Development Of Indium Oxide Based Catalysts For Photothermocatalytic CO₂ Reduction Application

A new era with energy crisis induced by worldwide fossil fuel depletion and cumulative greenhouse CO₂ emission increase attention of researchers on solving serious environmental and energy issues.photothermocatalytic CO₂ reduction take advantages of clean solar energy irradiating on catalysts surface and further driving the catalytic conversion of gas molecules.In addition to intensive light absorption and high light-to-heat conversion efficiency,catalysts are also expected to own high concentration of active sites in where reactants could attach on and be converted to production.This work is inspired by traditional thermal chemical catalyst as study object and extends to exploit high reactivity,selectivity,and stability photothermocatalysts by tuning the microscopic morphology and electronic structure.The contents of the thesis are as following:（1）2D black In₂O_3-xnanosheets were prepared via simple hydrothermal synthesis and subsequent in-situ photothermal treatment under reaction atmosphere.The fast photothermal treatment endowed the obtained In₂O₃ the nanosheet structure derived from In（OH）₃ precursor,which generated high-concentration oxygen vacancies（O_v）on the surface.These oxygen vacancies possess bifunctions of working as active sites for reverse water-gas shift reaction and introducing defect level in band gap that extended the range of absorption（>2400 nm）.These novel features of In₂O_3-x nanosheets enhanced photothermal conversion efficiency（reaching 350℃in 10 min）and achieved103.2 mmol g_cat^-1 h^-1 of CO yield rate with almost 100%CO selectivity.（2）Carbon doped indium oxide(C-In₂O_3-x)as a photothermal catalyst was prepared via hydrothermal synthesis.Confirmed by experimental and theoretical results,carbon atom tended to be interstitial doping,which reduced formation energy of oxygen vacancies and thus leaded to dense oxygen vacancies on the In₂O₃.The synergy between carbon atom and oxygen vacancy prompted photothermal conversion（reaching 400℃in 10 min）.C-In₂O_3-x overcame the challenges of deactivation caused by nanostructured collapse at high temperature,and realized 20 hours steady CO production(with an average yield rate of 123.6 mmol g_cat^-1 h^-1).（3）The photothermal CO₂ reduction catalyst was made of graphene and In₂O₃compound（G-In₂O₃）,and potassium dopingγ-Fe₂O₃（K-Fe₂O₃）.Dual bed affiliation architecture enabled layered reaction temperature modulation.The upper layer catalyst G-In₂O₃ with high photothermal conversion was responsible for reverse water-gas shift reaction.Emitted thermal radiation was transferred from the graphene to the K-Fe₂O₃in lower layer to promote Fischer-Tropsch synthesis reaction.Potassium doping was benefit to transform from Fe₂O₃to Fe₅C₂ and enhanced the light olefins selectivity.The multilayered enthalpy heat-recovery systems were applied to photothermal CO₂production（CO₂:H₂=1:5）with 46%and 20%selectivity for C₂H₄ and C₃H₆production,respectively.