NH4F effect in post-synthesis treatment of Al-MCM-41 mesoporous materials

A series of Al-MCM-41 mesoporous molecular sieves, with Si/Al ratio in the range 15-40, were synthesized and characterized by XRD, N2 physisorption, DRIFT and 27Al and 29Si MAS NMR analysis. Al-MCM-41 samples were prepared by two procedures. (i) Synthesis at room temperature, following the procedure described by Grün et al. including some variations. (ii) The as-synthesized samples obtained in (i) were suspended in 300 mL of NH4F 0.1 M for 34 h. Al-MCM-41 samples with high surface acidity were synthesized. The NH4F treatment contributed to enhance these acidic properties, leading to materials highly active in the vaporphase cumene conversion, studied as a catalytic test. The catalytic activity was related to tetrahedral or octahedral aluminum environments for non-fluorinated samples and fluorinated ones, respectively.