A Robust Atomically Precise Nanocluster Catalyst for Simultaneous C-O and C-C Bond Cleavage in Lignin Models

The emerging metal nanoclusters are ideal molecular models for the catalysts in terms of their atomically precise structures and structure-tailored catalytic performance. However, designing an effective and robust nanocluster-based catalyst is challenging owing to its complicated synthesis approaches, poor stability, and unknown reaction mechanism. Herein, a body-centered cubic gold nanocluster, [Au₉(Dppy)₈]³⁺, is reported, which exhibits high stability in CH₂Cl₂ compared with other Au₉ clusters owing to its chemical charge and tight monomolecular protection layer. On TiO₂ nanoparticles, this Au₉ nanocluster could keep a single-cluster status to give a nanocatalyst that has strong chemisorption to H₂ and survives under harsh reaction conditions due to the strong metal-supporter interaction (SMSI). The TiO₂-supported Au₉ has served as an effective catalyst to cleave the C-C and C-O bonds of lignin model compounds, 1-(3,4-methoxyphenyl)-2-(2-methoxyphenyl)-propane-1,3-diol (LD), achieving an impressive conversion rate (92%). Moreover, the activity of nanocluster-based catalysts could vary according to the structures of nanoclusters loaded in comparison, demonstrating that the catalytic performance of nanocluster-based catalysts can be tailored by regulating nanoclusters' structures, including the core sizes, shapes, surface ligands, and metal chemical status. Finally, the durability of this nanocatalyst can be significantly improved using a ligand-free Au₉/TiO₂ catalyst, accompanied by a higher activity to C_α-C_β cleavage and slightly reduced LD conversion yield, for which the distance between reactants and metal core should be responsible according to the DFT simulations.