A kinetic study on reduction of nitric oxide over cobalt tetraphenylporphyrin supported on titanium dioxide

Abstract

The catalytic reduction and decomposition of nitric oxide and nitrous oxide over cobalt tetraphenylporphyrin supported on TiO 2 (Co-TPP/TiO 2) were investigated kinetically and mechanistically in the reaction temperature range of 50 to 150 °C, and reveal a high catalytic activity brought about by supporting on titanium dioxide. The kinetic equation for the reduction of nitric oxide with hydrogen over Co-TPP/TiO 2 ( V = k × P NO −0.9 P H 2 0.6) suggested that the surface reaction between nitric oxide adsorbed strongly on the cobalt ion and hydrogen adsorbed dissociatively on the porphyrin ring is the rate-determining step. The selective formation of nitrous oxide in the initial stage of the reaction and its successive transformation to molecular nitrogen were explained in terms of the stronger adsorption of nitric oxide. Decomposition of nitric oxide and nitrous oxide also proceeded over this catalyst, producing nitrous oxide and molecular nitrogen, respectively. The residual oxygen produced on Co-TPP may be transferred to the support to a certain limit. The characteristic activity of (Co-TPP/TiO 2) can be ascribed to the drastic modification in the electronic configuration of the cobalt ion, as well as the porphyrin ring, induced by the electron transfer from the support.