Adsorption of cyclic ketones on the external and internal surfaces of a faujasite zeolite (CaX).: A solid-state 2H NMR, 13C NMR, FT-IR, and EPR investigation

The adsorption characteristics (binding distributions, location, interactions, supramolecular structures, kinetics) of two cyclic ketones, 2-phenylcyclododecanone (1(12)) and 2-phenylcydopentadecanone (1(15)) onto the faujasite zeolite CaX have been investigated by a combination of spectroscopic techniques (H-2 NMR, EPR, C-13 NMR, IR), This approach allows a detailed description of the supramolecular structure of the ketone@CaX complexes, the time dependence of exchange between binding sites, and the interactions of the ketones with coadsorbed molecules on the external and internal surface of CaX. It was found that, at room temperature, the smaller ketone, 112, readily enters the internal zeolite surface, whereas the larger ring ketone, 1(15), initially resides on the external surface but is adsorbed slowly into the internal surface. The results demonstrate that both 1(12) and its undergo a significant loss of mobility upon entering the CaX internal surface. Coadsorption of 112 and benzene into CaX results in a decrease in the mobilities of both II and benzene due to the fact that both benzene and lit are adsorbed in the same supercage. On the contrary, it was found that 112 molecules negligibly perturbed the adsorption of nitroxide radicals, which are adsorbed exclusively on the external CaX surface. 1(15), which is initially adsorbed mainly at the external zeolite surface, undergoes progressive adsorption into the internal surface, which is accelerated by sample heating and increased loading. Coadsorption of 115 and benzene to CaX forces benzene molecules to aggregate in the supercages, because the benzene and Its molecules in the internal surface cannot share the same supercage due to the large size of the 115 molecules. 115 also causes the aggregation of nitroxides that are adsorbed on the external surface. However, as 115 is adsorbed into the internal surface of CaX, the nitroxides deaggregate on the external surface sites. Radical scavenging of nitroxides adsorbed on the external surface of CaX occurred upon photolysis of 1(15)@CaX but not upon photolysis of 1(12)@CaX. The results are consistent with the model employed for the interpretation of the photochemistry of 1(12)@CaX and 1(15)@CaX.