Hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol over carbon dots supported Pd catalyst

Abstract

Vanillin hydrodeoxygenation (HDO) was studied in water and methanol using palladium-decorated carbon dots (Pd/CDs). The catalyst was synthesized from photo-reduction of palladium acetate using CDs as the reducing and dispersion agent, while CDs were produced via microwave treatment of glucose and urea. Pd/CDs were characterized with XRD, TEM, FT-IR, XPS, BET and ICP-OES. The selectivity to 2‑methoxy-4-methylphenol (MMP), at vanillin conversion of 100 % after 4.0 h was 98.8 % at 140 °C under 4.0 MPa of H2 in water with 4.58 wt.% of Pd/CDs. The stability of Pd/CDs was also investigated after four times recycle under the optimal reaction conditions. CDs supported Pd reduced with NaBH4 and hydrazine hydrate (Pd/CDs-S and Pd/CDs-H) and other carbonaceous materials (active carbon and OH functionalized multi-walled carbon nanotube) supported Pd (Pd/AC and Pd/CNTs) were also investigated for comparison. The highest selectivity to MMP achieved by Pd/CDs produced via photoreduction brings a novel use of this type of catalyst in the conversion of biomass into value-added chemicals and materials.