POLYOL CONVERSIONS INTO FURANIC DERIVATIVES ON BIMETALLIC CATALYSTS - CU-RU, CU-PT AND RU-CU

Bimetallic catalysts were prepared using two different techniques. Ruthenium or platinum was deposited on Raney copper by oxido-reduction. Ruthenium deposited on charcoal was modified by copper by catalytic reduction. Aqueous phase polyol conversions (glycerol, erythritol, xylitol, glucitol) in the range 493-533 K under 4 MPa of hydrogen show that unsaturated intermediates resulting from dehydrogenation are irreversibly adsorbed on the surface of copper-based catalysts modified or not by Ru or Pt. C-C and C-O bond cleavages observed on Raney copper occur through the nucleophilic action of adsorbed hydroxyl groups. For surface atomic ratios Ru or Pt to copper from 0-0.15, these reactions are deactivated due to the disappearance of surface hydroxyl groups. This phenomenon can be explained through the induced reduction of hydroxylated copper in the presence, at the catalyst surface, of H-2-Ru or H-2-Pt electrodes that fix their potential on the total catalyst. For surface atomic ratios Ru or Pt to copper greater than 0.15, cyclodehydration reactions leading to furanic derivatives occur through an electron transfer from copper to the second metal, thus creating electrophilic copper. In the case of ruthenium modified by copper, only the more active sites of Ru responsible for the multiple hydrogenolysis of C-C and C-O bonds are poisoned, part of the copper being deposited on the charcoal support. The remaining ruthenium not interacting with copper retains a high activity for simple hydrogenolysis of C-C and C-O bonds.