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    Item type:Publication,
    Generation of reductive Zn species over Zn/HZSM–5 catalysts for n–pentane aromatization
    (2016-09-05)
    Tamiyakul, Sikarin
    ;
    Sooknoi, Tawan
    ;
    Lobban, Lance L.
    ;
    Jongpatiwut, Siriporn
    The effects of hydrogen treatment on Zn/HZSM–5 catalysts to the evolution of zinc species and their activity in n-pentane aromatization were studied. By heating Zn/HZSM–5 catalysts under inert atmosphere, most of zinc species appeared as (ZnOH)<sup>+</sup>. The XPS and IPA–TPD results showed that using H<inf>2</inf> as a treatment gas, the hydrodehydroxylation of (ZnOH)<sup>+</sup> generated (ZnH)<sup>+</sup> species with the recovery of some Brønsted acid sites. It was found that under the hydrogen atmosphere, the H<inf>2</inf> molecule was dissociated on this Zn species and generated the H<inf>2</inf>-chemisorbed Zn species. Compared with HZSM-5 catalyst, the presence of (ZnOH)<sup>+</sup> species improved the aromatics selectivity from 11% to 22%. Nevertheless, after pre-treating Zn/HZSM–5 with H<inf>2</inf>, the formation of H<inf>2</inf>-chemisorbed Zn species remarkably increased the BTX aromatics selectivity to 31%. It was found that the H<inf>2</inf>-chemisorbed Zn species was not stable in the absence of H<inf>2</inf> however it could be regenerated upon H<inf>2</inf> treatment.