Study On The Synthesis Of Ni/CeO₂ And Its Catalytic Activity Towards Hydrogenation CO₂ Under Photothermal Condition

With the rapid increase in world economy,large amounts of CO2 are emitted with the consumption of people in the process of fossil fuels,and the increased concentration of CO2 results in serious greenhouse effect.How to transform and utilize CO2 have received more and more attention,also turning CO2 into more valuable raw materials is also the focus of government study.At present,the study of CO2 methanation is based on thermal catalytic,which inevitable result extra energy consumption.In this study,we propose to use sunlight as the energy source to drive CO2 hydrogenation.This strategy will not only reduce the dependence of fossil energy as heat energy,but also realize mild CO2 conversion under special photothermal conditions.The metals in group Ⅷ normally have good activity towards the catalytic hydrogenation of CO2.Especially,nickel-based catalysts attract widespread attention due to the advantage of low-cost.However,the application of nickel-based catalysts is restricted by its low activity and poor selection.In this work,an efficient Ni/CeO2 catalyst was developed through the synthesis of CeO2 nano-rods as substrate and the loading of nickel.This catalyst possessed good catalytic stability under photothermal process.Our research work mainly includes the following parts:We first used hydrothermal strategy to synthesize CeO2 with morphology of nano-rods.Nickel nano-particles were subsequently loaded onto the CeO2 substrate through impregnation method,Then the as-synthesized Ni/CeO2 was used as catalyst in the photothermal CO2 methanation and characterized by various methods such as XRD,BET,SEM,TEM,H2-TPR and CO2-TPD.In situ-FTIR and Raman techniques were also conducted to investigate the reaction mechanism.In the experiments,we found that the amount of nickel loading and reaction temperature affected the CO2 methanation.Results showed that the Ni/CeO2 with 12.5wt%Ni loading possessed-the best performance,and the CO2 conversion reached 99.5%with a high CH4 selectivity of 99%.In addition,the stability of catalysts is well maintained during long-time operation.We also compared the CO2 hydrogenation process in thermal and photothermal conditions.The conversion rate of CO2 in photothermal condition was significantly higher than that in pure thermal process.Finally,the inner mechanism for enhancement of CO2 methanation under photothermal condition was analyzed by the In situ-FTIR and Raman.Results indicated that CO was the key intermediate species for the conversion of CO2 to methane on Ni/CeO2 catalyst.CO2 molecules initially adsorbed on CeO2 to form CeO2*CO2,which then reacted H to produced CeO2*CO,.After that,the CO intermediate species was reduced further and converted into CH4.Under photothermal condition,the transformation of CO intermediate species was facilitated and a high conversion rate of CO2 to methane was finally achieved as a result.