| Ceria is an important catalyst component widely applied in many fields,which include but not limited decontamination of vehicle exhausts,VOCs elimination,water gas shift reaction and reforming.Its preparation methods mainly include sol-gel,precipitation,hydrothermal and chemical template method.However,these methods have their own disadvantages.For example,the product prepared by sol-gel method is easy to sinter;the hydrolysis rate of precipitant needs to be strictly controlled in precipitation method;the equipment of hydrothermal method is expensive;and the process of chemical template method is complicated.Besides,biotemplates have attracted extensive attentions owing to their structural diversity,low cost,availability and environmental protection.Among them,the BSA molecule has a multi-level and multi-dimensional structure,which is different from the general chemical molecular structure.It can encapsulate and stabilize metal ions,and is expected to be a good soft template.Therefore,exploring the BSA template to prepare CeO2 with different structure is the focus of this study.With BSA as the biotemplate,CeO2 is prepared by citrate acid assisted sol-gel method.The effect of the BSA template on CeO2 structure is systematically investigated by characterization techniques such as scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectroscopy,nitrogen adsorption-desorption(BET)and transmission electron microscopy(TEM).The results demonstrate that the BSA template can effectively improve the structure of CeO2,leading to a hierarchically porous structure.The use of BSA template could increase the pore size,pore volume and specific surface area of CeO2.In addition,it could retard the sintering and growth of CeO2 grains.So the grains of BSA templated CeO2 have better dispersion.The synthesis mechanism of porous CeO2 by the BSA template is analyzed.It is considered that the BSA molecular plays a significant role in dispersing and capping the CeO2 precursor sol.Then,the hierarchically porous CeO2 is used as a support to prepare Au/CeO2 catalyst by deposition-precipitation method,and its advantages in catalytic applications is explored.It is found that the catalyst possesses smaller Au particles(3.2 nm)and higher actual Au loading of almost 100%out of theoretical loading,and exhibits better catalytic performance for the benzene oxidation(T90%=210?),and its activity remains stable over 140 h of on-stream reaction.The H2-TPR results indicate that the smaller Au particles interact more strongly with the CeO2 support to promote the reduction of surface oxygen species.Thus the reactivity of CeO2 surface oxygen is higher,which is to the benefit of benzene oxidation.Finally,it is proposed that the catalytic process for benzene oxidation over Au/CeO2 catalyst is the dual sites mechanism.Moreover,copper source is introduced in the BSA templated synthesis of CeO2,and the effect of BSA on the surface structure of the complex oxides is investigated.The result shows that,with BSA as the template,CuO/CeO2 catalyst with uniform CuO species is produced.The as-produced CuO/CeO2 catalyst shows a higher catalytic activity for CO oxidation(T100%=90 ?)and good stability.At the same time,the influence of calcination temperature and atmosphere on the dispersion of CuO species is investigated.It can be observed that the higher temperature is beneficial to generate highly dispersed CuO species,however,catalyst particles easily sinter.Among them,the catalysts calcined at 500 and 600 ? have better dispersion of CuO species,resulting in the better catalytic performance for CO oxidation.The H2-TPR and CO pulse adsorption results show that the highly dispersed CuO species have a strong synergistic effect with CeO2 support,which improves the reducibility of CuO species and CO adsorption.The treatment at high temperature in N2 could prevent grain growth.And the copper species are mainly distributed on the CeO2 surface,which results in the decrease of CuXCe1-XO2-? solid solution.However,its activity is higher,indicating that the surface CuO species play a greater role.It further shows that compared with oxygen vacancies,the adsorption of CO is a key factor for affecting activity of the catalyst. |
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