New insight into the effect of surface oxidized groups of nanostructured carbon supported Pd catalysts on the furfural hydrogenation

The influence of the oxidized carbon moieties in the nanostructured carbon-supported Pd catalysts was studied for the furfural hydrogenation (2-propanol, 35 degrees C, 6 bar H-2). The mesoporous carbon replicas synthesized using two systems: SBA-15-furfuryl alcohol or nanostructured SiO2-sucrose and oxidized with nitric acid or hydrogen peroxide were used as the supports. The catalysts (1.5-2 wt% Pd) of similar Pd particles size (ca. 4 nm) were synthesized by the water-in-oil microemulsion procedure. Although the carbon-supported Pd, Pt catalysts have been tested for the furfural hydrogenation, the effect of oxygenated carbon groups have not been yet investigated. Present results showed that the surface O/Pd atomic ratio influenced the rate and product distribution. Over initial carbon-supported Pd, the rate was high and apart from furfuryl alcohol and tetra-hydrofurfuryl alcohol certain amount of other products was also observed. The oxidized carbon-supported catalysts were less active but more selective towards furan ring hydrogenation with almost completely inhibited other products formation reactions. The growing content of surface oxidized groups, in particular the carboxylic ones, corresponded well to the order of decreased activity. This effect has been related to a gradually reduced access of the regents to the Pd-surface sites because of the growing tendency to the hydrogen bonds formation with the participation of the oxygenated carbon groups - furfuryl alcohol - 2-propanol alcohol solvent.