Solid-state NMR characterization of the acid sites in cubic mesoporous Al-MCM-48 materials using trimethylphosphine oxide as a 31P NMR probe

摘要: Abstract The acidic properties of Al-MCM-48 with Si/Al ratios ranging from 10 to 67, synthesized Gemini surfactant as the template, have been characterized by a combination multinuclear solid-state 1H, 23Na, 27Al, 29Si and 31P MAS (magic angle spinning) NMR some double-resonance methods using trimethylphosphine oxide (TMPO) probe molecule. XRD 27Al results indicated that aluminum has successfully incorporated into framework MCM-48 materials up Si/Al = 17.9 direct synthesis. 1H strongly supported generation Bronsted acid sites in cubic mesoporous material after incorporation aluminum, even without ion-exchange treatment. Double-resonance techniques such 31P/27Al TRAPDOR (Transfer Population Double Resonance) 29Si/31P REDOR (Rotational Echo were performed further correlate TMPO molecule silica framework. experiments at different temperatures able establish correlation between spins, confirms presence 65 ppm spectrum. Although assignment Lewis was somehow unambiguous NMR, FT-IR observation calcined samples adsorbed pyridine did reveal sites. In contrast pore size constraints zeolites, protonated highly mobile inside channels time scale.