Photothermal Catalytic Synthesize Of Syngas From CH₄ Reforming Of CO₂ With Rh-Cu Composite Metal And Direct Carbonylation Reaction Of Syngas

The activation of inert C-H bond(bond energy 439 kJ/mol)is the fundamental and common reaction step for the design of complex molecular structures of methane.It has been a challenge to achieve the activation of the inert C-H bond through the photocatalytic pathway in both thermodynamics and kinetics.Recently,it is a new and efficient method to promote the activation of high energy C-H bonds by a concerted catalytic process that using solar energy as the only energy source to create the combine of photo field and thermal field action conditions simultaneously.In this work,photo-thermal co-catalysis is used as the design core to avoid the direct activation of inert CH4 and thermodynamic and kinetic restriction of multi-carbon coupling.We established a local surface plasmons resonance system enhanced by Rh-M-Al2O3 multi-element.Multi-carbon transformation and fixation are realized through the CO2 dry reforming of CH4 to generate CO and carbonylation of CO in the photo-thermal system.A class of indirect conversion strategy for transformation of inert C1 molecules such as CH4 and CO2 to multi-carbon organic products is designed by the pathway of activation and the reconstruction of molecular.The main conclusions of this thesis are as follows:(1)The single noble metals(Pt,Pd,Ru,Rh)loaded M-Al2O3 exhibited a property of local surface plasmons resonance which could enhance the thermal effect of the catalyst excited by sunlight(200-1050nm)and they can effectively initiate the CH4 reforming of CO2 to syngas under sunlight irradiation.The temperature rise of this system is caused by the coupling of hot electrons with phonons which is generated by photoexcitation.Different property of valence electron is the decisive factor for plasma effect of the noble metal catalysts.Under the same sunlight intensity condition,Rh metal catalyst showed better photocatalytic efficiency than other noble metals(Pt,Pd,Ru)and obtained the highest yield in methane reforming reaction.When the sunlight intensity is 3W,the yield of CO and H2 are 63.29mmol.g-1.h-1 and 72.15mmol.g-1.h-1,respectively.(2)Introduction of transition metals(Co,Ni,Cu)with different electronic structures could improve the efficiency of methane reforming and Cu have thebestperformance in accelerating the reaction.The binary composite metal photocatalyst Rh-Cu/Al2O3 prepared by in-situ photoreduction exhibits a full-spectrum absorption property in the UV-Vis-NIR.Rh-Cu/Al2O3 with optimized doped proportion in continuous flow reaction mode could increase the single conversion up to 43%for CH4 and 55%for CO2,simultaneously.The CO and H2 yield are reached 500.12 mmol.g-1.h-1 and 642.76 mmol.g-1.h-1,respectively,selectivity of CO was more than 90%.Compared to Rh-Cu/Al2O3 catalysts,Rh-Cu/Al2O3 has a stronger near-field enhancement effect and a weaker electron-phonon coupling effect and hotter electron generation or longer hot electron lifetime irradiated by full-spectrum sunlight cause by local plasmon resonance effect,which are the essential reasons for improving the efficiency of the methane reforming reaction.(3)CO which is the main product as the starting material,can react with halogenated aromatics,organic amines/alcohols and successfully synthesized nearly ten amide/ester compounds.under photo irradiation.plasma-assisted dry methane reforming integrated with combined CO2 methane reforming is an effective way to deliver syngas for multi-carbon production.The innovation of this article is stated as follows:(1)taking the photo-thermal cooperative catalyst which has the surface plasma resonance effect as the main component(Rh-Cu/Al2O3),the indirect activation and reformation of Cl molecules typical represented by CH4 and CO2 can be efficiently realized under relatively mild conditions without additional thermal compensation.(2)CO as a main product to participate in the carbonylation reaction with halogenated aromatic hydrocarbons and organic amines/alcohols to accomplish the fixation of methane and molecular transformation for organic synthesis.This provides a novel photocatalytic approach for efficient conversions of the two gases using solar energy.