Poisoning mechanism of different Cd precursors on Fe-Ce/TiO2 catalyst for selective catalytic reduction of NOx with NH3

Abstract

As one of the most harmful heavy metals, Cd can present in many chemical forms in real flue gas and may deactivate the SCR catalysts, but the poisoning mechanism of different Cd species over the Fe-Ce/TiO2 catalysts remains unclear. Therefore, in our work, Fe-Ce/TiO2 catalyst is prepared and doped with Cd(NO3)2, CdCl2, and CdSO4, respectively, aiming to investigate the effect of different Cd precursors on the catalytic performance, physicochemical properties, and poisoning mechanisms of Fe-Ce/TiO2 catalyst. The results demonstrate that different Cd precursors exert different influences on the catalytic activity of the catalyst and the deactivation sequence is CdSO4 <Cd(NO3)2 <CdCl2. The doping of Cd decreases the specific surface area, promotes the grain growth of active species, and results in the aggregation of surface active species to varying degrees. Although the total H2 consumption of Cd poisoned catalysts is enhanced, they are not originated from more amounts of surface active species and thus it does not contribute to the redox cycles and catalytic activity of catalysts. The doping of Cd(NO3)2 decreases the surface acidity of catalysts, while CdCl2 and CdSO4 promote surface acidity, but the adsorbed NH3 over CdCl2 poisoned catalyst is unreactive. In addition, both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms are involved in the SCR reaction over the Fe-Ce/TiO2 catalyst and different Cd poisoning makes no change to the reaction mechanism.