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 temperature (5 K) diffraction measurements reveal that benzene is located both above the six-ring window and in the plane of the 12-ring window and that protons are found only at O(2) where a facial interaction with adsorbed benzene can occur. The results indicate that the acid sites are redistributed under the influence of the sorbate in order to enhance the proton-benzene interactions at the six-ring site. Variable temperature 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 may 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.