Hydrodeoxygenation of Pyrolysis Oil in Supercritical Ethanol with Formic Acid as an In Situ Hydrogen Source over NiMoW Catalysts Supported on Different Materials

Hydrodeoxygenation (HDO) is one of the most promising approaches to upgrading pyrolysis oils, but this process normally operates over expensive noble metal catalysts (e.g., Ru/C, Pt/Al2O3) under high-pressure hydrogen gas, which raises processing costs and safety concerns. In this study, a wood-derived pyrolysis oil was upgraded in supercritical ethanol using formic acid as an in situ hydrogen source at 300 degrees C and 350 degrees C, over a series of nickel-molybdenum-tungsten (NiMoW) catalysts supported on different materials, including Al2O3, activated carbon, sawdust carbon, and multiwalled nanotubes (MWNTs). The upgrading was also conducted under hydrogen gas (an ex situ hydrogen source) for comparison. The upgrading process was evaluated by oil yield, degree of deoxygenation (DOD), and oil qualities. The NiMoW/MWNT catalyst showed the best HDO performance among all the catalysts tested at 350 degrees C, with 74.8% and 70.9% of oxygen in the raw pyrolysis oil removed under in situ and ex situ hydrogen source conditions, respectively, which is likely owing to the large pore size and volume of the MWNT support material, while the in situ hydrogen source outperformed the ex situ hydrogen source in terms of upgraded oil yields and qualities, regardless of the catalysts employed.