CHARACTERIZATION OF THE LEWIS-ACID SITES IN ZEOLITE HY WITH THE PROBEMOLECULE TRIMETHYLPHOSPHINE, AND P-31 AL-27 DOUBLE-RESONANCE NMR/

P-31/Al-27 TRAPDOR NMR is used to probe the binding of trimethylphosph ine on dehydroxylated zeolite HY. Three binding sites are observed at - 150 degrees C with P-31 isotropic chemical shifts of - 32, - 46 and - 60 ppm. Only the phosphine molecules resonating at - 46 ppm show lar ge TRAPDOR effects, demonstrating that these molecules are directly bo und to the aluminum Lewis acid sites. The phosphine molecules giving r ise to the resonance at - 32 ppm are, however, the most strongly bound to zeolite; phosphines bound to the other two sites are mobile at roo m temperature.