Preparation Of MFe-PBA (M=In, Fe) Derived Catalysts And Study Of Their Photothermal Catalytic CO₂ Hydrogenation Performanc

With the development of the social economy,fossil energy has been consumed in large quantities,and then a large amount of CO₂ emissions have been produced,resulting in energy crisis and environmental problems becoming increasingly prominent.Converting CO₂,a greenhouse gas,into reusable high-value-added chemicals would not only alleviate the energy crisis,but also have a positive impact on the environment.Therefore,catalytic conversion of CO₂ into reusable chemical fuels by photocatalysis or photothermal catalysis using clean solar energy is a promising approach.In this paper,a transition metal oxide catalyst with high activity was constructed by using low-cost Fe-based Prussian blue analogs（PBA）,and its photothermal co-catalytic performance for CO₂ hydrogenation was investigated.Meanwhile,the relationship between catalyst performance and structure was analyzed by various characterization techniques,and the reaction mechanism was revealed.The main research content of this thesis is as follows:（1）Preparation,characterization,performance of photothermal catalytic,and mechanism of the bimetallic oxide catalyst InFe-x.A series of bimetallic oxide catalysts InFe-x（x represents the pyrolysis temperature）were obtained by calcination of InFe Prussian blue analogs（InFe-PBA）in air by co-precipitation method.XRD,FT-IR,Raman and TEM characterization techniques were used to demonstrate that the catalyst is composed of iron ion doping and amorphous ferric oxide heterostructure and the the relationship of structure and composition of the catalyst is closely related to the calcination temperature.Compared with the monomeric oxide,the catalyst constructed by using InFe-PBA precursor has strong interaction and good dispersion at the interface between the active component iron oxide and indium oxide.The experimental results showed that the catalyst annealed at 600℃showed the best CO₂ reduction performance,and the CO yield surpassed 5 mmol g^-1 h^-1,which was 5.5 times of pure indium oxide and 2.3 times of pure iron oxide.Continuous stability tests for nearly 50 hours demonstrated good stability of the catalyst.The mechanism study shows that the introduction of iron not only promoted the absorption of visible light,but also reduced the energy barrier of CO₂ activation.Through the CO₂/H₂-TPD technique,it was revealed that catalysts derived from PBA are more likely to activate CO₂ and H₂.The reaction pathway for CO₂ reduction was demonstrated by in situ DRIFTS,indicating the reverse water gas shif（RWGS）reaction.The significant improvement of catalyst performance is due to the construction of indium oxide and ferric oxide heterojunction and the doping of iron ion,the interfacial interaction between crystalline indium oxide and amorphous ferric oxide and the ion doping improve the separation efficiency of photogenerated carrier and the solar absorption performance.（2）Preparation,characterization,photothermal performance and mechanism of iron-based catalysts..Iron-iron Prussian blue analogues（FeFe-PBA）were prepared by co-precipitation,and a series of iron-based catalysts such as α-Fe₂O₃,γ-Fe₂O₃,Fe₃O₄,Fe O,Fe and so on could be optimized by adjusting the H₂ reduction temperature.Through XRD,FT-IR,Raman,XPS,DRS and other characterization techniques,it is known that the heat treatment reduction temperature has a direct effect on the chemical valence state of iron in the catalyst and the phase of iron oxide.The photothermal catalytic CO ₂hydrogenation performance showed that the rate of the product production significantly depended on the composition of the catalyst.The activity of CO showed three continuous volcanic shapes,and the related optimal catalysts wereα-Fe₂O₃/Fe₃O₄,γ-Fe₂O₃/Fe₃O₄ and Fe/Fe_xO_y heterostructures.The activity of CH₄ and C₂-C₄ products mainly occurred in the Fe/Fex O_y catalyst that was obtained by high-temperature reduction.The catalytic mechanism study found that in the process of photothermal catalytic reaction,α-Fe₂O₃ and γ-Fe₂O₃ were basically converted to Fe₃O₄,which was the main active component of RWGS.In particular,,the α-Fe₂O₃/Fe₃O₄ andγ-Fe₂O₃/Fe₃O₄heterojunction structures have excellent CO generation rates.Fe/Fe_xO_y（Fe/Fe₃O₄/Fe O）can overcome the C-C coupling reaction barrier due to the excellent surface plasma effect of metal Fe and the heterojunction interface of metal/oxide,which is more conducive to hydrogenation and the formation of multi-carbon products.During the catalytic reaction at lower temperature,the α-Fe₂O₃ catalyst underwent partial structural transformation,and the so-formed α-Fe₂O₃/Fe₃O₄ heterojunction showed good RWGS activity.Although the γ-Fe₂O₃maintained the inital structure during the catalytic reaction,it showed no any activity towards CO₂ hydrogenation.