In heterogeneous catalysis, metal nanoparticles serve as the active centers for a wide range of industrially important reactions. Their bonding to the support, together with their chemical composition and morphology, determines catalytic performance. Gaining a detailed understanding of these local properties and their interactions within multicomponent systems is thus crucial for the rational development of new catalysts. However, while catalytic activity and selectivity are typically assessed using ensemble-averaged measurements, experimental techniques that enable direct observation of catalytic processes on a single nanoparticle remain limited. Only a small number of methods allow in situ or operando visualization of catalytic reaction dynamics at the nanoscale [1]. Here, we introduce a microscopy-based approach that utilizes the apex of a metallic nanotip as a well-defined model system emulating the surface of a spherical catalytic nanoparticle (r < 20 nm) [2]. By imaging, and analyzing the spatio-temporal dynamics of hydrogen oxidation on Rh, we directly probe structure-activity relations, lateral interactions within individual particles, and the emergent cooperative behavior between active sites. From these experimental findings, the mechanisms underlying lateral communication were deduced and further elucidated through microkinetic simulations employing two-dimensional oscillator grids [2-5]. By systematically varying particle size and geometry, as well as external reaction parameters such as temperature and reactant partial pressures, distinct spatio-temporal reaction patterns can be selectively established and reversibly interconverted. This degree of tunable control over reaction dynamics at the nanoscale provides new opportunities for optimizing catalytic systems by revealing reaction phenomena that have remained inaccessible with conventional approaches. References: [1] C. Vogt, B. M. Weckhuysen, Nat. Rev. Chem. 2022, 6, 89.[2] J. Zeininger et al. ACS Catal. 2021, 11, 10020–10027. [3] Y. Suchorski, J. Zeininger, S. Buhr, M. Raab, M. Stöger-Pollach, J. Bernardi, H. Grönbeck, G. Rupprechter, Science 2021, 372, 1314–1318. [4] M. Raab, J. Zeininger, Y. Suchorski, A. Genest, C. Weigl, G. Rupprechter, Nat. Commun. 2023, 14, 7186. [5] M. Raab, J. Zeininger, Y. Suchorski, K. Tokuda, G. Rupprechter, Nat. Commun. 2023, 14, 736.