Low temperature NO_x and N₂O reduction by H₂: mechanism and development of new nano-catalysts

Abstract

The understanding of the mechanistic aspects and development of new catalysts for NO_x reduction is a priority area of research. Precious metal substituted TiO₂ (Ti_0.99M_0.01O_2-δ, where M = Ru, Rh, Pd, Pt) catalysts have been synthesized and investigated for the catalytic reduction of NO by H₂. These catalysts have higher activity compared to other catalysts reported in literature. The rate of NO reduction by H₂ depends on the reducibility of the catalysts. Temperature programmed reduction experiments with H₂ indicate that as the H₂ dissociation temperature decreases (reflecting the reducibility of the catalysts), the rate of NO + H₂ reaction increases. A new bi-functional reaction mechanism has been developed that accounts for NO adsorption on Mⁿ⁺ and NO dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. Consistent with the experimental results, it was found that NO reduction rate was dependent on the adsorption and dissociation of H₂ on the metal.