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