Characterization of acidity in zeolites and related oxides using trimethylphosphine as a probe

摘要: The MAS-NMR spectra of trimethylphosphine (TMP) have been used to study acidity on zeolites, amorphous silica-alumina, sulfated ziconia and other solid materials. Acidic protons react with the strong Lewis base form [(CH3)3P-H]+ adducts that are characterized by a 31P chemical shift ca. -3 ppm JP-H coupling constant 500 Hz. Lewis-bound TMP exhibits resonances at considerably higher fields, if aluminum is involved, JP-Al 300 Hz may result in multiplet six lines. When excess present, rapid exchange occur between liquid-like molecules those complexed acid sites. In such cases distinction different forms obscured. Attempts relate Bronsted strength magnetic parameter as scalar show promise where majority species interest. dealuminated Y however, it appears small fraction responsible for acid-catalyzed reactions, value does not adequately reflect contribution these centers.