Properties Study Of Ceria Supported Au Catalyst In Catalyzing CO Oxidation And Water Gas Shift Reactions

Since 1987,Japanese scientist Haruta et al.have found that nano-scale gold supported on metal oxides exhibits excellent catalytic performance for CO oxidation reaction,supported nano-gold catalysts have received widespread attention.As the research continues to deepen,everyone is arguing over the sources of high activity of gold catalysts.The valence state of gold species has an important influence on the catalytic activity.Everyone has a word about the contribution of various gold species to the catalytic reaction,so the determination of true active site remains blurred.The predecessors have done a lot of work on this,but it is still difficult to reach a consensus.There are two main reasons for this:First,the complexity of the research system itself,it is often impossible to prepare supported nano-gold catalyst with a single species in the actual operation.As for the same catalyst,there may be gold species in various states;in addition,even though the same catalyst,because of the different preparation conditions,reaction conditions,etc.,it is difficult to make an effective comparison.Therefore,it is very critical to find an optimal system for research.Second,the characterization of catalyst structure is not detailed and completed,and some conventional characterization methods have been difficult to monitor real-time catalytically active centers under reaction conditions.This requires some in-situ testing to aid research.On the other hand,the nature of the support is also an important factor in affecting the catalytic activity.As a relatively common rare earth oxide,cerium oxide has unique variable-valence properties and thus has strong storage and release oxygen capacity,so it is widely used in the field of catalysis.In this work,we selected CeO2 nanoparticles as a support,and synthesized a series of catalysts by deposition-precipitation method.The specific research contents are as follows:1.Effect of structural evolution of gold species supported on ceria in catalyzing CO oxidationThe intrinsic activity of atomically dispersed gold catalysts for low-temperature(L-T)CO oxidation remains a vague problem.Here,we prepared two different loading of gold catalysts by DP method for evaluation of their reactivity in L-T CO oxidation.From the different catalytic behaviors we found:These weakly anchored gold atoms present in the 1%Au/CeO2 catalyst showed increased reactivity under reaction conditions,while for 0.5%Au/CeO2,there is no change in the reactivity of these strongly bonded gold atoms in the catalyst.In situ DRIFTS demonstrated that the gold structure changed during the reaction,and the ac-STEM images also confirmed that the atomically dispersed gold in the 1%Au/CeO2 catalyst became gold clusters with increasing activity.CO adsorption spectroscopy combined with kinetics measurements showed that the ability of gold clusters to adsorb CO molecules is stronger than that of gold single atoms at room temperature.Therefore,the difference in the ability to capture CO molecules is a major factor contributing to the difference in activity for 1%Au/CeO2 and 0.5%Au/CeO2 catalysts.2.Exploration of intrinsic activity of supported gold catalysts in catalyzing water gas shift reaction.Supported Au catalysts have high activity in low temperature,wide active temperature range,good oxidation resistance and water resistance.Therefore,it is considered to be one of the best WGSR catalysts for PEMFC demanding harsh operating environments.Here we also used the above method to prepare three comparable catalysts with different gold loading for the study of water gas shift reaction.The catalyst was characterized by a series of characterization methods such as HRTEM,H2-TPR,XPS and DRIFTS.We found that the catalytic activity of WGSR increased with the increase of gold loading.The H2-TPR results showed that the interaction between gold and support was distinguishing in different Au/CeO2 samples.The in situ DRIFTS results indicated that the atomically dispersed gold cations were all reduced to gold clusters under reaction condition.The difference in activity may be resulted from the increase in the concentration of the catalytically active sites on the surface of the catalyst as the gold content increases,resulting in the efficient adsorption of CO and the dissociation of water.The TPSR experiments treated quantitatively confirmed that the reaction mechanism is a synergistic mechanism.