Catalytic Performance And Structure-Property Relationship Of Cu/TiO₂ Nanosheet Catalysts For CO₂ Hydrogenation To Methanol

Copper is widely used as the active component of catalysts toward CO2 hydrogenation to methanol,due to its low cost and capability to activate H2.And metal oxides are often constructed as the support of these catalysts,the easily-formed defect sites of metal oxides are usually reported to activate CO2 effectively;furthermore,different kinds and quantities of defect sites lead to distinctive catalytic performance of these catalysts.In addition,both the structural interactions and electronic interactions between Cu and metal oxides play important roles in their catalytic performance,and the morphologies and exposing facets of the metal oxides influence the interactions between Cu and metal oxides.The anatase TiO2 nanosheets(-ns-)were investigated in this research work due to its largely exposed highly active(001)facets and impressive two-dimensional nanosheet shape.The bicomponent catalysts containing Cu and TiO2-ns display highly enough catalytic activity toward methanol synthesis.In this work the optimal catalyst synthesis conditions were explored and the interactions between Cu and TiO2-ns were researched,and the structure of active sites of Cu/TiO2-ns was also revealed.The main research contents and conclusions of this dissertation were listed as below.1)The highly exposed highly active(001)facet anatase TiO2 with regular nanosheet shape were synthesized,by using hydrofluoric acid as capping agent;copper was loaded on TiO2-ns through deposition-precipitation method.Various loading amounts of copper,different calcination temperature and different reductive atmosphere lead to quite different catalytic performance of Cu/TiO2-ns catalysts.Cu/TiO2-ns with the copper loading amounts of around 30 wt%,calcination at 400 ? and activated with low concentration of hydrogen displayed the highest activity.Under the reaction conditions,pressure = 3 MPa,temperature =260 ? gas hourly space velocity = 3600 mL�g-1�h-1,the methanol yields of the optimal catalyst reached 5.6%.The structural characterization of Cu/TiO2-ns catalysts were conducted with Raman,XRD and BET;the defect sites of catalysts Cu/TiO2-ns were characterized by EPR;the particle sizes of Cu and the amounts of Ti3+ were indicated to be the main factors to affect their catalytic activities.2)The anatase TiO2 nanoparticles(-np-)with nearly the same surface area to Ti02-ns were used as support to construct the reference Cu/TiO2-np catalyst.There was no detectable EPR signals of Ti3+ and incorporated Cu2+ over Cu/TiO2-np;however,both were detected over Cu/TiO2-ns catalysts,which indicates that the structural interactions between Cu and TiO2-ns is distinctive.In addition,the results of in-situ XPS display that there is a much noteworthy band bending effect between Cu and TiO2-ns,which indicates the electronic interaction between Cu and TiO2-ns is much stronger,and Ti3+ persistently existed on Cu/TiO2-ns during the whole reaction process of in-situ XPS characterization.The CO2-TPD and FTIR characterization display that there is much larger amount of moderately adsorbed carbon species derived from CO2 on Cu/TiO2-ns.Combine with the much lower methanol-synthesis catalytic activity of Cu/TiO2-np than that of Cu/TiO2-ns,the defect sites Ti3+ are demonstrated to be highly active toward CO2 activation and the interfaces of Cu and TiO2-ns are inferred to be the active centers which catalyze the hydrogenation of CO2 to methanol.