Characterization of the Lewis acid sites in zeolite HY with the probe molecule trimethylphosphine, and 31P/27Al double resonance NMR

31P/27Al TRAPDOR NMR is used to probe the binding of trimethylphosphine on dehydroxylated zeolite HY. Three binding sites are observed at −150°C with 31P isotropic chemical shifts of −32, −46 and −60 ppm. Only the phosphine molecules resonating at −46 ppm show large TRAPDOR effects, demonstrating that these molecules are directly bound to the aluminum Lewis acid sites. The phosphine molecules giving rise to the resonance at −32 ppm are, however, the most strongly bound to zeolite; phosphines bound to the other two sites are mobile at room temperature.