Selective hydrogenation of citral to unsaturated alcohols over mesoporous Pt/Ti–Al2O3 catalysts. Effect of the reduction temperature and of the Ge addition

Pt/y%Ti–Al2O3 (y corresponding to the atomic percent of Ti in alumina, in the range 10–33%), and derived bimetallic Pt-Ge/10%Ti–Al2O3 nanocomposite catalysts were synthesized, characterized, and reduced either at 300 °C and 500 °C (this latter temperature being performed in order to generate strong metal–support interactions, i.e. a SMSI effect). The materials were characterized in detail with techniques including elemental analysis, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nitrogen physisorption to evaluate their structural and textural properties. Due to the templating approach used, well-defined mesopore structures with high surface areas and mesopore volumes are obtained for all materials. The SMSI effect, evaluated using a structure insensitive model reaction, i.e. the cyclohexane dehydrogenation, is observed to be more pronounced on the Pt/y%Ti–Al2O3 catalysts with y = 20 and 33% than on a Pt/TiO2 P25 (Degussa P25 titania) sample, showing the beneficial effect of Ti fine dispersion through incorporation in alumina matrix on the generated metal–support interaction. During citral hydrogenation reaction, the selectivity toward unsaturated alcohols (UA: nerol and geraniol) is related to Ti and/or Ge loadings on the nanocomposite, as well as reduction temperature. Both SMSI effect and Ge addition promote the UA selectivity leading to similar values than on Pt/TiO2 P25 sample.

To promote the activation of the CO bond of citral: Pt/Ti–Al2O3 and Pt-Ge/Ti–Al2O3 nanocomposites were synthesized and characterized. Due to the templating approach used, well-defined mesopore structures with high surface areas and mesopore volumes are obtained for all materials. During citral hydrogenation, both SMSI effect (generated by high reduction temperature) and modification of Pt by Ge addition promote the activation of the CO bond of citral.Figure optionsDownload high-quality image (102 K)Download as PowerPoint slideHighlights
► Pt/Ti–Al2O3 and Pt-Ge/Ti–Al2O3 catalysts were synthesized and characterized.
► Strong metal–support interactions were evaluated using cyclohexane dehydrogenation.
► SMSI effect is more pronounced on Pt/Ti–Al2O3 catalysts than on Pt/TiO2 P25 sample.
► SMSI effect promotes “nerol + geraniol” selectivity during citral hydrogenation.
► Ge addition promotes “nerol + geraniol” selectivity during citral hydrogenation.