Selective hydrogenation of citral to unsaturated alcohols over mesoporous Pt/Ti–Al 2O 3 catalysts. Effect of the reduction temperature and of the Ge addition

Abstract

Pt/ y%Ti–Al 2O 3 ( y corresponding to the atomic percent of Ti in alumina, in the range 10–33%), and derived bimetallic Pt-Ge/10%Ti–Al 2O 3 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–Al 2O 3 catalysts with y = 20 and 33% than on a Pt/TiO 2 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/TiO 2 P25 sample.