High population and dispersion of pentacoordinated Al~Ⅴ species on the surface of ?ame-made amorphous silica-alumina

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英文篇名：High population and dispersion of pentacoordinated Al~Ⅴ species on the surface of ?ame-made amorphous silica-alumina 作者：Zichun ; Wang ; Yijiao ; Jiang ; Xianfeng ; Yi ; Cuifeng ; Zhou ; Aditya ; Rawal ; James ; Hook ; Zongwen ; Liu ; Feng ; Deng ; Anmin ; Zheng ; Michael ; Hunger ; Alfons ; Baiker ; Jun ; Huang 英文作者：Zichun Wang;Yijiao Jiang;Xianfeng Yi;Cuifeng Zhou;Aditya Rawal;James Hook;Zongwen Liu;Feng Deng;Anmin Zheng;Michael Hunger;Alfons Baiker;Jun Huang;School of Chemical and Biomolecular Engineering & Sydney Nano Institute, The University of Sydney;Department of Engineering, Macquarie University;State Key Laboratory Magnetic Resonance & Atomic Molecular Physics, Wuhan Institute of Physics & Mathematics, Chinese Academy of Sciences;Mark Wainwright Analytical Centre, University of New South Wales;Institute of Chemical Technology, University of Stuttgart;Department of Chemistry and Applied Bioscience, ETH Zürich; 英文关键词：Amorphous silica-alumina;;Pentacoordinated Al~Ⅴ species;;~(27)Al multiple quantum magic-angle-spinning NMR;;H/D exchange 中文刊名：JXTW 英文刊名：科学通报(英文版) 机构：School of Chemical and Biomolecular Engineering & Sydney Nano Institute, The University of Sydney;Department of Engineering, Macquarie University;State Key Laboratory Magnetic Resonance & Atomic Molecular Physics, Wuhan Institute of Physics & Mathematics, Chinese Academy of Sciences;Mark Wainwright Analytical Centre, University of New South Wales;Institute of Chemical Technology, University of Stuttgart;Department of Chemistry and Applied Bioscience, ETH Zürich; 出版日期：2019-04-30 出版单位：Science Bulletin 年：2019 期：v.64 基金：the financial supports by Australian Research Council Discovery Projects (DP150103842);; Discovery Earlier Career Research Project (DE190101618);; the Faculty's MCR Scheme, Energy and Materials Clusters at the University of Sydney;; the support by the National Natural Science Foundation of China (21522310, 21473244 and 21210005) 语种：英文; 页：JXTW201908009 页数：8 CN：08 ISSN：10-1298/N 分类号：36-43

摘要

Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely observed in conventionally prepared silica-alumina.Here,we show that high population and dispersion of Al~Ⅴ species on the surface of amorphous silica-alumina(ASA)can be achieved by means of flame spray pyrolysis.High resolution TEM/EDX,high magnetic-field NMR and DFT calculations are employed to characterize the structure of as-prepared ASAs.Solid-state ~(27)Al multi-quantum MAS NMR experiments show that most of the Al~Ⅴspecies are formed independently from the alumina phase and are accessible for guest molecules on the surface.Upon water adsorption,these Al~Ⅴ species are transformed to Al~Ⅵ species,structurally similar to surface Al~Ⅳ species,as confirmed by DFT calculations.The outstanding catalytic activity of as-synthesized ASA is demonstrated using the in situ H/D exchange reaction with deuterated benzene as an example.The Al~Ⅴ-rich ASA provides a much lower activation energy(～30 kJ/mol)than that reported for zeolite H-ZSM-5(～60 kJ/mol).The superior catalytic performance is attributed to the high Al~Ⅴcontent promoting the surface active sites in ASA.The knowledge gained on the synthesis of Al~Ⅴ-rich ASAs and the nature of aluminum coordination in these materials could pave the way to more efficient silica-alumina based catalysts.
        Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely observed in conventionally prepared silica-alumina.Here,we show that high population and dispersion of Al~Ⅴ species on the surface of amorphous silica-alumina(ASA)can be achieved by means of flame spray pyrolysis.High resolution TEM/EDX,high magnetic-field NMR and DFT calculations are employed to characterize the structure of as-prepared ASAs.Solid-state ~(27)Al multi-quantum MAS NMR experiments show that most of the Al~Ⅴspecies are formed independently from the alumina phase and are accessible for guest molecules on the surface.Upon water adsorption,these Al~Ⅴ species are transformed to Al~Ⅵ species,structurally similar to surface Al~Ⅳ species,as confirmed by DFT calculations.The outstanding catalytic activity of as-synthesized ASA is demonstrated using the in situ H/D exchange reaction with deuterated benzene as an example.The Al~Ⅴ-rich ASA provides a much lower activation energy(～30 kJ/mol)than that reported for zeolite H-ZSM-5(～60 kJ/mol).The superior catalytic performance is attributed to the high Al~Ⅴcontent promoting the surface active sites in ASA.The knowledge gained on the synthesis of Al~Ⅴ-rich ASAs and the nature of aluminum coordination in these materials could pave the way to more efficient silica-alumina based catalysts.

引文

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