THE INTERACTION OF SORBATES WITH ACID SITES IN ZEOLITE CATALYSTS - A POWDER NEUTRON-DIFFRACTION AND H-2 NMR-STUDY OF BENZENE IN H-SAPO-37

The structure of perdeuterobenzene adsorbed in zeolitic H-SAPO-37 has been studied by powder neutron diffraction and H-2 NMR. Low temperatur e (5 K) diffraction measurements reveal that benzene is located both a bove the six-ring window and in the plane of the 12-ring window and th at protons are found only at O(2) where a facial interaction with adso rbed benzene can occur. The results indicate that the acid sites are r edistributed under the influence of the sorbate in order to enhance th e proton-benzene interactions at the six-ring site. Variable temperatu re H-2 spin-lattice relaxation measurements show that the diffusion of benzene in H-SAPO-37 is intermediate between those in Na-Y (Si/Al = 1 .7) and siliceous Y bur is very similar to those in H-Y and US-Y. We m ay also infer from the H-2 NMR data that the benzene participates in a facial interaction with the protons at O(2) at low temperatures.