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    Atomically dispersed zeolite-supported rhodium complex: Selective and stable catalyst for acetylene semi-hydrogenation
    (Elsevier, 2024) Kurtoğlu-Öztulum, Samira Fatma; Zhao, Yuxin; Hoffman, Adam S.; Uzun, Alper; Demircan, Oktay; Yordanli, Melisa Su; Hong, Jiyun; Perez-Aguilar, Jorge E.; Saltuk, Aylin; Akgül, Deniz; Ateşin, Tülay A.; Aviyente, Viktorya; Gates, Bruce C.; Bare, Simon R.
    Supported rhodium catalysts are known to be unselective for semi-hydrogenation reactions. Here, by tuning the electronic structure of supported mononuclear rhodium sites determined by the metal nuclearity and the electron-donor properties of the support, we report that atomically dispersed HY zeolite-supported rhodium with reactive acetylene ligands affords a stable ethylene selectivity > 90 % for acetylene semi-hydrogenation at 373 K and atmospheric pressure, even when ethylene is present in a large excess over acetylene. Infrared and X-ray absorption spectra and measurements of rates of the catalytic reaction complemented with calculations at the level of density functional theory show how the catalyst performance depends on the electronic structure of the rhodium, influenced by the support as a ligand that is a weak electron donor.
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    Photophysical, kinetic and thermodynamic study of one-component Type II thioxanthone acetic acid photoinitiators
    (Pergamon-Elsevier Science Ltd, 2020) Metin, Eyüp; Arsu, Nergis; Çatak, Şaron; Aviyente, Viktorya
    In this study, One-Component Type II thioxanthone acetic acid based photoinitiators, as well as the conventional Type II photoinitiator with phenyl acetic acid based co-initiators, have been investigated in terms of their photophysical, kinetic and thermodynamic properties by a series of Density Functional Theory (DFT) calculations. Experimental UV-Vis spectra have been compared with computationally generated UV-Vis spectra via Time-Dependent DFT (TD-DFT) and by taking into consideration the vibrational and dynamic effects (Wiggler). Natural transition orbitals have been generated for thioxanthone acetic acid derivatives to understand the physical nature of electronic transitions. Furthermore, kinetic and thermodynamic parameters of radical attack to the monomer of thioxanthone acetic acid based radicals and phenyl acetic acid based co-initiator radicals have been investigated. Comparison of the thermodynamic parameters of the initiating radicals has shown that initiation is more favorable with exocyclic radicals in both cases. Exocyclic radicals of the thioxanthone acetic acid derivatives and phenyl acetic acid derivates have been found to have comparable activation energies for their attack to methyl methacrylate. Furthermore, the spin densities and the radical Fukui functions of the attacking radicals have been nicely correlated with the activation barriers. In this way, a fast and predictive approach for the determination of radical reactivity in photopolymerization reactions has been proposed; this enables the evaluation of the initiation efficiency of the photoinitiators prior to synthesis.