Influence of different preparation methods on the activity of Ce and Mo co-doped ZSM-5 catalysts for the selective catalytic reduction of NOx by NH3.

Abstract

The Ce-doped different MoO3 [conventional molybdenum oxide (con-MoO3) or nano molybdenum oxide (nano-MoO3) and synthetic molybdenum oxide (syn-MoO3)] modification of ZSM-5 catalyst synthesized by different preparation methods (the combination of grinding and ion-exchange method and the combination of impregnation and ion-exchange method) was studied on selective catalytic reduction (SCR) of NOx with NH3. The results demonstrated that the SCR performance of the prepared Ce-doped syn-MoO3 modification of ZSM-5 catalyst [Ce(0.9%)-syn-MoO3(6%)/ZSM-5] by the combination of impregnation and ion-exchange method was better than Ce-doped con-MoO3 modification of ZSM-5 [Ce(0.9%)-con-MoO3(6%)/ZSM-5] and Ce-doped nano-MoO3 modification of ZSM-5 [Ce(0.9%)-nano-MoO3(6%)/ZSM-5] via the combination of grinding and ion-exchange method, especially when the temperature window is 200-350°C. That is because it is easy to form Mo-O-Al by the smaller sized MoO3 more easily interacting well with Brønsted acid under calcining temperature, which results in the decrease of Brønsted acid sites in the catalyst. Combing with the binding energy of Mo for all the catalysts, the combination of Mo and Al (Mo-O-Al) altered the chemical environment around the Mo species. Furthermore, Ce(0.9%)-syn-MoO3(6%)/ZSM-5 exhibited excellent sulfur resistance.