Hydrogenolysis of Asymmetric C<sub>aryl</sub>–O–C<sub>alkyl</sub> Bonds in Bio-Oils over Alloyed Catalysts: A Theoretical Insight
Rui Zuo, Jingwen Zhou, Qingliang Huang, Cong Fang, Wei An
Abstract
The mechanistic understanding of hydrogenolysis of asymmetric Caryl–O–Calkyl bonds is key to the rational design of high-performance catalysts for bio-oil upgrading. Herein, we theoretically explore hydrodeoxygenation (HDO) of anisole, a prototypical model compound for lignin-derived bio-oils, over homogeneous NiFe(111)- and PtFe(111)-alloyed surfaces within the framework of density functional theory. Our results demonstrate that hydrogenation (HY)/dehydrogenation serves as a molecular mediator for weakening/strengthening the electron delocalization of Caryl/Calkyl atom in a contradicted fashion, which consequently enables facile Caryl–O/O–Calkyl bond cleavage. Especially, the partial HY followed by deoxygenation (PHDO) via a Calkyl–OCH3 bond scission dominates in demethoxylation kinetics toward benzene formation over direct deoxygenation via a Caryl–OCH3 bond scission. Indirect demethylation of anisole via the CarylO–CH3–x bond scission (x = 1 and 2) is kinetically nearly equivalent to PHDO, leading to comparable formation of phenol and benzene on NiFe(111), but is kinetically more competitive than PHDO, leading to more phenol than benzene formation on PtFe(111). Our results highlight the importance of unbalanced measures that are essential for enhancing asymmetric Caryl–O–Calkyl bond scissions populated in bio-oil upgrading, whereby the implication for catalyst design is generated.