Comparative study of the strongest solid Lewis acids known: ACF and HS-AlF3Dedicated to Prof. Dietmar Stalke on the occasion of his 60th birthday.Electronic supplementary information (ESI) available. See DOI: 10.1039/c8dt03279c

• Main Authors: Calvo, Beatriz, Marshall, Clara Patricia, Krahl, Thoralf, Kröhnert, Jutta, Trunschke, Annette, Scholz, Gudrun, Braun, Thomas, Kemnitz, Erhard
• Format: Journal Article
• Language: English
• Published: 27.11.2018
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt03279c

Aluminium chlorofluoride (ACF) and high-surface aluminium fluoride ( HS -AlF 3 ) were analyzed by a set of characterization methods to assess their acidic properties: NH 3 -TPD, CO adsorption followed by DRIFTS, CD 3 CN-PAS-FTIR and MAS NMR spectroscopy after 15 N-pyridine adsorption. Both catalysts contain very strong and medium-strong Lewis acid sites as confirmed by CO adsorption, in which small differences arise from the morphological properties of each catalyst, with ACF being microporous and HS -AlF 3 mesoporous. Shifts of the CO vibration band of up to 77 cm −1 were observed, which account for very strong Lewis acid sites. In addition, very strong Lewis acid sites could be identified by CD 3 CN-PAS for both catalysts, exhibiting a shift of 95 cm −1 from free nitrile, the highest ever reported for a solid Lewis acid. Aluminium chlorofluoride (ACF) and high-surface aluminium fluoride ( HS -AlF 3 ) can be considered as solid superacids based on several surface characterization techniques presented here.