Siting of mixtures in mordenite zeolites: F-19 and Xe-129 NMR and molecular simulation

and Xe-129 nuclear magnetic resonance spectroscopy (NMR) investigations wer e performed to validate predictions from Monte Carlo simulations for molecu lar siting in mordenite zeolites. For single-component adsorption, CF4 adso rbs preferentially in the mordenite main channel, while Xe adsorbs about eq ually in the main channel and the mordenite side pocket. The. temperature a nd pressure dependences of the siting were studied, as well as the influenc e of zeolite cation exchange on molecular siting;. Xe-129 NMR studies of Xe -CF4 binary mixtures in Na-mordenite show that the main channel peak decrea ses with increasing concentration of CF4, implying that Xe prefers the side pocket while CF4 prefers, the main channel in the binary system. Results s how that F-19 NMR of adsorbed CF4 can be used to characterize different zeo lite environments in a manner similar to Xe-129 NMR but with reduced sensit ivity. The NMR results provide a stringent test of molecular simulation of adsorption by providing molecular-level siting that complements macroscopic experimental quantities such as the adsorption isotherm and heat of adsorp tion. Simultaneously predicting siting and macroscopic quantities is a diff icult challenge for simulation. To improve the molecular model, an explicit polarization term was added to the usual Lennard-Jones potential.