Oxygen-Vacancy-Induced Built-In Electric Field across MoCo Dual-Atomic Site Catalyst for Promoting Hydrogen Spillover in Hydrocracking and Hydrodesulfurization

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Abstract

The design and construction of highly efficient catalytic active sites for promoting hydrogen spillover are of great significance for improving hydrocracking (HCK) and hydrodesulfurization (HDS) performance in slurry-phase hydrogenation of vacuum residue (VR) but are still challenging. Herein, we report a carbon-supported MoCo dual-atomic site catalyst (MoCo DAC/C) and propose an oxygen-vacancy-induced built-in electric field (BIEF) regulation mechanism for promoting hydrogen spillover in HCK and HDS. It was found that the coordination structure of the MoCo dual-atomic was reconstructed and formed O vacancies in situ during hydrogenation process. The formation of O vacancies not only provided macromolecular adsorption sites but also broke the electronic balance and formed a weak BIEF between the Mo and Co atoms. Meanwhile, H2 was activated at the Mo sites to form active hydrogen species. The formation of BIEF promoted the active hydrogen spillover from Mo to Co sites by a Mo–C–Co bridging bond, thus improving the hydrogenation performance greatly. In HCK of VR, the MoCo DAC/C demonstrates remarkable catalytic hydrogenation activity with TOFT calculated for total metals up to 0.77 s–1 (two times enhancement than that of Mo single atoms (SAs)/C), the per pass conversion of VR of 76 wt %, liquid product yield of 92 wt %, and coke content of only 0.55 wt %. It also shows robust HDS performance with dibenzothiophene (DBT) conversion of 70 wt %. Density functional theory reveals that the formation of the O vacancies leads to the discrepancy of Bader charge between Mo and Co atoms, and the resulting local electric field can favor the diffusion of the positively charged (+0.10 e−) H atom. This work proposes an oxygen-vacancy-induced BIEF regulation mechanism from an atomic scale for enhancing the catalytic reaction process by promoting hydrogen spillover, which provided novel insights for the design and development of high-performance hydrogenation catalysts.

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