Reasonable design of Sm-modified Cu-based catalyst for NH3-SCO: Role of the amide intermediates

Abstract

The selective catalytic oxidation of ammonia (NH3-SCO) is currently the most effective method used to eliminate NH3. However, one of the major challenges for NH3-SCO is the development of catalyst capable of completely converting NH3 into harmless N2 and water vapor. In this paper, a high N2 selective catalyst prepared by the sol-gel method using TiO2 as the support, Cu as the active species, and Sm as the auxiliary agent is presented. Compared to traditional Cu/TiO2 catalyst, the 4SmCu/TiO2 catalyst has higher catalytic activity and N2 selectivity at low temperatures. The NH3 conversion can reach 100%, and the selectivity of N2 can be maintained at 100% at 275 °C. The excellent catalytic activity is attributed to the highly dispersed active species, abundant Lewis acid sites (LASs), and the generation of large amounts of surface-adsorbed oxygen. In addition, doping Sm species will cause TiO2 lattice distortion, and at the same time load the distorted TiO2 with more active material. Moreover, in-situ DRIFTS analysis suggests that both the 4SmCu/TiO2 and Cu/TiO2 catalysts follow the "internal" selective catalytic reduction (iSCR) mechanism during NH3-SCO reactions. The 4SmCu/TiO2 catalyst generates more amides (-NH2), which reduces the non-selective oxidation of the catalysts and promotes the formation of N2. This provides a new idea and method for the selective catalytic oxidation of NH3 to N2 and water vapor using Cu-based catalysts.