Conversion of hemicellulose-derived pentoses over noble metal supported on 1D multiwalled carbon nanotubes

Conversion of xylose was investigated over noble metals supported on multiwalled carbon nanotubes (MWCNT). Distinct metal nanoparticles were dispersed on functionalized MWCNT bearing acidic groups created by HNO3 oxidation and their catalytic performance and stability on aqueous-phase processing of pentoses were assessed. While oxidized MWCNT exhibited low activity to dehydration products, noble metal-based one-dimensional catalysts showed to be much more active. Ru decorated MWCNT was by far the most active catalyst with total xylose consumption within the first 1.5 h. Rh and Au supported samples could barely accomplish 40% conversion after 6 h. The activity order Ru > > Pd > Pt > Rh similar to Au could be established among the studied samples. Xylitol derived from direct hydrogenation of pentoses was invariably the key product formed, accomplishing selectivities within 70-85%. It revealed that the metal centers were mostly acting independently. Furfuryl alcohol was the second major product and its formation was well correlated to the concentration of acidic surface sites created upon MWCNT oxidation, evidencing a cooperative role between metal and acidic sites. The oxygenated surface groups of fresh and spent catalysts assessed by TPD were shown to be stable under the aqueous-phase processing conditions used.