Insights into the effect of Cd on simultaneous removal of NOx and dioxins over V2O5-MoO3/TiO2 catalyst: A combination of experimental and DFT study

Abstract

Commercial V2O5-MoO3/TiO2 catalyst has been widely used for synergistic control of NOx and dioxins in organic solid waste (OSW) incineration flue gas due to its excellent catalytic redox performance. However, abundant heavy metals in flue gas are liable to cause catalyst poisoning during operation, leading to severe catalyst lifetime reduction. Therefore, in this study, the poisoning effect of cadmium (Cd), one of the major highly toxic and high-content heavy metals in OSW incineration flue gas, was investigated on the synergistic degradation of NOx and dioxins by V2O5-MoO3/TiO2 catalyst. Combining a series of experimental measures and theoretical calculations, the influences of Cd species on the catalytic activity, physicochemical properties, surface chemical environment, and adsorption behavior of the catalyst were systematically revealed. Results indicated that the negative effect of CdCl2 on NOx and dioxin elimination efficiency was more serious than CdO. It was found that Cd occupied the surface active V = O sites to form Cd-O-V bands, resulting in a lower V5+/(V5++V4+) molar ratio, surface chemisorbed oxygen content, and a suppressed surface oxygen vacancy environment. Density functional theory calculations also verified the adverse effect of Cd species on the surface reactivity of the catalyst, which further weakened the adsorption strength and charge interaction between the reactant and the surface active sites, thus hindering the catalytic performance.