Study On The Preparation Of Pt-Based Catalysts And Photothermalcatalytic Reduction Of CO₂

With the rapid consumption of many natural resources,especially fossil energy,and in the process of the fossil energy such as oil and coal consumption continuously produce CO₂ continues to cause great pollution to the environment,such as the greenhouse effect,in this grim situation,for renewable energy and mitigation of CO₂emissions has become urgently needs to solve the problem.To forge ahead in the direction of sustainable development,the full use of solar energy to convert CO₂ into clean energy has gradually attracted people’s close attention.Photocatalytic methane and carbon dioxide dry reforming not only utilizes solar energy and deals with greenhouse gases,but also generates H₂ and CO,which can be stored and utilized,effectively provides excellent solutions to environmental pollution and energy shortage.The catalytic activity of Ni and Co in non-noble metals is high,but the carbon resistance is poor,so it is easy to deactivate.However,precious metals such as Pt,Ru and Rh,which have high catalytic activity,stability and strong anti-carbon deposition performance,cannot be used in large-scale production due to their high cost and limited resources.If the content of precious metal is low,its activity and light absorption intensity will be greatly reduced although the cost is reduced.In this paper,with trace precious metal Pt as the active component and Co-doped Al₂O₃ as the carrier,the catalyst Pt/Co-Al₂O₃ was prepared,and its catalytic activity was tested by using 500W Xe light source to drive the photothermal catalytic methane carbon dioxide dry reforming（CRM）.The mechanism of high catalytic activity and light-to-fuel conversion efficiency of the catalyst was studied.The research results of this paper are as follows:1.Using aluminum nitrate（Al（NO₃）₃）,cobalt nitrate（Co（NO₃）₂）and urea as raw materials,catalyst carriers（Co-Al₂O₃）with different hydrothermal temperatures（120℃,150℃,and 180℃）and different cobalt content（1%,3%,and 5%）were prepared by hydrothermal method.Then dilute platinum nitrate（Pt（NO₃）₂,Pt18.02wt%）was ground and loaded on Co-Al₂O₃（platinum element accounted for 0.5wt%of the mass of Co-Al₂O₃ carrier）.BET analysis showed that under the same hydrothermal reaction temperature（150℃）,the specific surface area decreased gradually with the increase of cobalt content.Under the condition of the same cobalt content（5%）,the specific surface area decreased gradually with the continuous increase of hydrothermal reaction temperature.With the photocatalytic CRM test,it was found that Pt/Co-Al₂O₃ catalyst with cobalt content of 5%at hydrothermal temperature of150℃had the best catalytic activity.UV-vis-IR absorption spectrum analysis showed that the higher the cobalt content of the catalyst,the stronger the light absorption.2.A novel nanocomposite of Co doped Al₂O₃ nanosheets supporting Pt nanoparticles（Pt/Co-Al₂O₃）was prepared.By merely utilizing focused UV-vis-IR illumination from a 500 W Xe lamp,highly efficient photothermocatalytic CO₂reduction by CH₄（CRM）on Pt/Co-Al₂O₃ is achieved.It demonstrates very high production rates of CO(r _CO,89.41 mmol min^-1g^-1)and H₂(r _H2,75.60 mmol min^-1g^-1),and large light-to-fuel efficiency（η,27.2%）,enhanced by 5.4,6.0,and 6.2 times as compared to those of Al₂O₃ nanosheets supporting Pt nanoparticles（Pt/Al₂O₃）.Pt/Co-Al₂O₃ also demonstrates good catalytic durability as the side-reactions of coke deposition is significantly blocked.In striking contrast,Pt/Al₂O₃ quickly deactivates due to its high coke deposition rate（r _C）,15.3 times higher than that of Pt/Co-Al₂O₃.The significantly promoted photothermocatalytic performance arises from a synergetic effect between Pt and Co-Al₂O₃.The formation of Pt/Co-Al₂O₃ interface significantly promotes CH₄ dissociation to carbon species as compared to Pt/Al₂O₃,thus raising catalytic activity.The active oxygen of Co-Al₂O₃ participates in the oxidation of carbon species as rate-determining step of CRM,thus not only raising catalytic activity but also blocking carbon species being polymerized to coke.The photothermocatalytic CRM on Pt/Co-Al₂O₃ follows a mechanism of light-driven thermocatalysis.The intense absorption across whole sunlight spectra of Co-Al₂O₃ induced by Co doping substantially intensifies the photothermal conversion of Pt/Co-Al₂O₃,thus improving catalytic activity.A novel photoactivation is discovered to considerably raise catalytic activity due to the oxidation of carbon species being promoted upon illumination.