题目：Catalytic conversion of CO₂ to fuel

　　报告人：杨艳辉 教授（南京工业大学）

　　时间：1月15日（周一）10:00-11:30

　　地点：李薰楼249会议室

　　In the global attempt to reduce carbon footprint, the chemical and petrochemical industry faces the problem to replace the currently used fossil feedstock with renewable resources, reduce energy consumption and to intensify and integrate the processes to be more carbon efficient. In all three issues, catalysis will be the key to a successful transformation. Knowledge-based development and implementation of catalytic technology will help to process the novel feedstock, reduce the energy required for maintaining the desired process and improve the carbon efficiency of the targeted synthesis routes. In this seminar, two examples will be discussed to illustrate our efforts in the last year in CO₂ utilization.

　　The catalytic hydrogenation of CO₂ under atmospheric pressure is a hot topic in CO₂ utilization in which methanation and reverse water-gas shift (RWGS) serve two competing parallel pathways. Novel Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO₂. Adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst. The superior reactivity of monodentate formate towards hydrogenation than that of bidentate formate species was identified by DRIFTS analysis and the formation of more active monodentate formate species was indisputably facilitated by W additives, leading to the greatly enhanced catalytic activity. H2-TPR and CO₂-TPD characterization showed that doping W increased the number of stable CO₂ adsorption sites and helped in anchoring the Ni sites as a result of strengthened Ni-Mg interaction, both of which were responsible for the enhanced CO₂ methanation activity and the improved resistance against sintering.

　　The control mechanism of catalytic selectivity and structure-activity relation at atomic scale need further understanding. It has been suggested that the dispersion state and the size of metallic particles play a crucial role in determining CO₂ conversion and selectivity as well as stability. However, these studies have not considered the possible effect of interface sites between metal and oxide support in selective hydrogenation of CO₂. In this work, three structural configurations of monolayer, periphery and nanocluster in Ru/Al₂O₃ catalysts were obtained by control of Ru weight loadings, confirmed by the characterization results of the extended X-ray absorption fine structure, H₂-O₂ titration and diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption. The kinetic data reveal the dependence of reaction rates for CO and CH4 formation with different apparent activation energies on the Ru surface structures. Theoretical calculations of Ru₉/Al₂O₃ and Ru₃₅/Al₂O₃ models demonstrate that monolayer Ru sites favor the RWGS route with a relatively low energy barrier for both CO₂ activation and CO formation steps, while Ru nanoclusters prefer methanation route energetically. Moreover, the combination of theoretical calculations and experimental isotope-exchange measurements suggests that the interfacial O species in Ru-Al₂O₃ interfaces act a critical role in CO₂ activation via exchanging with O atom in feeding CO₂ and incorporating into the final hydrogenation products.