Pd catalysts supported on different hydrophilic or hydrophobic carbonaceous substrate for furfural and 5-(hydroxymethyl)-furfural hydrogenation in water

We hydrogenated furfural and 5-(hydroxymethyl)furfural (HMF) in water in a reaction catalyzed by Pd nanoparticles on carbonaceous materials with different morphology and hydrophobic degree. The different Pd catalysts were prepared by dipping the carbonaceous material into a Pd-0 micro-emulsion. The catalyst support affected the catalytic hydrogenation of furfural and HMF. By using micrometric active carbon (AC) combined with cup-stacked carbon nanotubes (CSCNTs) and Pd0/2+ nanoparticles (Pd), we obtained a micro/nanostructured material designated Pd/CSCNT-AC, which performed better than the other carbonaceous materials containing similar Pd nanoparticle loading. Pd/CSCNT-AC produced tetrahydrofurfuryl alcohol from furfural with excellent selectivity (>99 %). Unlike Pd on hybrophobic spheroid graphite or hydrophilic AC, Pd/CSCNT-AC hydrogenated both the C=O and C=C double bonds of furfural and catalyzed HMF hydrogenation at the C=O double bond more selectively: between 85 % and 99 % selectivity toward 2,5-dihydroxymethylfuran. We also investigated how temperature, hydrogen pressure, and reaction time affected HMF hydrogenation in water. Finally, Pd/CSCNT-AC was recycled several times without significant catalytic activity loss.