13C NMR study of propene as gas and in the adsorbed state on alkali metal-exchanged zeolites

The 13C chemical shifts, spin-lattice relaxation times and nuclear Overhauser enhancements have been recorded for propene in the gas phase and in the adsorbed state on Li+, Na+, K+, Cs+ and Rb+ cation-exchanged X and Y type zeolites. The chemical shifts in the adsorbed state are dependent on the degree of surface coverage but are relatively insensitive to the nature of the cation. The CH carbon shift in propene is influenced most by the adsorption process relative to the shifts in solution. The relaxation times of all carbons depend very much on the degree of propene loading and the concentration of Fe3+ ions in the zeolite (usually present as impurity) but only slightly on the nature of the cation. At Fe3+ contents greater than 200 ppm the relaxation process is dominated by the paramagnetic Fe3+; at lower Fe3+ levels two other contributions become important, namely C-H dipole-dipole interaction and spin-rotation interaction.