Cooperative Effects between Ni-Mo Alloy Sites and Defective Structures over Hierarchical Ni-Mo Bimetallic Catalysts Enable the Enhanced Hydrodeoxygenation Activity

Currently, the rational design of non-noble metal catalysts for highly efficient biomass upgrading into biofuels and chemicals is quite desired. In this regard, tuning the oxophilic property of catalysts can significantly impact their activity and selectivities to target deoxygenated products in the hydrodeoxygenation (HDO) of lignin-derived phenolics. Herein, MoOx-decorated bimetallic Ni-Mo catalysts with a unique hierarchical flower-like micro/nanostructure were fabricated via a facile dopamine-assisted hydrothermal approach and adopted in the HDO of guaiacol to produce cyclohexane. By adjusting the content of Mo species, the bimetallic Ni-Mo catalyst with a Mo/Ni molar ratio of 0.1 exhibited a superior catalytic HDO performance to the Mo-free one, as well as Al2O3-supported Ni and bimetallic Ni-Mo ones prepared by the impregnation method. Combining various comprehensive structural characterization methods and catalytic HDO tests with density functional theory calculations, it was unveiled that surface defective MoOx species in the vicinity of metallic sites could greatly promote the demethoxylation of guaiacol or reaction intermediates, while Ni-Mo alloy sites could promote the dehydroxylation of cyclohexanol intermediates. Therefore, a perfect catalytic cooperative effect between Ni-Mo alloy sites and defective MoOx structures played crucial roles in accelerating the demethoxylation and dehydroxylation processes in the HDO of guaiacol. The present surface defect-bimetal engineering approach provides a promising guide for constructing highly efficient bimetallic catalysts for the upgrading of biomass-derived phenolics.