CO2氧化乙苯脱氢高效钒基催化剂构筑及反应机理研究

In comparison with the industrial process for the production of styrene, i.e., the catalytic dehydrogenation of ethylbenzene in the presence of overheated steam, the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO2-ODEB) is characterized in high efficiency, energy-saving, and effective utilization of the greenhouse gas of CO2. However, the severe deactivation of reported catalysts is a bottleneck for the industrialization of CO2-ODEB. Based on our understanding of the reaction and preliminary promising results, in this project, an idea on the design of high-performance vanadia based catalyst, which the redox cycle of Ce3+-Ce4+ is utilized to inhibit the deep reduction of V5+, is proposed, and V2O5/(-)Ce-ZrO2-Al2O3 catalyst will be prepared by different methods. By using the steady and dynamic reaction techniques and the relevant characterization methods such as in situ FTIR, the following work related to the titled reaction and the catalyst will be carried out, i.e., the kinetic behavior and modes for the adsorption, activation, and reaction of the reactants over the catalyst surface; the composition and structure of the catalytic active centers and their transformation behavior with increasing time on stream (TOS); the inhibiting mechanism of Ce3+-Ce4+ redox on the deep reduction of V5+ and the impact induced from the CO product; the deposition of the carbonaceous species over the catalyst and its compositional and structural changing pattern with increasing TOS. By analyzing and correlating the obtained results, the intrinsic kinetics equations of CO2-ODEB over the catalyst will be obtained, and the key factors influencing the stability of the catalyst will be revealed. Moreover, a detailed reaction mechanism for CO2-ODEB can be reasonably expected. Following the proposed reaction mechanism, a reasonable catalyst model for CO2-ODEB will be developed, leading to an optimal catalyst with a high activity and stability for the titled reaction. The achievement of the project will lay a foundation for the development of a high-performance vanadia based catalyst for the commercialization of CO2-ODEB.

与乙苯直接脱氢制苯乙烯工业过程相比，CO2氧化乙苯脱氢具有高效、节能和温室气体高效利用的突出优势，但催化剂失活严重是限制其工业化应用的瓶颈。本项目针对CO2氧化乙苯脱氢高活性钒基催化剂快速失活的难题，提出利用Ce3+-Ce4+的氧化还原循环抑制V5+深度还原的催化剂设计思想，并构筑V2O5/(-)Ce-ZrO2-Al2O3催化剂。采用稳态和动态反应技术及原位红外光谱等手段，研究反应物分子在催化剂表面的活化和转化机制及动力学行为、催化活性中心的形成及其演变规律、Ce3+-Ce4+的氧化还原循环对V5+深度还原的抑制作用机理及其与产物CO还原行为的匹配机制、催化剂表面积碳物种的形成及其结构演变规律，获得本征动力学方程，揭示催化剂失活机制，阐明反应机理。在此基础上，构建相应的催化剂模型，为优化设计催化剂提供理论依据，获得高活性和高稳定性CO2氧化乙苯脱氢催化剂，为该绿色工艺的工业化应用奠定基础。

与乙苯直接脱氢制苯乙烯工业过程相比，CO2氧化乙苯脱氢具有高效、节能和温室气体有效利用的突出优势，但现有催化剂普遍失活严重，成为该绿色过程工业化应用的瓶颈。针对高活性钒基CO2氧化乙苯脱氢催化剂快速失活的难题，本项目提出了利用Ce3+/Ce4+的氧化还原循环抑制V5+深度还原的催化剂设计思想。为此，分别采用溶胶凝胶法、水热法、溶剂蒸发诱导自组装法、燃烧分解法和原子层沉积法制备了一系列V2O5/(-)CexZr(1-x)O2-Al2O3催化剂，采用XRD、XPS、TEM、Raman、UV-vis、H2-TPR和低温N2吸附等方法，研究了上述催化剂的结构、织构、还原行为等性能；采用稳态和动态反应技术，考察了其催化CO2氧化乙苯脱氢的动力学行为；采用XRD、XPS、Raman、TG-DSC等研究了反应后催化剂的结构、积炭等特点。结果表明，CexZr(1-x)O2的加入显著提高了V2O5/(-)Al2O3催化剂的稳定性，其中ZrO2的作用在于稳定CeO2的晶格结构；V2O5和CexZr(1-x)O2的结构、结晶度及其在Al2O3表面的分布显著影响V2O5/(-)CexZr(1-x)O2-Al2O3催化剂的稳定性；钒氧化物催化CO2氧化乙苯脱氢反应符合氧化还原机理，且单（多）聚态钒氧化物中的V-O-Al极可能是其活性中心；富缺陷位、高分散的CexZr(1-x)O2通过Ce3+/Ce4+的氧化还原循环抑制了V5+的深度还原，且其抑制程度与V2O5和CexZr(1-x)O2的界面接触面积呈正相关，是决定V2O5/(-) CexZr(1-x)O2-Al2O3稳定性的关键因素；催化剂表面积炭并不是催化剂失活的关键因素，其中类石墨碳导致了催化剂的可逆失活。根据上述结果，提出了负载钒氧化物催化CO2氧化乙苯脱氢的反应机理，获得了具有工业应用价值的高性能钒基催化剂，为该绿色过程的产业化奠定了基础。