Characterization of the Surface Acidity of MFI Zeolite Nanosheets by 31P NMR of Adsorbed Phosphine Oxides and Catalytic Cracking of Decalin

MFI zeolite nanosheets tailored to 2.5-nm thickness were synthesized using a surfactant-type zeolite structure-directing agent, [C22H45-N+(CH3)(2)-C6H12-N(CH3)(2)-C6H13](Br-)(2). The zeolite nanosheets possessed Bronsted acid sites on their external surfaces as well as in the internal micropore walls. The acid strength and concentration was characterized by the P-31 NMR signals of the adsorbed trimethylphosphine oxide and tributylphosphine oxide. The P-31 NMR investigation identified three types of Bronsted acid sites with different strengths on external surfaces; there were four types inside the micropores. A linear correlation has been established between the number of the external strongest acid sites and the catalytic activity in decalin cracking for the MFI zeolite catalysts investigated in this work.