Studies Of Single-atom Pt-based Catalysts For Carbon Dioxide Reforming Of Methane

Today the adjustment of energy structure and the protection of environment are the social focus of the sustainable development.The carbon dioxide reforming of methane reaction can not only effectively utilize greenhouse gases,but also convert reactive gases into synthesis-gas which can be used in Fischer-Tropsch reaction with H₂/CO ratio being close to 1:1.The noble metal catalysts have excellent catalytic performance and the good ability of resistance to carbon deposition,but the high price limits their application in carbon dioxide reforming of methane.Nowadays,single-atom catalysts are becoming more and more important because of the effective use of metal atoms,but they are easy to sintering under high reaction temperature,which results in the decrease of catalytic activity.So improvement of the thermal stability of the single-atom noble catalysts can increase the utilization of noble metals and decrease the sintering of the catalyst,which has a positive effect on carbon dioxide reforming of methane.Thus the main point of the single-atom catalyst is how to anchor the active metals on the catalyst surface with high dispersion.In the first part of this research work,the single-atom Pt catalysts were successfully synthesized by supporting Pt on CeO₂ materials with different morphology,such as CeO₂-NRs?nanorods?,CeO₂-NPs?nanoparticles?,CeO₂-NCs?nanocubes?and so on,under high calcination temperature?800^°C?,and these catalysts were labeled as 1%Pt/CeO₂-NRs-800^°C,1%Pt/CeO₂-NPs-800^°C and1%Pt/CeO₂-NCs-800^°C,respectively.The investigation results showed that compared with the conventional Pt catalyst,the single-atom Pt catalyst could increase the atomic utilization rate of the active metal Pt and accordingly increase the number of active sites on the surface of the catalyst.The catalytic activities of these catalysts were investigated in the carbon dioxide reforming of methane reaction,and the results showed that the three kinds of single-atom catalysts all exhibited higher catalytic activity than the conventional Pt catalysts.As for the three different single-atom catalysts supported on different CeO₂ materials,their catalytic activities showed the following order:1%Pt/CeO₂-NRs-800^°C>1%Pt/CeO₂-NPs-800^°C>1%Pt/CeO₂-NCs-800^°C.The reason of the better catalytic activity of 1%Pt/CeO₂-NRs-800^°C catalyst than the other two catalysts was mainly due to the exposed?111?crystal plane of CeO2-NRs support.But after treatment by H2,the Pt ions on the surface of the single-atom catalyst were reduced to Pt⁰ and the Pt⁰ particles would grow bigger,and finally exhibited similar catalytic activity as the conventional catalyst.In the second part of this research work,the single-atom Pt catalyst?0.2%Pt-mAl₂O₃-Direct?was designed and prepared by supporting Pt on mesoporous Al₂O₃,which was compared to the conventional catalyst?0.2%Pt-mAl₂O₃-Impregnation?.The results showed that 0.2%Pt-mAl₂O₃-Direct had the better catalytic activity and stability than 0.2%Pt-mAl₂O₃-Impregnation catalyst.The Pt ions on the surface of the 0.2%Pt-mAl₂O₃-Direct catalyst were anchored by the special pentacoordinated bond of Al2O3.Even after the treatment by reducing gas,the coordination bond could fix the Pt⁰ atoms and prevent them to grow up to bigger nanoparticles.Thus the single-atom catalyst 0.2%Pt-mAl₂O₃-Direct exhibited the consistent catalytic activity and stability even after reducing treatment of hydrogen under high temperature.