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

Abstract

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 Brønsted acid sites on their external surfaces as well as in the internal micropore walls. The acid strength and concentration was characterized by the 31P NMR signals of the adsorbed trimethylphosphine oxide and tributylphosphine oxide. The 31P NMR investigation identified three types of Brønsted 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.