The field of catalytic science has emerged toward new nanoparticulate materials with novel chemical compositions. This presentation will encompass the PI's efforts on in-situ transmission electron microscopy of novel nanoparticle alloys with applications in catalysts. For these studies, we utilized aberration-corrected TEMs with capabilities to resolve the atomic positions at <1 A resolutions and chemistry at <0.4 eVs. To perform in-situ TEM, we studied the nucleation and growth of nanoparticles on liquid solutions in real time using fluidic specimen holders. Interestingly, we observed that the atomic structure of 2D materials significantly affect the crystal structure of in-situ grown Au nanoparticles. We have shown the core-shell Au-Pt nanoparticles have novel structural properties when templated on two-dimensional (2D) materials. We studied the structural and chemical transformations within these materials under elevated temperatures and gas environment. In addition, the atomic resolution studies of chemically-complex alloys provide new opportunity to correlate the structure and chemistry of catalysts with their performance.