Tailoring crystal planes and oxygen vacancies of ceria for enhanced catalytic performance of single-atom Ru in hydrogenative dearomatization of lignin-derived phenols

Lignin-based guaiacol and its derivatives can be hydrogenated to synthesize 2-methoxycyclohexanols (2-MCHs), widely used in the pharmaceutical industry, while the efficient catalytic conversion of guaiacols into 2-MCHs is challenging due to the interference of the side reaction of CAr-OCH3 bond cleavage. In this work, highly selective hydrogenation of various guaiacyl lignin-derived phenols to 2-MCHs (yields of 86%-97%) was realized over a single-atom Ru-based catalyst (Ru1/o -CeO2-ov) that preferentially exposes the CeO2(111) plane and has abundant oxygen vacancies. Control experiments and mechanism studies expounded that Ru-O-Ce is the active site for hydrogenation of aromatic ring in guaiacols, and the exposed (111) plane and abundant oxygen vacancies of ceria can reduce the activation energy of aromatic ring hydrogenation, thereby enabling guaiacols to generate the corresponding hydrogenated products with high selectivity. Response surface optimization experiments indicated that temperature and time have relatively more significant effects on the 2-MCH yield. Moreover, the Ru1/o -CeO2-ov catalyst exhibited excellent reusability, and was extensively applicable to the hydrogenative dearomatization of different types of lignin-derived phenols, providing a unique solution for upgrading biomass feedstock into specific structural chemicals.