Study On The Surface Interaction And Catalytic Performance Of Supported Catalysts For NO Elimination

Part ?:Supported metal oxide catalysts are widely used in industrial and academic research.The investigation of the surface interaction between active components and promoter or support is significant to understand the nature of catalytic reactions and development the effective and practical catalysts.During my PhD period,the main research is involving in a series of multicomponent supported catalysts for catalyric reduction of NO.Usually,there are two essential factors to affect the surface interaction between catalyst components,i.e.,the intrinsic feature of active component(dispersion behavior,electrical structure)and the surface properties of support(redox,textural property).Tuning the surface interaction between active component and support is one of important strategies to improve catalytic properties.In this dissertation,firstly,excess CO was employed to simulate reducing rich-burn exhaust environment and the effect of CO-pretreatment on the supported binary metal oxide(CuO-VOx/?-Al2O3)in NO+CO reaction was investigated.Experiment results showed that CO-pretreatment led to significant enhancement on the catalytic performance for some of the catalysts.In addition,the enhancement caused by CO-pretreatment for CuO-VOx/y-Al2O3 was much more remarkable than that of single-metal supported catalyst(CuO/?-Al2O3,VOx/?-Al2O3)and mechanical mixture of them.Both of the un-pretreated and pretreated samples were characterized in detail.It could be inferred from the results that Cu2+-O-V5+species on the surface of unpretreat catalyst CuO-VOx/?-Al2O3 was reduced to Cu+-?-V4+(? represents oxygen vacancy)by CO-pretreatment,which was beneficial to the adsorption of CO and dissociation of NO.Distinguishing from ordinary surface oxygen vacancy(e.g.,Cu+-?-Cu+),Cu+-?-V4+was considered as surface synergetic oxygen vacancy(SSOV)for the synergistic effect between the vacancy and two different adjacent metal ions.The SSOV was assumed to be crucial for the remarkable promotion of catalytic activities in NO+CO reaction.Part ?:Based on the investigation of the Part I,bimetallic supported catalyst CuO-VOx/y-Al2O3 were prepared by co-impregnation and sequential impregnation methods and were investigated for NO reduction by CO to uncover the dependence of activities on surface species.It was found that the activities of the catalysts were highly dependent on the impregnation sequence.Catalytic activity of the catalysts showed increasement after CO pretreatment.Moreover,co-impregnation catalyst provided greater improvement after CO-pretreatment than their step impregnation counterparts.Comparing the activity results dependence with the characterization results of XRD,H2-TPR,BET,UV-Vis and XPS techniques,it was indicated that the dispersion of Cu and V was affected by impregnation methods.There are strong interactions between Cu and V in the CuV/Al catalyst prepared by co-impregnation to form Cu2+-O-V5+ species.This interactions in sequential impregnation catalysts,Dy contrast,are weaker because one surface component might by covered by the subsequence and weaken the adsorption of CO and NO.Moreover,it was linked to that co-impregnation is more conducive to the formation of Cu+-?-V4+(SSOV)during CO-pretreatment than sequential impregnation methods,which could greatly facilitate the NO+CO reaction.Part ?:Ceria-based solid solutions were synthesized and used as supports to prepare MnOx/Ce0.8Ti0.2O2 and MnOx/Ce0.8Sn0.2O2 catalysts(Mn/CeTi and Mn/CeSn)for low temperature selective catalytic reduction of NO by NH3.The effects of Ti or Sn doping on the catalytic performance of MnOx/CeO2 catalyst were investigated.Experimental results show that doping of Ti or Sn increases the NO removal efficiency of MnOx/CeO2.The NO conversion of Mn/CeTi catalyst is more than 90%at temperature window of 175?300? under a gas hour space velocity of 60,000 mL·g-1·h-1.Modified catalysts are also found to exhibit greatly improved resistance to sulfur-poisoning.Characterization results indicate that doping of Ti or Sn brings about catalysts with higher BET surface area,enhanced oxygen storage capacity and increased surface acidity.X-ray photoelectron spectroscopy(XPS)analysis of spent catalysts following SCR reaction in the presence of SO2 verify that the loss of surface Mn species was inhibited by doping of Ti,which contributes to extend the sulfur durability.The SCR activity is considered as well to be promoted by the dual redox cycles in Mn/CeTi(Mn4++Ce3+(?)Mn3++ Ce4+,Ce4++Ti3+(?)Ce3++ Ti4+)and Mn/CeSn(Mn4++Ce3+(?)Mn3++Ce4+,2Ce4++Sn2+(?)2Ce3++Sn4+)catalysts.