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.