Upgrading of diols by gas-phase dehydrogenation and dehydration reactions on bifunctional Cu-based oxides

• Published in: Catalysis science & technology 2014-01, Vol.4 (9), p.3203-3213
• Main Authors: Torresi, P. A., Díez, V. K., Luggren, P. J., Di Cosimo, J. I.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Copper; Dehydration; Dehydrogenation; Diols; Ketones; Surface chemistry
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C4CY00639A

Biomass-derived short-chain polyols can be transformed into valuable oxygenates used as building blocks. The gas phase conversion of a model molecule of 1,3-diols (1,3-butanediol), was studied on bifunctional Cu–Mg, Cu–Al and Cu–Mg–Al mixed oxide catalysts that exhibit surface Cu 0 particles and acid–base properties. A series of Z CuMgAl catalysts ( Z = 0.3–61.2 wt.% Cu, Mg/Al = 1.5 molar ratio) was prepared by coprecipitation and thoroughly characterized by several techniques such as BET surface area, TPR-N 2 O chemisorption, XRD and TPD of CO 2 . The Z CuMgAl catalysts promote the upgrading of diols by a series of dehydrogenation and/or dehydration reactions proceeding at reaction rates that depend on the copper content ( Z ). The overall activity increases linearly with the amount of surface Cu 0 species thereby confirming the participation of metallic sites in the rate-limiting steps. Besides, surface Cu 0 sites favor the reaction pathway toward 1,3-butanediol dehydrogenation. Thus, the dehydrogenation/dehydration selectivity ratio increases with Z as a result of the enhanced amount of exposed Cu 0 particles. Z CuMgAl catalysts with Z < 8 wt.% dehydrogenate–dehydrate–hydrogenate the diol at low rates giving mainly C 4 ketones and break the intermediates forming C 1 –C 3 oxygenates; catalysts with Z > 8 wt.% have higher activity and yield valuable multifunctional C 4 oxygenates such as hydroxyketones and, to a lesser extent, unsaturated alcohols and ketones. A strongly basic Cu–Mg catalyst promotes the C–C bond cleavage reaction giving short carbon chain oxygenates at low rates; an acidic Cu–Al catalyst converts the diol into C 4 saturated ketones and olefins.