was related to the increased capacity for the adsorption of hydrogen and the further activation of carbon monoxide and nitric oxide.These enhancements can be ascribed to the pronounced electron transfer from the support to the complex (to produce active Co^2-δ and anion radical which can be active sites for carbon monoxide and nitric oxide, and hydrogen, respectively) strengthened by the partial dehydration of the support which may produce on its surface the coordinatively unsaturated titanium ion surrounded by an appropriate number of TiOH groups.A spillover mechanism is proposed in the decomposition of nitric oxide where oxygen produced probably on the central metal ion of the complex can be transferred to the support.