Efficacy and durability of cobalt sulfide nanoparticles and axial sulfur-coordinated cobalt single-atom composite sites in hydrogenative nitroaromatics decontamination.

Emerging single-atom materials and metal sulfides hold significant promise as alternatives to precious metal catalysts for nitroaromatics conversion; however, their intrinsic activity and durability remain insufficiently understood. Herein, sulfur and nitrogen co-doped carbon matrices incorporating CoS nanoparticles and single-atom Co with Co-N₄-S₁ coordination were constructed through a facile pyrolysis approach. Advanced characterization techniques, such as X-ray absorption fine structure (XAFS) and aberration-corrected electron microscopy, unveiled unique structural features underpinning exceptional catalytic efficiency and recyclability. The catalyst achieved a specific catalytic rate of 134 min^-1 g^-1 L for p-nitrophenol (PNP) hydrogenation, outperforming many noble metal-based catalysts. Experimental and theoretical analyses identified the Co-N₄-S₁ single-atom moiety as the primary active site, demonstrating remarkable structural stability. Axial sulfur coordination was found to fine-tune the electronic state of the central Co atom, mitigating the overbinding of reaction intermediates and enhancing PNP conversion efficiency. In contrast, CoS nanoparticles exhibited limited recyclability, with agglomeration, cobalt hydroxide formation, and dissolution observed during repeated use. This study presents a highly efficient catalyst for nitroaromatics conversion and provides a foundational framework for understanding the durability and mechanistic roles of cobalt-based active sites.