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

Abstract

A series of Fe_αCu_1−αTiO_x 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 Fe_0.9Cu_0.1Ti 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 Fe_0.9Cu_0.1Ti catalyst are involved in the NH₃-SCR reaction. The adsorption of NO_x is strong in the low temperature range, and large amounts of nitrates were decomposed on the catalyst surface in the high temperature range.