Tracking the paths for the sucrose transformations over bifunctional Ru-POM/AC catalysts

摘要

The possible pathways of sugars transformation into 1,2-propanediol (PDO) have been studied, using new bifunctional catalysts for this catalytic multistep reaction. The catalysts are based on an acidic active phase (polyoxometalates, POMs) and a metallic function (Ru nanoparticles) supported over activated carbon (AC, SBET = 1190 m(2)/g). This support was loaded with 15 wt% of polyoxometalate, either phosphotungstic acid (TPA) or tungstosilicic acid (STA), while the amount of loaded ruthenium was close to 2 wt%. The catalytic materials were characterized by X-ray diffraction and electron microscopy techniques (SEM and TEM), while the surface active sites were evaluated using model reaction tests: cyclohexane dehydrogenation for metallic surface sites and isomerization of 3,3-dimethyl-1-butene for acid sites. For different sugars (sucrose, pentoses or hexoses) hydrogenation/hydrogenolysis using these catalysts in batch reactor was studied. The higher PDO selectivity was obtained in ethanol:water media and this study aims to establish the possible ways that sugars follow to achieve this transformation. The best catalytic material, 2%Ru-15%STA supported on AC, yields up to 50% of PDO selectivity when fructose is used as reactant, under moderate reaction conditions (413 K and 30 bar H-2).