Supported metal nanoparticles are used as catalysts to accelerate and steer chemical conversions to produce, e.g., transportation fuels, chemicals and medicines. Albeit of eminent importance, supported metal catalysts are almost exclusively synthesized in liquid-phase processes that are often considered ‘an art rather than a science’. Although recent results from our laboratory and others on the fundamentals of catalysts synthesis have led to many new insights, the lack of methodology to investigate directly the formation of supported nanoparticles in the liquid phase hampers progress.The key objective of this proposal is to image and thereby obtain a detailed understanding of both the genesis (synthesis) and the dynamics (catalysis) of supported metal nanoparticles in the liquid phase with nanometer resolution and in real time. To this end we will combine two recent developments: (1) a liquid-phase in situ cell for use in a transmission electron microscope (TEM) with (2) the element specificity of a Chemi-STEM that provides element specific images with nanometer resolution.. In this way we will image in the liquid phase the nucleation and growth of nanoparticles on a support. As support we plan to use materials with ordered porosity that allow imaging of genesis of nanoparticles in liquid confined in nanopores. The key objective of this proposal will be addressed in four projects (1) acquisition and implementation of a liquid-phase cell within a Chemi-STEM which is then used to study (2) ion adsorption of noble metal complexes onto silica and zeolites followed by liquid-phase reduction to form metallic nanoparticles, (3) crystallization of metal nitrates in nanopores of silica and carbon, (4) dynamics of palladium nanoparticles in liquid-phase catalysis.The new insights will move catalysts synthesis ‘from art to science’ and provide control over the properties of supported nanoparticles to arrive at novel catalysts for sustainable processes.