In Situ Single-Molecule Fluorescence Insights into Pd Nanocatalyzed Deallylation

High Resolution Image Download MS PowerPoint Slide Despite the wide application of Pd nanoparticles as heterogeneous catalysts, identifying the catalytically active species and understanding the role of nanoparticle facet structure remain challenging. Ensemble measurements can obscure active species and intrinsic heterogeneous catalytic behavior by averaging signals from multiple catalytic pathways and dynamic surface processes. Here, we employ single-molecule fluorescence microscopy (SMFM) to visualize product formation on nanoparticle surfaces to directly probe the morphology-dependent static and dynamic catalytic activity of palladium nanoparticles (Pd NPs) during a fluorogenic Tsuji–Trost deallylation reaction. Cubic Pd nanoparticles with dominant 100-type surface facets and octahedral Pd nanoparticles with dominant 111-type surface facets were used as model catalysts, and individual catalytic turnovers were monitored in real time through the formation of fluorescent OH-naphthalimide (OH-NI) from allyl-ether-naphthalimide (AE-NI). Analysis of stochastic waiting times (τ off) from single-particle trajectories reveals the distinct catalytic activity of dominant 100- and 111-type surface facets, providing quantitative data on the product formation mechanisms. Further statistical distributions and correlation analysis show dynamic heterogeneity and turnover fluctuations in catalytic activity. In addition, density functional theory (DFT) calculations on the adsorption energetics of AE-NI and other relevant species on the above facets support experimental observations of differences in catalytic activity. These results provide nanoscale-resolved evidence to support spatially localized, surface-associated catalytic events and show that nanoparticle morphology and surface facets influence both catalytic activity and heterogeneities of Pd nanocatalysts during the deallylation reaction.