Search

Abstract: Molecular simulations were used to screen a diverse collection of eight homochiral metal–organic frameworks (MOFs) for their ability to separate 19 chiral compounds by enantioselective adsorption. The simulation model was validated by comparison with available experimental data. It was found that high enantioselectivity is strongly correlated with a close match between the size of the pore and the size of the chiral sorbate molecule. However, there is also a possibility of no enantioselectivity even when the size of the pore matches with the size of the chiral sorbate molecule. A four-point model was used to explain this observation, and a solution to promote high enantioselectivity has been proposed. [Copyright &y& Elsevier]

Abstract: The three-point model and molecular simulation are used to understand the enantioselective adsorption of a homologous series of chiral compounds on a common chiral selector that is incorporated on a solid surface. We demonstrate how the enantioselectivity of homologous chiral compounds may go down, go up, remain the same, or even reverse. Conditions that lead to consistent enantioselectivity for homologous chiral compounds are also proposed. [Copyright &y& Elsevier]

Abstract: Grand canonical Monte Carlo simulations have been carried out to investigate the adsorption of water from the vapor phase into the zeolite silicalite. For truly hydrophobic micropores, the simulations predict essentially no adsorption of water at low pressures, followed by rapid pore filling as pressure is increased. The effect of silanol defects in real silicalite samples was explored through simulations using “seeded” water molecules to represent hydrophilic defects. These defects promote adsorption of some water at low pressures, as molecules form hydrogen-bonded clusters around the defects. The defects also shift the pore filling to a lower pressure than in the completely hydrophobic material. [Copyright &y& Elsevier]

The extraframework locations of many metal cations in pentasil zeolites, such as ferrierite, are not known, but new infrared bands in the 800–1000 cm−1 region are experimentally observed upon exchange. To investigate the origin of these bands and to better understand cation siting, density functional theory calculations were performed on ferrierite cluster models for seven divalent metals: magnesium, manganese, iron, cobalt, nickel, copper, and zinc. The calculated properties, such as the metal–zeolite binding energy, follow a U-shaped trend with respect to the number of metal d electrons. The calculated infrared bands are consistent with the occupation of the B and G ferrierite sites by the metal cations. However, a definitive assignment of the published experimental infrared bands to particular extraframework sites was not possible. Despite this limitation, all seven metals were shown to perturb the ferrierite framework similarly. All of the cations coordinate to four framework oxygen atoms and the framework T–O bonds associated with these oxygen atoms are elongated by the metal. This elongation is shown to be proportional to the wavenumber of the infrared bands. [Copyright &y& Elsevier]

A novel MCM-41-supported base catalyst, Ba-MCM-41, was synthesized with a modified impregnation method. Ba2SiO4 was synthesized on the MCM-41 pore wall as confirmed by characterization using X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence, N2 adsorption, 29Si MAS NMR and transmission electron microscopy. It was also demonstrated that a highly ordered Ba-MCM-41 catalyst with high barium loading (4.1–25.2 wt.%) and dispersion was obtained using this method. The basicity of the catalyst, which was characterized according to the binding energy of O 1s, was increased with increasing amounts of barium in the catalyst. [Copyright &y& Elsevier]