Yang J, Zheng A, Zhang M, Luo Q, Yue Y, Ye C, Lu X, Deng F. Brönsted and Lewis Acidity of the BF3/γ-Al2O3 Alkylation Catalyst as Revealed by Solid-State NMR Spectroscopy and DFT Quantum Chemical Calculations. J. Phys. Chem. B. 2005 Jun 18;109(27):13124–31. doi: 10.1021/jp051268l.