Dynamic quantum molecular sieving separation of D2 from H2-D2 mixture with nanoporous materials.

Quantum molecular sieving separability of D(2) from an H(2)-D(2) mixture was measured at 77 K for activated carbon fiber, carbon molecular sieve, zeolite and single wall carbon nanotube using a flow method. The amount of adsorbed D(2) was evidently larger than H(2) for all samples. The maximum adsorption ratio difference between D(2) and H(2) was 40% for zeolite (MS13X), yielding a selectivity for D(2) with respect to H(2) of 3.05.

Photolysis of dibenzyl ketones sorbed on MFI zeolites in the presence of spectator molecules: cage effects, kinetics, and external surface sites characterization.

Over the past two decades, the photolytic reactions of dibenzyl ketones sorbed on zeolites have been investigated. The reported results are consistent with a supramolecular model that takes into account the physical and chemical nature of the structure of the zeolites and their effect on the reactive radical intermediates produced by photolysis of adsorbed molecules. The model incorporates various phenomena such as surface coverage, external and internal sorption, surface diffusion, radical sieving, and the resulting product distributions. This account reports direct evidence for the validation of the model through FT-IR spectroscopy and through a new method for "titrating" the binding sites via EPR spectroscopy. It is shown that it is possible to adjust and modulate the photolytic product distribution by varying the parameters of the system. The effects of co-adsorbed spectator molecules with different polarities, namely water, pyridine, and benzene, on the photolysis of o-methyldibenzyl ketone and dibenzyl ketone sorbed on MFI zeolites is examined. This study provides insights into a displacement mechanism caused by spectator molecules and further demonstrates how the product distribution of photolysis of sorbed ketones can be controlled. The kinetics of persistent radicals formed by photolysis of ketones sorbed on zeolites is directly monitored over time by EPR, providing a measure of the lifetime of these reactive organic intermediates. Finally, measurement of Langmuir isotherms was employed to provide classical evidence for the model.

EPR investigation of persistent radicals produced from the photolysis of dibenzyl ketones adsorbed on ZSM-5 zeolites.

Photolysis of ketones (1, 1-oMe, 2, 2-oMe, 3, and 4) adsorbed on ZSM-5 zeolites produces persistent carbon-centered radicals that can be readily observed by conventional steady-state EPR spectroscopy. The radicals are persistent for time periods of seconds to many hours depending on the supramolecular structure of the initial radical@zeolite complex and the diffusion and reaction dynamics of radicals produced by photolysis. The structures of the persistent radicals responsible for the observed EPR spectra are determined by a combination of alternate methods of generation of the same radical, by deuterium substitution, and by spectral simulation. A clear requirement for persistence is that the radicals produced by photolysis must either separate and diffuse from the external to the internal surface or be generated within the internal surface and separate and diffuse apart. The persistence of radicals located on the internal surface is the result of inhibition of radical-radical reactions. Radicals that are produced on the external surface and whose molecular structure prevents diffusion into the internal surface are transient because radical-radical reactions occur rapidly on the external surface. The reactions of the persistent radicals with oxygen and nitric oxide were directly studied in situ by EPR analysis. In the case of reaction with oxygen, persistent peroxy radicals are formed in high yield. The addition of nitric oxide scavenges persistent radicals and leads initially to a diamagnetic nitroso compound, which is transformed into a persistent nitroxide radical by further photolysis. The influence of variation of radical structure on transience/persistence is discussed and correlated with supramolecular structure and reactivity of the radicals and their parent ketones.