Diphosphine probe molecules and solid-state NMR investigations of proximity between acidic sites in zeolite HY

The proximity between acidic sites in zeolite HY with different n(Si)/n(Al) ratios was investigated by applying 31P MAS NMR and diphosphine probe molecules, with two phosphorous atoms that can bind to two nearby acidic sites. By careful analyses of NMR spectra of samples with appropriate loading levels, the fractions of species which are connected to two/one/zero acidic sites were determined. The results presented suggest that there are no acidic clusters in the high Si/Al-content zeolite HY samples investigated in this study.