Deactivation Effects Of Alkali Metal On A CeMoTiO_x Catalyst For The Selective Catalytic Reduction Of NO_x With NH₃

Ce-based oxides,with excellent oxygen storage capacity and redox ability,show a certain potential application as NH3-SCR catalysts.A new CeMoTiOx catalyst was prepared by simple homogeneous precipitation method,showing excellent NH3-SCR performance in wide temperature range.With the extensive application of biomass fuel in industry,the toxic effect of alkali metal on NH3-SCR catalyst in DeNOx process has attracted more and more attention.Since the previous research mainly explored the mechanism of alkali metal poisoning of traditional V2O5-WO3(MoO3)/TiO2 catalyst and few was carried out over Ce-based catalysts,it is very important to explore the deactivation effects of potassium on CeMoTiO.x catalyst.This paper took CeMoTiOx catalyst with high NH3-SCR performance as research object,and carried out experiments on CeMoTiOx.and 0.3%K/CeMoTiOx based on previous work.In addition,the steady-state kinetic model based on our previous work is obtained to study the deactivation mechanism of alkali metal on CeMoTiOx.In this dissertation,the suppression effects of potassium on CeMoTiOx for the selective catalytic reaction of NOx with NH3 were investigated by characterization and kinetic methods.CeMoTiOx catalyst exhibited high SCR activity and high N2 selectivity during SCR reaction.After being poisoned by potassium,the SCR activity and N2 selectivity of 0.3%K/CeMoTiOx decreased in the whole temperature range.However,the SCR activity of the poisoned CeMoTiOx could be substantially regenerated by water washing method.The H2-TPR test showed that potassium induces an inhibition on the reduction capacity of CeMoTiOx,which is associated with the lower SCR activity of 0.3%K/CeMoTiOx.The separated NO oxidation results indicated that potassium suppresses the oxidation of NO to NO2,which can result in the inhibition of low-temperature SCR activity over CeMoTiOx.The separated NH3 oxidation results showed that potassium promotes the oxidation of NH3 to NOx and N2O,which could lead to a decrease of N2 selectivity over CeMoTiOx.Meanwhile,TPD and in situ DRIFTS results indicated that 0.3%K/CeMoTiOx has lower NOx and NH3 adsorption capabilities,which should be an important reason for the inhibitory effects on NH3-SCR activity.In addition,the kinetic method results demonstrated that potassium has a great inhibitory effect on SCR reaction rates in the whole temperature range,while potassium enhances both NSCR and C-O reaction rates in the high temperature region.According to the steady-state kinetic model,the alkali metal reduced adsorption capacity of NH3 and NOx and reduction of surface Ce4+ over CeMoTiOx catalyst,which results in the reduction of kSCR-LH and KSCR-ER reaction kinetics by LangrNuir-Hinshelwood mechanism and Eley-Rideal mechanism.At the same time,the alkali metal promoted the NH3 oxidation to NOx and N2O,which increases the KNSCR reaction kinetic,and then promotes the NSCR and C-O reaction rate.