Sooknoi, Tawan

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Sooknoi, Tawan
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Sooknoi, T.
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tawan.so@kmitl.ac.th

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    Catalytic deoxygenation of benzaldehyde over gallium-modified ZSM-5 zeolite
    (2009-11-15)
    Ausavasukhi, Artit
    ;
    Sooknoi, Tawan
    ;
    Resasco, Daniel E.
    The deoxygenation of benzaldehyde has been investigated over gallium-modified ZSM-5 catalysts. In the absence of H<inf>2</inf>, Ga/HZSM-5 catalyzes benzaldehyde decarbonylation resulting in benzene and CO. The active sites for this reaction are the strong Brønsted acid sites. In the presence of H<inf>2</inf>, the main product is toluene. It is believed that Ga cationic species (Ga<sup>+</sup> / GaH<inf>2</inf><sup>+</sup>) generated during H<inf>2</inf> reduction can promote the hydrogenation/hydrogenolysis reactions that give toluene and water. In the absence of H<inf>2</inf>, toluene can only be observed in transient experiments when the Ga/HZSM-5 catalysts are reduced. It is suggested that the GaH<inf>2</inf><sup>+</sup> species generated under H<inf>2</inf> play an important role in the hydrogenation/hydrogenolysis. However, they readily decompose to Ga<sup>+</sup> in the absence of H<inf>2</inf>. The addition of water to the feed modifies the catalytic activity and selectivity of Ga/HZSM-5 catalysts. On the one hand, water generates additional Brønsted acid sites from the reaction of extra-framework Ga with chemisorbed water (GaO(OH)) and with defect hydroxyls of the zeolite framework (GaOHSi). These additional sites enhance the production of benzene but decrease the production of toluene, due to a decrease in the density of reduced Ga cationic species. © 2009 Elsevier Inc. All rights reserved.
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    Tunable activity of [Ga]HZSM-5 with H2 treatment: Ethane dehydrogenation
    (2014-01-01)
    Ausavasukhi, Artit
    ;
    Sooknoi, Tawan
    Ethane dehydrogenation over [Ga]HZSM-5 catalyst were studied to probe activity of various gallium species (Ga<inf>2</inf>O<inf>3</inf>, GaO <sup>+</sup>, Ga<sup>+</sup>, and GaH<inf>2</inf><sup>+</sup>) in a pulsed reactor. H<inf>2</inf>-TPR was used for characterizing the reducible Ga species. It was found that the activity of [Ga]HZSM-5 can be regulated by the H <inf>2</inf> treatment. Among the various Ga species, the H<inf>2</inf>- incorporated species (i.e. GaH<inf>2</inf><sup>+</sup>) displays the highest dehydrogenation activity ( 55% conversion) under the H<inf>2</inf> stream. However, this so-called GaH<inf>2</inf><sup>+</sup> can readily decompose in the absence of H<inf>2</inf>, presumably to Ga<sup>+</sup> that give a lower ethane conversion ( 30%). While the Ga oxide species, which may well be retained as isolated Ga<inf>2</inf>O<inf>3</inf> and exchangeable GaO<sup>+</sup>, provide the lowest dehydrogenation activity ( 25% conversion). The lower activity is observed with an increase in the Si/Al ratio of the host zeolite, suggesting that the active site is associated with the negative framework charge, presumably as a charge balancing cation (i.e. GaH<inf>2</inf><sup>+</sup>, Ga<sup>+</sup>, GaO<sup>+</sup>). In addition, treatment with hydrogen and steam can readily disperse occluded Ga<inf>2</inf>O<inf>3</inf> into exchangeable Ga<sup>+</sup> and GaO<sup>+</sup>, respectively. © 2013 Elsevier B.V.