(584cj) Unraveling the Homo/Heterogeneous Catalysis Pathway of Palladium Nanocatalysts Via Single-Molecule Fluorescence Imaging of the Tsuji–Trost Reaction

Compared with the palladium molecular catalysts, the heterogeneous Pd nanocatalysts have recently increased attention and gained popularity as they potentially decrease catalyst cost, favor purification of final product, and are easily recycled. However, the mechanistic understanding of the catalytic mechanisms of palladium nanoparticle catalysts are still missing, which is partly attributed to the average signals of heterogeneous catalysts and catalytic information from most of current characterization techniques and loss of the sub-population information. Whether the reactions take place at Pd metal surface, defect edge sites of Pd nanoparticles, and/or redeposited nanoclusters through a heterogeneous pathway or leaching Pd species through a homogeneous pathway is still under debate.

To resolve these issues, we employ single-molecule fluorescence techniques, total internal reflection fluorescence microscopy (TIRFM), to investigate in situ catalytic behavior of individual palladium (Pd) nanoparticles for a fluorogenic Tsuji–Trost reaction. We synthesized nanoparticles with varied sizes and shapes and evaluated their catalytic performance by tracking the formation of single product molecules on individual nanoparticles. Our findings reveal that catalysis occurs via a heterogeneous rather than homogeneous pathway. Furthermore, a direct comparison between the single-turnover rate on particles with varied shapes shows distinct differences in reactivity, potentially attributed to facet-specific effects. The imaging approach could be extended to study other types of catalytic reactions, highlighting the power of single-molecule methods for uncovering mechanistic detail at the nanocatalysts.