| At present,the fossil fuels such as coal,natural gas,oil are the primary energy sources.However,the excessive utilization of these fuels causes the sharp decline in their reserves and increase in CO2 concentration.Converting CO2 into valuable chemicals and fuels is one of the most practical ways to reduce CO2.Although great efforts have been made in heterogeneous CO2 reduction in recent years,it is still challenging to develop catalysts with high activity,selectivity and stability to fulfill this goal.MeOH is one of the main liquid products of CO2 reduction.As the starting material of the chemical industry,it is a very important chemical and fueladditive.In addition to MeOH,hydrocarbons also play a very important role in industry.On the other hand,the photothermal catalysis is an ideal way for the combination the advantages of both the traditional thermal catalysis and photocatalysis.The photothermal catalysis can not only reduce the activation energy of the reaction and reduce the reaction temperature,but also improve the catalytic activity of the photocatalytic reaction.Therefore,the photothermal catalytic CO2 hydrogenation is highly important.Based on these,in this thesis,we developed many catalysts and used them in thermal or photothermal CO2 hydrogenation to methanol or hydrocarbons.The relationship between the catalyst structure and the catalytic performances were investigated,and the possible catalytic mechanisms were also proposed.The main contents are as follows.(1)A several of Pt/ZSM-5 catalysts with different Si/Al ratios(50,360,and 5000)were prepared via an impregnation method and used in aqueous CO2 hydrogenation to produce methanol.It was found that the basic property of the catalyst was affected by the Si/Al ratio of the ZSM-5 support,which further influenced the catalytic performances.The basic strength of the catalyst declined with increasing the Si/Al ratio.A suitable base strength is benefit for the reaction,and the best results were obtained at the Si/Al ratio of 360,180℃,12 h,2 MPa CO2 and 6 MPa of H2,respectively.Under the optimal conditions,the STY and selectivity of methanol reached to the values,i.e.,0.38 mmol·mmolpt-1·h-1 and 83%,respectively.(2)Several trimetallic Co-Cu-Mn oxide catalysts were prepared via a coprecipitation method followed by a partial reduction step,which were applied in photothermal CO2 reduction to hydrocarbons.The metal composition and reduction temperature of catalyst had a great impact on its structure and photoelectric characteristics,which simultaneously affected the catalytic performances.The novel Co7Cu1Mn1Ox(200)catalyst,reduced at 200 ℃ under H2 for 2 h,showed multi-functional applications in the formation of methane and C2+hydrocarbons for its complex composition,and it can provide 14.5 mmolCH4·gcat-1·h-1 at low CO2 and H2 concentrations(CO2/H2/N2,10%/30%/60%).The present strategy for constructing trimetallic catalyst with partial reduction does not only provide a highly active catalyst for photothermal CO2 reduction,but also offer a potential possibility for reducing the reaction temperature for the conventional thermal reactions.(3)A series of bimetallic Co-Cu oxide catalysts were prepared by the coprecipitation method and applied in the photothermal CO2 reduction to produce hydrocarbons.The catalyst was characterized by XRD,N2 physical adsorption,and chemisorption,etc.The results showed that the metal composition of the catalyst has a great influence on its structure,which further affects the catalytic performance.The Co9Cu1Ox catalyst exhibited a high activity and a high selectivity in the formation of C2+hydrocarbons.The activity of C2+hydrocarbons can reach 18.6 mmol·gcat-1·h-1 and the selectivity reaches 60%under the optimum conditions. |
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