Superior catalytic performance within H2O-vapor of W-modified CoMn2O4/TiO2 catalyst for selective catalytic reduction of NOx with NH3

Abstract

Improving the resistance to H2O is crucial to promote industrial applications of Mn-based catalysts for selective catalytic reduction of NOx by NH3 (NH3-SCR). In this work, we reported the CoMn2O4/TiO2 catalyst, and W was introduced as a promoter to enhance the resistance to H2O at low-temperature. CoMn2O4/W-TiO2 catalyst exhibited remarkable H2O-resistance of above 95% NOx conversion and nearly 100% N2 selectivity at 150–250 °C in the presence of 10 vol% H2O. Further, the role of tungsten and the effect of water on the structure and chemical properties of CoMn2O4/W-TiO2 catalyst were revealed by various techniques of BET, XRD, Raman, H2-TPR, NH3-TPD, XPS and in-situ DRIFTS experiments. The superior performance was attributed to unique spinel structure, mesoporous structure, highly dispersed tungsten species, greater surface acidity. The electron cycle among Mn, Co, W and Ti was beneficial to maintain the Mn3+/Mn4+ and Co3+ at high concentrations and enhance lattice oxygen mobility. The SCR reaction mainly followed the Eley-Rideal (E-R) mechanism over two catalysts, but the poor water resistance of CoMn2O4/TiO2 was attributed to the suppression of NH3 activation and E-R mechanism, despite NH3 adsorption was enhanced. Both Lewis and Brønsted acid sites were created by the incorporation of tungsten in the presence of H2O, and enhanced NH3 adsorption, promoting E-R reaction pathway. Besides, N2 selectivity was significantly enhanced by H2O, which could be due to a decrease in the redox activity of both catalysts. This study opens up a new avenue for designing efficient and environment-friendly NH3-SCR catalysts and looks promising for practical application.