title: Brönsted and Lewis acidity of the BF3/gamma-Al2O3 alkylation catalyst as revealed by solid-state NMR spectroscopy and DFT quantum chemical calculations.
abstract: Multinuclear solid-state NMR techniques and DFT quantum chemical calculations were employed to investigate the detailed structure of acid sites on the BF3/gamma-Al2O3 alkylation catalyst. The NMR experiment results indicate that gaseous BF3 is able to react with the hydroxyl groups present on the surface of gamma-Al2O3, leading to the formation of new Brönsted and Lewis acid sites. The 1H/11B and 1H/27Al TRAPDOR (TRAnsfer of Population in DOuble Resonance) experiments suggest that the 3.7 ppm signal in 1H NMR spectra of the BF3/gamma-Al2O3 catalyst is due to a bridging B-OH-Al group that acts as a Brönsted acid site of the catalyst. On the other hand, a Lewis acid site on the surface of the catalysts, as revealed by 31P MAS and 31P/27Al TRAPDOR NMR of adsorbed trimethylphosphine, is associated with three-coordinate -OBF2 species. 13C NMR of adsorbed 2-13C-acetone indicates that the Brönsted acid strength of the catalyst is slightly stronger than that of zeolite HZSM-5 but still weaker than that of 100% H2SO4, which is in good agreement with theoretical prediction. In addition, DFT calculations also reveal the detailed structure of various acid sites formed on the BF3/gamma-Al2O3 catalyst and the interaction of probe molecules with these sites.
authors.affiliation: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, The Chinese Academy of Sciences, Wuhan 430071, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Anmin
authors.initials: A
authors.lastname: Zheng
authors.forename: Mingjin
authors.initials: M
authors.lastname: Zhang
authors.forename: Qing
authors.initials: Q
authors.lastname: Luo
authors.forename: Yong
authors.initials: Y
authors.lastname: Yue
authors.forename: Chaohui
authors.initials: C
authors.lastname: Ye
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Feng
authors.initials: F
authors.lastname: Deng