Dynamics of Benzene Adsorbed on Ca-LSX Zeolite Studied by Solid-State Two-Dimensional Exchange ~(13)C NMR

摘要

Transport of molecular guest species in confined environments is central to the performance of many permeable materials, including porous catalysts, adsorbents, membranes, and polymers, which are heterogeneous systems characterized by appreciable disorder and complexity. Neutron and X-ray diffraction investigations can provide local structural information for guest configurations that possess sufficiently long range periodic order, while complementary structural measurements over much shorter length scales are provided by nuclear magnetic resonance (NMR) techniques. Information on local guest species dynamics, however, is often difficult to infer from such studies, although over longer length scales (ca. 1 μm) molecular self-diffusion can be measured by means of pulsed-field-gradient NMR methods. Solid-state two-dimensional (2D) exchange NMR strategies pioneered by Spiess and co-workers for studying reorientation geometries and time scales of slow dynamic processes in polymers are powerful probes of local environment and dynamics. We report here the first solid-state ~(13)C NMR measurement of analogous transport dynamics of adsorbed hydrocarbon guest molecules on a microporous molecular sieve, specifically, benzene adsorbed on Ca-LSX zeolite.