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    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.
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    Xylenes production from renewable feedstocks
    (2013-12-01)
    Sooknoi, T.
    ;
    Ausavasukhi, A.
    Considerable efforts have been made during the past few years for utilizing renewable resources for chemical feedstock. As being ligno-cellulosic materials, biomass provides ready-to-use aromatic precursors for the production of xylene from biomassderived compounds. Typical approach involve fast-pyrolysis of the biomass followed by catalytic deoxygenation of the aromatic components (mainly the phenolics) in the "pyrolysis bio-oil" As the pyrolysis products always possess reactive oxygenates such as alcohols, aldehydes, and acids, the reaction requires a catalyst that readily promotes deoxygenation and/or dealkylation to form less substituted aromatic ring. Metals supported acidic oxides have been widely investigated for the reactions involving hydrogen (hydrogenation/ dehydrogenation and hydrogenolysis) and carbocation intermediates. Alternatively, refined biomass such as ethanol, fatty acid and glucose can also be converted to aromatic hydrocarbons. This approach involves dehydration, decarbonylation and/or decarboxylation to primarily produce olefinic or paraffinic hydrocarbons which can be subsequently converted to aromatic via classical acid catalysed processes. Shape selective feature of the zeolites always plays marked role for selective formation of xylenes for all approaches. This chapter will review recent attempts for xylene productions from renewable feedstock. The relation between the molecular architecture of the biomass-derived compounds and the selected catalyst system will be highlighted, together with the reaction conditions and possible on-going xylene production processes. © 2013 by Nova Science Publishers, Inc. All rights reserved.