Enhancing the low temperature NH3-SCR activity of FeTiO x catalysts via Cu doping: a combination of experimental and theoretical study.

Abstract

A series of FeαCu1−αTiOx catalysts with variable Cu doping amounts was directly synthesized by the sol–gel method and their catalytic performances were tested for the selective catalytic reduction of NO with ammonia. The highest activity was achieved on Fe0.9Cu0.1Ti catalyst. NO conversion was above 80% and N2 selectivity exceeded 90% on this catalyst in the temperature range of 200–375 °C. High NO and NH3 oxidation activities facilitated the high NH3-SCR activities of the catalysts in the low temperature range, while too strong NH3 oxidation ability resulted in the decline of NH3-SCR activity. DFT calculations based on the Fe and Cu co-doping TiO2 model showed that the barrier of NH3 activation is dramatically reduced as compared to pure Fe doping. This is due to the lowered p-band of lattice O. However, such activated O will also strongly decrease the barrier for the dissociation of NH2 to NH species, which will lead to the formation of N2O. Both Brønsted and Lewis acid sites over Fe0.9Cu0.1Ti catalyst are involved in the NH3-SCR reaction. The adsorption of NOx is strong in the low temperature range, and large amounts of nitrates were decomposed on the catalyst surface in the high temperature range.