Efficient lignin conversion over Ni/(Fe/Zn/Co/Mo/Cu)–WO3/Al2O3 for selectively yielding alkyl phenols

Abstract

The chemical demand for alkyl phenols (mainly extracted from fossil-derived resources) has been increasingly growing, which has accelerated global energy shortages. Due to the inherent aromaticity of lignin, its effective conversion into alkyl phenols is central to its adoption as a sustainable precursor to produce biochemicals. In this study, catalytic transfer hydrogenation (CTH) of alkali lignin was carried out in a mixed medium (isopropanol/formic acid) at 240 °C for 8 h over a series of bimetallic Ni based catalysts. The acidity and reducibility of the as-prepared catalysts are enhanced via WO₃ introduction (to form a WO₃–Al₂O₃ mixed support) and a bimetallic synergistic effect, respectively, leading to improved catalytic activity and selectivity towards alkyl phenols. Different kinds of phenolic compounds (e.g., those with substitutions of methoxyl, alkyl, alkenyl, carbonyl, carboxyl, or hydroxyl groups) were generated over these bimetallic Ni based catalysts with various combinations of Ni + Fe/Zn/Co/Mo/Cu, which was due to their own catalytic promotion of certain reactions (e.g., hydrogenation, deoxygenation, and/or hydrogenolysis). Reaction mechanisms of lignin depolymerization were proposed according to the distribution of phenolic compounds. This work provides a comprehensive investigation on yielding alkyl phenols from lignin CTH over a series of inexpensive bimetallic Ni based catalysts (Ni/(Fe/Zn/Co/Mo/Cu)–WO₃/Al₂O₃), and undertook a catalytic evaluation of the bimetallic synergistic effects on improving the chemical selectivity towards alky phenols, which is beneficial for lignin valorization.