Citral hydrogenation on high surface area mesoporous TiO2–SiO2 supported Pt nanocomposites: Effect of titanium loading and reduction temperature on the catalytic performances

Abstract

Platinum-based catalysts supported on TiO2-modified mesostructured silica were prepared using the direct co-condensation of silica and titania precursors to synthesize the mixed-oxide support. The physico-chemical properties of the Pt/xTi-SBA15 samples with various xTi contents (in mol%) were further evaluated using several techniques, including elemental analysis, X-ray diffraction, N2-physisorption, H2-chemisorption, transmission electronic microscopy and the probe reaction of cyclohexane dehydrogenation to evaluate the metal–support interaction (SMSI effect). All the Pt/xTi-SBA15 samples display high specific surface areas (650–820 m2g−1) and high mesopore volumes (0.44–0.68cm3g−1), with the formation of TiO2 anatase nanoparticles since the low titanium content, i.e. 2mol%. The hexagonal organized pore structure of SBA silica is also strongly altered by the titanium adding, but mixed oxides so obtained present very particular morphology with maintaining of high surface areas.The catalytic performances of the Pt/xTi-SBA15 catalysts were estimated for the citral hydrogenation performed at 70°C under hydrogen pressure (7MPa), and discussed in terms of activity and unsaturated alcohols (UA: nerol and geraniol) selectivity. A synergetic effect on the UA selectivity was obtained on the Pt/xTi-SBA15 catalysts, compared to both Pt/SBA15 and Pt/TiO2 P25 reference samples (reduction temperature=300°C), and was explained by the specific role of the reducible TiO2 species, which under the nano-anatase form generate a strong metal–support interaction (SMSI effect) with platinum after reduction at 300°C. The formation of partially reduced support species was finally modulated by varying the reduction temperature of the catalysts. It is then possible to achieve high selectivity after reduction at 350°C, while maintaining high conversions.