Surface-Engineered Ru/C Catalysts for Selective Alkylcyclohexanol Production via Catalytic Transfer Hydrogenation of Lignin

Abstract

Lignin depolymerization via hydrodeoxygenation typically requires high-pressure external H2, which entails safety risks and a fossil-derived carbon footprint. Here, we report a catalytic transfer hydrogenation strategy that converts native lignin into alkylcyclohexanols over surface-engineered Ru/C catalysts, using isopropanol as a hydrogen donor. The acidic Ru/C–O surface promotes concerted C–O cleavage to yield propylcyclohexanol, whereas the bifunctional Ru/C–N surface, bearing both Lewis acid and base sites, triggers a dehydrogenation–retro-aldol pathway to produce ethylcyclohexanol. Support surface chemistry thus acts as a selectivity switch. Under optimized conditions, Ru/C–N delivers an alkylcyclohexanol yield of 30.3 wt % from eucalyptus wood powder. A quantitative sustainability assessment, based on experimental product yields and with acetone treated as either a recoverable coproduct or waste, gives an E-factor of 5.5–8.5, substantially lower than that of commercial Ru/C tested under identical conditions. This work demonstrates a strategy for directing reaction selectivity through the rational design of catalyst surface chemistry, offering a sustainable route for lignin valorization without external H2 or homogeneous additives.