| CO oxidation and water-gas shift(WGS)reaction have important value of application in eliminating residual CO from environment and industrial process.As for CO oxidation reaction,the source of remarkable performance of supported gold catalysts have long been an attractive issue for researchers.However,as the extreme complexity of catalytic enviroment,plenty of fundemental issues stemed from catalysis process are still under debate.Therefore,comparable systems were selected and the combination of ex-situ and in-situ characterizations were employed to track the active site and the entire reaction process accurately.Thus,the structure-function relationship were revealed and the origin of the catalytic behavior were better understand.As for WGS reaction,the reaction mechanism,which is the theoretical foundations for the design and synthesis of efficient catalysts,have been explored in-depth by researchers.However,the efficient synthesis of highly active catalysts are still inadequate.Therefore,both inert and redox carrier supported catalysts with high-performance were synthesized by reasonable control.Then the effect of catalyst structure on the reaction behavior was revealed and the reaction mechanism were deepen understanding.Thereby the effective exploration and guidance were made for optimization of efficient catalyst in WGS reaction.The main work of this thesis is as follows:(1)Exploring the active sites in CO oxidation reaction:the effect of gold state on reactivity of CO oxidation reaction over Au/TiO2 catalystsThe supported gold catalyst shows excellent catalytic activity for CO oxidation and has great application prospects.Therefore,the study of active site in this reaction is of great significance.Here,catalysts with either metallic or positively charged gold were separately prepared by deposition-precipitation method with the same TiO2 nanotube.The catalytic behavior of these two catalysts were observed in the CO oxidation reaction.For the initially inactive Aun+/TiO2(1<n<3)catalyst,Aun+ was gradually reduced by CO to Au0 during the reaction from in-situ DRIFTS measurement.The change of gold state enhanced the CO adsorption capacity and further improved the catalytic performance.In addition,in-situ Raman results proved that the transition from Aun+ to Au0 might be helpful to generate oxygen vacancies in TiO2,which was beneficial to the activation of O2.Therefore,we pointed out that Au0 was more active than Ann+ in catalytic CO oxidation at room temperature.(2)Investigating the effects of reactants adsorption and products desorption on the performance of CO oxidation reaction:the effect of reactants adsorption and products desorption for Au/TiO2 in catalyzing CO oxidationSubsequently,in this thesis,the subject was investigated by loading gold onto different crystal planes of TiO2.The CO oxidation reactivity of Au/TiO2-101 is much higher than Au/TiO2-001(9.33×10-3 molCOgAu-1S-1 vs.6.23×10-4 molCOgAu-1S-1 at 30?).Only gold particles with 2 nm in diameter were detected in Au/TiO2-101,while not only gold particles(?4 nm)but also gold clusters(?1.3 nm)were existed in Au/TiO2-001.The difference in gold species resulted in different CO adsorption that CO was more effectively adsorbed on the surface of Au/TiO2-101 due to the more Au0 sites.Meanwhile,the bidentate carbonates which could hinder the reactive sites were more tightly adsorbed on TiO2-001.However,bicarbonate was the main surface species of TiO2-101,which was more easily decomposed into carbon dioxide.Therefore,the differences between Au/TiO2-101 and Au/TiO2-001 in effective CO adsorption and CO2 desorption resulted in differences in reactivity.Hence,we revealed that the CO oxidation reactivity was greatly influenced by the behavior of surface species adsorption and desorption(3)Construction of high-efficiency inert carrier supported catalyst for WGS reaction preparation of Cu/MgO catalyst and its structure-function relationship in WGS reactionGenerally,the ability to activate water of inert supports is limited due to the lack of oxygen vacancies,thereby performing lower reactivity in WGS reactions.However the inert support,whether the metal oxides which can react with water or the hydroxides with hydroxyl groups on the surface has not been studied in WGS reaction.Therefore,highly active Cu/MgO catalyst was successfully prepared by the deposition-precipitation method.Structural characterization confirmed that MgO and Mg(OH)2 were coexisted during the reaction because of the presence of water in the reaction gas Based on TPSR and in-situ DRIFTS measurement,it can be proved that Cu/MgO catalyst was followed an associated mechanism in WGS reaction,which was the reaction between CO and-OH,because it cannot dissociate water to hydrogen directly.Combined with the results of the reactivity without adding H2O during the reaction,it was revealed that the-OH was derived from the dissociation of the reactant H2O and the surface-OH of Mg(OH)2.(4)Construction of high-efficiency redox carrier supported catalyst for WGS reaction:an efficient ceria surface highly activated by Au clusters for WGS reactionCeria-based catalyst is a promising water-gas shift reaction(WGS)catalyst,and its activity is extremely sensitive to structure.Therefore,the preparation of highly efficient ceria-based catalysts is challenging and urgently needed.Generally,high-temperature calcination of ceria was adverse to the formation of oxygen vacancies,which were important for the rate-determining step of WGS reaction.However,this intrinsically inert surface of ceria was modified by self-induced clustered gold atoms and showed very high activity in dissociating water molecules.An additional high-temperature pre-oxidation treatment of the ceria support before loading Au species enhanced its WGS reactivity by four times.Subsequent in-situ DRIFTS and in-situ Raman results revealed that the improved efficiency of dissociated water on the surface of ceria was derived from the modification of surrounding Au clusters.The pretreatment on the surface of ceria skillfully regulated the location of Au species.Gold clusters and ceria surface interacted with each other and jointly promoted the WGS reaction. |
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