Flexible NiCo-based catalyst for direct hydrodeoxygenation of guaiacol to cyclohexanol

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenols is an important step for bio-oil upgrading. Herein, a novel HDO system was established in the presence of nitrogen, instead of traditional hydrogen. A series of CNT-supported Ni-based catalysts was prepared and introduced in the HDO of guaiacol and other lignin-derived phenolic compounds. The bimetallic NiCo/CNT catalysts exhibited better catalytic performance during the HDO reaction, in comparison with monometallic Ni/CNT and Co/CNT catalysts. Among these catalysts, the (15 + 5)% NiCo/CNT catalyst afforded the highest guaiacol conversion (up to 100%) with cyclohexanol as the main product in isopropanol. The effects of process parameters on guaiacol conversion and product distribution were studied in detail, finding that the presence of nitrogen could help to suppress the generation of byproducts, while the presence of hydrogen would facilitate the occurrence of side reactions. The HDO reaction of guaiacol occurred possibly in two consecutive steps: the demethoxylation of guaiacol to phenol and the further hydrogenation of the aromatic ring to cyclohexanol.