Acidity characterization of MCM-41 materials using solid-state NMR spectroscopy

摘要

A comprehensive study has been made on the acid properties of the mesoporous H-AlMCM-41 molecular sieves with varied Si/Al ratios using solid-state NMR techniques, namely by ~(31)P MAS NMR of the adsorbed trimethylphosphine and trimethylphosphine oxide probe molecules in conjunction with elemental analysis. As the consequence of such combined techniques, which rendered not only qualitative (types and strengths) but also quantitative (concentrations) determinations of acid sites, one type of Lewis acid site and two different Bronsted acid sites were identified for H-AlMCM-41. Furthermore, based on the results obtained from ~1H and ~(27)Al MAS NMR of the species associated with structural frameworks, possible formation mechanisms for various acid sites were also proposed.