Introducing Metal-Sulfur Active Sites in Metal-Organic Frameworks via Post-Synthetic Modification for Hydrogenation Catalysis

Metal sulfide binary compounds, renowned for their exceptional electronic properties, are advantageous in applications such as hydrogenation, dehydrogenation, and photocatalysis. Typically, the majority of active sites in these compounds reside on the surfaces and edges of catalyst particles, leaving the bulk catalyst underutilized. This study introduces a strategy to embed metal-sulfur active sites into metal-organic frameworks (MOFs) via post-synthetic modification, exploiting the MOFs’ accessible internal surfaces. Two MOF systems, including M ₂ Cl ₂ (BBTA) (H ₂ BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole, M = Co, Ni), which features one-dimensional M–Cl chains and hexagonal channels, and M-MFU-4 l -Cl (M = Co, Ni), which contains discrete ZnM ₄ metal nodes, were selected as starting materials. The conversion processes, from M ₂ Cl ₂ (BBTA) to M ₂ (SH) ₂ (BBTA) and from M-MFU-4 l -Cl to M-MFU-4 l -SH, were executed through a two-step post-synthetic modification protocol and confirmed by single-crystal XRD, PXRD, PDF, SEM, XPS, and N ₂ sorption techniques. Catalytic performance was assessed using the reduction of 4-nitrophenol to 4-aminophenol with molecular hydrogen as a model reaction, and significant improvement in performance was observed upon introduction of the SH groups. Density functional theory calculations suggest that the flexibility of the sulfur moiety is crucial in the M–X bond cleavage pathway, enhancing hydrogen activation. This study underscores the efficacy of post-synthetic modification in developing advanced MOF-based catalysts with superior performance for selective hydrogenation reactions, highlighting the strategic advantage of incorporating polarizable sulfur components within MOFs.