The mechanism of selective NO x reduction by hydrocarbons in excess oxygen on oxide catalysts: VII. The nature of synergism on a mechanical mixture of catalysts

Abstract

Based on a mechanistic study of the selective reduction of NO x by propane on NTK-10-1 and Ni-Cr oxide (NCO) catalysts, the reason for synergism in this process on a mechanical mixture of the catalysts was determined. On the NCO catalyst at temperatures higher than 250°C without NO x activation, C3H8 was oxidized with the formation of a considerable amount of hydrogen. This hydrogen migrated to the surface of NTK-10-1 through a gas phase and reduced this surface. On the reduced surface, H2 reacted with NO x by a mechanism characteristic of supported platinum group metals. In accordance with this mechanism, nitrogen atoms, which were formed by the dissociation of NO on metal atoms reduced by hydrogen, recombined to form nitrogen molecules in a gas phase, whereas oxygen atoms reacted with the hydrocarbon to form CO2 and H2O molecules in a gas phase. The positive effect of H2, which was formed on the NCO surface, on the reduction of NO x on NTK-10-1 is the main reason for synergism. An analysis of the experimental data demonstrated that an effectively working mechanical mixture of catalysts can be obtained if one of the mixture components is responsible for the effective activation of nitrogen oxides and the other is responsible for the activation of hydrocarbons.