Elucidating structure-performance correlations in gas-phase selective ethanol oxidation and CO oxidation over metal-dopedγ-MnO2  

金属掺杂γ-MnO2在乙醇气相选择氧化和CO氧化中的构效关系

作　　者：Panpan Wang Jiahao Duan Jie Wang Fuming Mei Peng Liu 王盼盼;段嘉豪;王杰;梅付名;刘鹏(华中科技大学化学与化工学院,能量转换与存储材料化学教育部重点实验室,材料化学与服役失效湖北省重点实验室,湖北武汉430074)

机构地区：[1]Key Laboratory of Material Chemistry for Energy Conversion and Storage(Ministry of Education),Hubei Key Laboratory of Material Chemistry and Service Failure,School of Chemistry and Chemical Engineering,Huazhong University of Science and Technology,Wuhan 430074,Hubei,China

出　　处：《Chinese Journal of Catalysis》2020年第8期1298-1310,共13页催化学报（英文）

基　　金：国家自然科学基金(21673088,21972050).

摘　　要：Despite of considerable efforts on the MnO2-based catalytic combustion,the different structural and component requirements of MnO2 for gas-phase selective oxidation and complete oxidation largely remain unknown.By comparing four types of MnO2 with different crystal structures(α,β,γandδ),γ-MnO2 was found to be the most efficient catalyst for both aerobic selective oxidation of ethanol and CO oxidation.The structural effect ofγ-MnO2 was further investigated by doping metal ions into the framework and by comparing the catalytic performance in the gas-phase aerobic oxidation of CO and ethanol.Among ten M-γ-MnO2 catalysts,Zn-γ-MnO2 showed the lowest temperature(160°C)for achieving 90%CO conversion.The CO oxidation activity of the M-γ-MnO2 catalysts was found to be more relevant to the surface acidity-basicity than the reducibility.In contrast,surface reducibility has been demonstrated to be more crucial in the gas-phase ethanol oxidation.Cu-γ-MnO2 with higher reducibility and more oxygen vacancies of Mn^2+/Mn^3+species exhibited higher catalytic activity in the selective ethanol oxidation.Cu-γ-MnO2 achieved the highest acetaldehyde yield(75%)and space-time-yield(5.4 g gcat^-1 h^-1)at 200°C,which are even comparable to the results obtained by the state-of-the-art silver and gold-containing catalysts.Characterization results and kinetic studies further suggest that the CO oxidation follows the lattice oxygen-based Mars-van Krevelen mechanism,whereas both surface lattice oxygen and adsorbed oxygen species involve in the ethanol activation.二氧化锰(MnO2)因具有制备简单、Mn^4+/Mn^3+/Mn^2+混合的金属价态、可调变的晶型结构(如α,β,γ,δ等)、丰富的表面氧缺陷和活泼的晶格氧等特点,在多相催化领域被广泛用作需氧氧化催化剂.MnO2催化气相氧化主要集中在催化燃烧或完全氧化,催化性能最佳的MnO2晶型因反应底物不同会有所差异.由于其氧化催化活性较高、选择性难于控制, MnO2这类结构丰富、价廉易得的催化剂在气相选择氧化制高附加值化学品中面临着机遇和挑战.乙醇气相选择氧化制乙醛符合绿色和可持续性化学工业的发展需求,被认为是替代传统高污染、高成本的乙烯瓦克氧化工艺的最佳选择.MnO2在催化乙醇燃烧中应用广泛,不同晶型MnO2中α-MnO2的活性最高.我们已经报道了非变价金属离子掺杂α-MnO2 (M-OMS-2),特别是具有最强表面碱性和可还原性的Na-OMS-2在乙醇气相选择氧化中获得了高达66%的乙醛产率和与贵金属催化剂相接近的催化效率.然而,不同晶型MnO2对乙醇气相选择氧化催化性能的影响,以及选择氧化和完全氧化所需的MnO2晶型和结构性质是否一致尚不清楚.这些问题的阐明无疑能够指导更高性能MnO2选择氧化催化剂的设计合成.本文首先制备了四种晶型(α,β,γ,δ)MnO2,并将其应用于气相乙醇选择氧化和CO氧化,惊喜地发现γ-MnO2在这两类反应中均表现出最高的催化活性,这与之前报道的乙醇催化燃烧和CO氧化结果明显不同,证明了MnO2的晶型结构和反应条件对其催化氧化性能有重要影响.为了深入研究γ-MnO2在乙醇气相选择氧化和CO氧化中的构效关系,通过一锅水热法制备了金属掺杂的M-γ-MnO2 (M=Cu^2+, Zn^2+, Mg^2+, Co^2+, Ni^2+, Ca^2+, Al^3+, Fe^3+, La^3+).采用多种表征手段证明了金属掺杂能够有效地调变γ-MnO2的结构组成、表面酸碱性和可还原性.制得的M-γ-MnO2催化剂在CO和乙醇氧化中显示出不同的活性顺序,

关 键 词：MNO2 Metal doping Ethanol oxidation ACETALDEHYDE Catalytic CO oxidation 

分 类 号：TQ224.124[化学工程—有机化工] TQ426