The Role of Silanols in the Interactions between Methyl <i>tert</i>-Butyl Ether and High-Silica Faujasite Y: An Infrared Spectroscopy and Computational Model Study

It is generally believed that the retention of methyl <i>tert</i>-butyl ether (MTBE) by zeolites is positively correlated to the silica content of these materials. Nevertheless, highly dealuminated zeolites can contain relevant amounts of silanol groups. In this study, the effect of these point defects in a zeolite Y (SiO₂/Al₂O₃ = 200) on the adsorption of MTBE was evaluated by means of infrared spectroscopy, supported by DFT calculations. The adsorption process is found to occur in two steps, involving isolated silanol sites and the siloxane network of the zeolite, respectively, with an average loading of 1.3 molecules per cage in the first and 1.3 molecules in the second stage. Both external and internal isolated silanol groups (stretching at 3746 and 3738 cm^–1, respectively) are involved in the MTBE adsorption process with the formation of H-bonded complexes and associated shifts (516 and 358 cm^–1, respectively), consistent with a H-bonding strength higher for external than for the internal ones. However, MTBE is more tightly adsorbed on the internal silanols as a result of the cage confinement effect. The band assigned to the methyl symmetric stretching of the CH₃O– group can be used to discriminate between H-bond and van der Waals MTBE–zeolite interactions (2843 and 2828 cm^–1, respectively). Ab initio models were used to compute the harmonic frequencies of different MTBE–zeolite models and to simulate the cage confinement of one and three ether molecules

On the Intercalation of the Iodine–Iodide Couple on Layered Double Hydroxides with Different Particle Sizes

Molecular iodine was intercalated from nonaqueous solution into microsized ZnAl-layered double hydroxide (LDH) in the iodide form, generating the I₃^–/I^– redox couple into the interlayer region. Chloroform, ethanol, acetonitrile, or diethyl ether were used as solvents to dissolve the molecular iodine. The intercalation compounds were characterized by thermogravimetric analysis, X-ray powder diffraction, UV–vis spectroscopy, and scanning and transmission electron microscopy. The stability of iodine–solvent adducts and the iodine concentration affected the LDH iodine loading, and samples with I₂/I^– molar ratio ranging from 0.14 to 0.82 were prepared. Nanosized, well dispersible LDH, synthesized by the urea method in water–ethylene glycol media, were also prepared and successfully functionalized with the I₃^–/I^– redox couple applying the conditions optimized for the micrometric systems

The Role of Silanols in the Interactions between Methyl <i>tert</i>-Butyl Ether and High-Silica Faujasite Y: An Infrared Spectroscopy and Computational Model Study

It is generally believed that the retention of methyl <i>tert</i>-butyl ether (MTBE) by zeolites is positively correlated to the silica content of these materials. Nevertheless, highly dealuminated zeolites can contain relevant amounts of silanol groups. In this study, the effect of these point defects in a zeolite Y (SiO₂/Al₂O₃ = 200) on the adsorption of MTBE was evaluated by means of infrared spectroscopy, supported by DFT calculations. The adsorption process is found to occur in two steps, involving isolated silanol sites and the siloxane network of the zeolite, respectively, with an average loading of 1.3 molecules per cage in the first and 1.3 molecules in the second stage. Both external and internal isolated silanol groups (stretching at 3746 and 3738 cm^–1, respectively) are involved in the MTBE adsorption process with the formation of H-bonded complexes and associated shifts (516 and 358 cm^–1, respectively), consistent with a H-bonding strength higher for external than for the internal ones. However, MTBE is more tightly adsorbed on the internal silanols as a result of the cage confinement effect. The band assigned to the methyl symmetric stretching of the CH₃O– group can be used to discriminate between H-bond and van der Waals MTBE–zeolite interactions (2843 and 2828 cm^–1, respectively). Ab initio models were used to compute the harmonic frequencies of different MTBE–zeolite models and to simulate the cage confinement of one and three ether molecules

Interactions of Toluene and <i>n</i>‑Hexane on High Silica Zeolites: An Experimental and Computational Model Study.

The knowledge of host–guest interactions occurring in confined space between porous solids and embedded molecules of different origin is an important task to improve adsorption properties of materials, thus extending their application fields. In this work, the interactions of toluene and <i>n</i>-hexane molecules (selected as models of organic pollutants coming from industrial waste of oil refineries and gas stations) on different dealuminated high silica zeolites were studied by means of both experimental and computational approaches. Zeolites with different textural and surface features were selected as adsorbents and the effect of their physicochemical properties (i.e., pore size architecture and type and amount of surface OH sites) on sorption capacity were studied. High silica Y and ZSM-5 zeolites (with a SiO₂/Al₂O₃ ratio of 200 and 280, respectively) were selected as model sorbents. FTIR and SS-NMR spectroscopy were used to study the type and strength of the host−guest interactions between the molecules and the zeolite surface. Gravimetric analysis allowed the determination of the sorption capacity of both zeolites and their affinity to pollutants. The interactions between the silica surfaces and pollutants molecules computed at the DFT level, and supplemented by empirical formulation of dispersion energies, led to estimate the intensity of hydrogen bonding and cooperative van der Waals interactions