Sorbitol transformation in aqueous medium: Influence of metal/acid balance on reaction selectivity

The effect of the metal/acid balance of Pt/SiO2–Al2O3 catalysts on the catalytic transformation of sorbitol in aqueous medium was investigated, using four mechanical mixtures of Pt/SiO2–Al2O3 and SiO2–Al2O3 (100:0; 50:50; 25:75; 0:100). The results show that the metal/acid balance has a strong impact on catalytic performances, tuning the yields in alkanes, alcohols, ketones and heterocycles. An optimum in the metal/acid balance is obtained with the 50:50 mechanical mixture: when the metallic function is introduced in higher quantity, the C–C cleavage pathway is favoured and leads to an important CO2 yield; on the contrary, a too low proportion of platinum atoms induces a lack of metallic sites for the hydrogenation reaction. Nevertheless many hydrocarbons containing 1–4 carbon atoms are still obtained with the best balanced catalyst, evidencing some C–C cleavage activity. Hydrocarbon selectivity could be improved by new more hydrogenating metallic phases and new supports with a stronger acidity in water.