Hydrogenation Of Carbon Dioxide To Methanol Through Plasma Catalysis Over Iron-based Catalysts

Carbon dioxide?CO₂?,the main greenhouse gas,is also a kind of cheap carbon resource.The conversion of CO₂ to value-added chemicals will greatly benefit people's manufacturing and life.Different from the traditional thermal-catalysis,the combination of dielectric barrier discharge?DBD?plasma and catalyst can directly hydrogenate CO₂ to CH₃OH at low temperature and atmospheric pressure.In this thesis,iron has been chosen as the active metal,and the advantage of the synergy between the catalyst and plasma has been used to improve the catalytic activity.Following experimental results and conclusions have been achieved:1.In the case of only plasma,the conversion of CO₂ and the selectivity of CH₃OH would be significantly affected by the reaction conditions.The optimized reaction conditions for the hydrogenation of CO₂ to CH₃OH are as follows:60 ^oC recycled water,75 ml/min gas velocity,CO₂:H₂=1:3 and 18 W discharge power.2.For Fe-based catalysts,supports with different adsorption properties and dielectric properties dramatically affect the catalytic performance.Notably,?-Al₂O₃which has stronger CO₂ adsorption ability and relatively smaller dielectric constant is conducive to the generation of plasma,and then promotes the formation of CH₃OH.Differently,TS-1 with weak acid property is favorable for the formation of acetic acid.3.Loadings of Fe-?-Al₂O₃ catalysts showed the volcanic curve relationship with catalytic performance.Fe-based catalyst with 5 wt.%loading exhibited the best catalytic activity,i.e.,11.7%CO₂ conversion and 57.9%CH₃OH selectivity.It can be further speculated that low loading of iron-based catalyst is responsible for the high dispersion of Fe,which produce more active sites,thus promote the production of CH₃OH.4.Catalyst characterization and plasma diagnostic results indicate that the amount of oxygen vacancies shows linear relationship with the catalytic performance,thus it can be speculated that oxygen vacancies is highly to be the active sites for the hydrogenation of CO₂ to CH₃OH.Moreover,based on the activation energy of the elementary reactions in CO₂/H₂ plasma,the main reaction pathway of CH₃OH synthesis has been proposed:CO₂?CO*?COH*?HCOH*?H₂COH*?CH₃OH*.