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DFT Cluster Modeling of Molecular and Dissociative Hydrogen Adsorption on Zn2+Ions with Distant Placing of Aluminum in the Framework of High-Silica Zeolites

“…Recently, we did this for the ZSM-5 zeolite with the Si/Al ratio of 25. All of the bridging hydroxyl groups were replaced in this case by the bivalent zinc ions via a high-temperature reaction with zinc vapor [7,8]. In agreement with the above discussion, this result should be considered as the first experimental evidence of the sitting of zinc cations in the zeolite framework at the single negative lattice charges created by the isolated aluminum atoms.…”

“…It is important that the calculations did not predict such strong perturbation owing to the adsorption of these molecules on binuclear ðZn-O-ZnÞ 2þ oxo-ions [10][11][12]. Our previous experimental study of hydrogen adsorption on Zn-and Co-loaded ZSM-5 zeolites also indicated that diffuse reflectance infrared Fourier transform (DRIFT) spectra of these molecules are surprisingly different from those adsorbed by the faujusites modified with the same cations [7,8,[13][14][15]. For instance, the H 2 adsorption by ZnHZSM-5 at 77 K results in the low-frequency shift of H-H stretching vibration equals to 220 cm À1 .…”

“…This is almost twice as large as the lowfrequency shift of H-H stretching frequency of 123 cm for hydrogen adsorbed by Zn 2þ ions at S II sites in the six-membered rings of the ZnY zeolite [16]. In addition, zinc-loaded ZSM-5 dissociatively adsorbs molecular hydrogen at room temperature [7,8,13,15], indicating the low activation energy of heterolytic dissociation due to extremely high chemical activity of zinc ions. In accordance with the above discussion, it was also found that the most strongly low-frequency-shifted bands of adsorbed hydrogen are observed for the zeolites with the very high Si/Al ratios, where the distant placing of aluminum ions is most probable.…”

Unusual Infrared Spectrum of Ethane Adsorbed by Gallium Oxide

“…[1][2][3] such new spectral approach was supported by our experimental results on adsorption of methane and ethane by ZSM-5 zeolite modified with Zn +2 cations. In these studies we demonstrated that, at elevated temperatures, the most intense C-H vibrations which correspond to the stretching of the highly polarized C-H bonds of molecules adsorbed by the coordinatively unsaturated zinc cations are involved into subsequent heterolytic dissociative adsorption via abstraction of protons by the adjacent basic oxygen atoms.…”

“…Therefore the beam path through the gas phase was limited to the void space within the catalyst bed, and gas phase contributions into IR spectra were minimized. Similar to our previous studies [1][2][3], DRIFT spectra were taken using a Nicolet "Impact 410" spectrophotometer equipped with a home-made diffuse reflectance attachment. CaF 2 powder was used for background measurements.…”