Achieving selective C−O bond cleavage of esters over monolayer NiMoS catalysts derived from oil-soluble polyoxometalates

Abstract

Sulfided NiMo catalysts can effectively hydrogenate oxygen-rich bio-oils into high quality hydrocarbon fuels. However, precisely controlling the cleavage of C−O bonds remains challenging. Here, we synthesized an oil-soluble precursor NiMo₆-DODA by encapsulating the polyoxometalates (POMs) (NH₄)₄[NiMo₆O₂₄H₆] (NiMo₆) with surfactants, followed by in-situ construction of an ultra-dispersed monolayer NiMoS catalyst. The “surfactant shell” of the precursor ensured its homogeneous dispersion in the oil phase, while gradually sacrificing and decomposing during the sulfidation to mitigate the aggregation of the MoS₂ nanosheets. Meanwhile, the well-defined “POMs core” established an atomic-level Ni-Mo proximity, ensuring the dominance of the Ni-promoted MoS₂ active phase. This design not only altered the adsorption configuration of esters on the NiMo catalyst but also introduced abundant edge sulfur vacancies to promote oxygen atom adsorption and accelerate C−O bond cleavage. The results showed that NiMo₆-DODA achieved 100% conversion of methyl palmitate and 100% alkane selectivity under low catalyst loading conditions. Notably, the selectivity for n-hexadecane reached 94.2%, significantly surpassing that obtained with a commercial oil-soluble precursor (69.8%). Furthermore, the catalyst maintained high activity across multiple reaction cycles and in the solvent-free conversion of real bio-oils. This strategy of pre-assembly combined with sacrificial sulfidation provides a simple and effective route for designing hydrodeoxygenation catalysts that enable precise control over ester C−O bond cleavage.