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Author: search.filters.author.Promchana, PratyaSubject: search.filters.subject.Ethylene

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    Selective acetylene removal from ethylene-rich feed by cross-metathesis over supported WO3 catalysts
    (2023-01-25)
    Promchana, Pratya
    ;
    Choojun, Kittisak
    ;
    Limphirat, Wanwisa
    ;
    Poo-arporn, Yingyot
    ;
    Sooknoi, Tawan
    Acetylene in ethylene-rich feed can be removed via acetylene/ethylene cross-metathesis over WO<inf>3</inf>-supported catalysts at 450 °C, yielding 1,3-butadiene with cyclohexene as a minor product. The catalyst must be treated with ethylene at 600 °C to generate a genuinely active site of tungsten (IV) alkylidene species (W=CH<inf>2</inf>). The H<inf>2</inf> treatment decreases surface W[dbnd]O concentration, and hence the activity. Raman spectroscopy shows that active single-site WO<inf>3</inf> species, including mono oxo-WO<inf>3</inf> ((O=)W(O-Si)<inf>3</inf> and (O=)W(O-Si)<inf>4</inf>) and dioxo-WO<inf>3</inf> species (O=)<inf>2</inf>W(O-Si)<inf>2</inf>) were generated in 2%WO<inf>3</inf>/SiO<inf>2</inf>, while the WO<inf>3</inf> cluster and bulk WO<inf>3</inf> exist in 3–5%WO<inf>3</inf>/SiO<inf>2</inf> and 7%WO<inf>3</inf>/SiO<inf>2</inf>, respectively. The 5%WO<inf>3</inf>/NaX and 5%WO<inf>3</inf>/NaY provide lower activity due to coke formation over the acid sites. With high surface area and confined surface silanol of 5%WO<inf>3</inf>/MCM-41% and 5%WO<inf>3</inf>/SBA-15, in situ TR-EXAFS evidences the formation of only O[dbnd]W(O-Si)<inf>3</inf>. This species provides an isolated W=CH<inf>2</inf> site with relatively higher activity and is less prone to coke formation than the WO<inf>3</inf> cluster in 5%WO<inf>3</inf>/SiO<inf>2</inf>.
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    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.