The Research Of NiMo Catalysts In CO₂ Reduction Reaction

The emission and accumulation of CO₂ caused sever environmental problems such as global warming and ocean acidification.CO₂ can be transformed into valuable chemicals such as CH₄ by methanation reaction or converted into CO via reverse water gas shift reaction,which provide feasible approaches to efficiently utilize CO₂.Ni-based catalysts are low cost and active in catalyzing CO₂ reduction,in this work,we demonstrated that the catalytic performance of CO₂ reduction over Ni-based catalysts can be tuned by doping different loading of Mo species.Addition of a small amount of Mo（Mo/Ni ratio of 0.1）is beneficial for CO₂ methanation reaction with the CH₄selectivity of 100%.In contrast,the addition of a large amount of Mo（Mo/Ni=1.0）shifts the reaction to RWGS selective with a CO selectivity of 94%.A series of characterization techniques（BET,XRD,H₂-TPR,TEM,XPS,FTIR）were applied for exploring the structure and properties of catalysts.The active component of reduced catalyst are metallic Ni and partially reduced Mo O_x.The strong interaction between Ni and Mo O_x species was determined that the presence of Ni promotes the reduction of Mo O_x,leading to the formation of O vacancies.For the low Mo loading catalyst（Mo/Ni ratio of 0.1）,the O vacancies on Mo O_x aids in the activation of both CO₂ and CO,thus the activity and selectivity toward methanation reaction are promoted.In turn,the reduced Mo O_x modifies the surface of Ni particles through both geometric coverage and electronic modification.To be specific,Mo O_x species help to disperse Ni particles and the coverage of Mo O_x to Ni was enhanced with the increasing of Mo loading.Besides,electron transferred from Ni to Mo O_x species,leading to the loss of electron density on Ni surface.For the high Mo loading catalyst（Mo/Ni ratio of1.0）,the coverage of Mo O_x to Ni and the electron loss of Ni sites altered the intrinsic properties of catalysts,leading to weak adsorption of CO,which was evidenced by the FTIR experiment that no CO adsorption was observed at room temperature.Therefore,the desorption of CO was facilitated.Tracking product evolution showed that CO₂ is first reduced to CO through RWGS on the Ni catalysts and CH₄ is a product of CO hydrogenation.Apparent activation energy analysis indicates that the overall reaction is controlled by CO desorption.