Study On The Catalytic Hydrogenation Of CO₂ By Ruthenium/Cerium Oxide Under Photothermal Condition

In recent years,with the rapid development of the global economy and society,serious crisis had raised on energy and ecology due to the excessive consumption of limited fossil fuels with abundant carbon dioxide being released.Energy crisis and greenhouse effect can be effectively relieved if carbon dioxide can be reused.Among various reuse routes,hydrogenation of CO2(as Cl raw material)to hydrocarbons has attracted considerable attention.At present,the hydrogenation reaction was nearly based on thermo-chemical reduction method,which leads to inevitable consumption of additional energy.The utilization of solar energy to drive the hydrogenation of carbon dioxide is hopefully to reduce the dependence of fossil fuels as thermo source,whereas it has rarely been addressed.Besides,it is unclear that whether there is a difference between thermal and photo-thermal process in CO2 reduction.Based on the above research background,this work focused on the hydrogenation of CO2 under thermal process or photo-thermal process using Ru/CeO2 as the model catalyst.We studied the inner connection between concentration of oxygen vacancy in CeO2 and efficiency of CO2 conversion.And the function mechanism of crystallographic planes of CeO2 on the CO2 methanation was also investigated under photo-thermal condition.This work mainly consists of the following two parts:(1)Synthesis of Ru/CeO2 catalysts and their catalytic performance towards the hydrogenation of CO2.We firstly prepared CeO2-cube and CeO2-rod as catalyst support,and 1.5 wt%Ru was loaded to obtain Ru/CeO2 catalysts.The catalytic performances of these two catalysts were evaluated for the hydrogenation of CO2 in a home-made flow cell at normal pressure.Under two different reaction conditions of thermal and photo-thermal process,the behaviors of these catalyst were investigated and the reason was discussed.The results showed that both catalyst were more efficient under photo-thermal condition than that under thermal condition.For instance,nearly 100%conversion of CO2 could be achieved at 220℃ on Ru/CeO2-rod catalyst under photo-thermal condition,while only 40%of CO2 was reduced under thermal condition.Furthermore,the conversion efficiency of CO2 is closely related to the microstructure of CeO2,and Ru/CeO2-rod is generally superior than Ru/CeO2-cube.(2)Utilization of various techniques to reveal the factors and mechanisms in photo-thermal reduction of CO2.Raman and XPS characterization results indicated that the high activity of Ru/CeO2-rod was closely related with the abundant oxygen vacancies.Further theoretic calculation demonstrated that existence of oxygen vacancies reduced the adsorption energy of CO2,and facilitated the adsorption and conversion of CO2.This finding also explained the higher catalytic activity of the Ru/CeO2-rod than that of Ru/CeO2-cube.In-situ FTIR was used to analyze the intermediate species and explore the reaction route for the CO2 methanation.The results showed that illumination facilitated the conversion of intermediate species and a high conversion of CO2 was achieved as a result.