Choojun, Kittisak

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Choojun, Kittisak
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kittisak.ch@kmitl.ac.th

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    Item type:Publication,
    Effect of cobalt complex precursors on reactivity of cationic cobalt catalysts: Cyclohexane dehydrogenation
    (2019-05-10)
    Choojun, Kittisak
    ;
    Worathanaseth, Arucha
    ;
    Kuhatasanadeekul, Satu
    ;
    Kurato, Teeraporn
    ;
    Ketaniruj, Supanut
    Effect of the cobalt precursors, including [Co(bipy)<inf>3</inf>](NO<inf>3</inf>)<inf>2</inf>, [Co(NH<inf>3</inf>)<inf>5</inf>Cl]Cl<inf>2</inf>, [Co(NH<inf>3</inf>)<inf>6</inf>]Cl<inf>3,</inf> and [Co(en)<inf>2</inf>Cl<inf>2</inf>] Cl, on reactivity of the cationic Co/SiO<inf>2</inf> prepared by strong electrostatic adsorption (SEA) was investigated for the dehydrogenation of cyclohexane as a model reaction. According to the charge density of the cobalt complex, highly dispersed Co<sup>2+</sup> species and/or Co<sup>3+</sup> oxide can be obtained on the silica surface. The dehydrogenation activity is in the order of Co/SiO<inf>2</inf> catalysts prepared by [Co(bipy)<inf>3</inf>](NO<inf>3</inf>)<inf>2</inf> > [Co(NH<inf>3</inf>)<inf>5</inf>Cl]Cl<inf>2</inf> > [Co(NH<inf>3</inf>)<inf>6</inf>]Cl<inf>3</inf> > [Co(en)<inf>2</inf>Cl<inf>2</inf>] Cl, correlating to the Co<sup>2+</sup> content of the final catalysts. The cationic cobalt catalysts are more active than the pre-reduced one. Although metallic cobalt is found to be less active, the activity of cationic cobalt catalyst is enhanced under H<inf>2</inf> flow, presumably due to the formation of cobalt hydride intermediate. The inter-conversion of Co<sup>2+</sup>/cobalt hydride intermediate is readily reversible and regulated by presence of hydrogen.
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    Item type:Publication,
    Role of surface silanols and confinements of siliceous MFI supports on stability of active Ga species for ethane dehydrogenation
    (2022-05-25)
    Prakobtham, Kittipong
    ;
    Choojun, Kittisak
    ;
    Promchana, Pratya
    ;
    Sattayaporn, Suchinda
    ;
    Sooknoi, Tawan
    Effect of surface silanol and confinement of siliceous MFI supports on the anchoring stability of active Ga species was demonstrated for ethane dehydrogenation. The catalysts were prepared by impregnation of Ga(NO<inf>3</inf>)<inf>3</inf> solution on siliceous MFI (Si/Al >500) and amorphous SiO<inf>2</inf>, and characterized by XRD, XRF, SEM-EDX, H<inf>2</inf>-TPR, NH<inf>3</inf>-TPD, in situ XANES, and EXAFS. Extra-framework Ga<sup>3+</sup> species were present with different dispersions and reducibility, depending on the surface silanols. Proximity of the silanols within the surface confinement played an essential role on anchoring stability of the extra-framework Ga<sup>3+</sup> species. All Ga catalysts provided > 93% ethylene selectivity with appreciable TOF ~60 h<sup>−1</sup> for ethane dehydrogenation at 650°C. In situ XANES, EXAFS, and H<inf>2</inf>-TPR suggested that the highly dispersed extra-framework Ga<sup>3+</sup> species could exist as dimeric Ga oxide [Ga<inf>2</inf>O<inf>2</inf>]<sup>2+</sup> species. This active site could be reversibly interconverted with the less active [HGaOH]<sup>+</sup> species under the H<inf>2</inf> flow.