Heterogeneous catalysis, which is currently used in most industrial chemical processes, has an even stronger role to play in the energy transition, owing to its intrinsic ability to decrease the activation energy of thermodynamically feasible reactions.1 Present and future applications of catalysis for energy -including photo- and electrocatalysis- comprise petroleum refining, fuel cells, batteries, hydrogen production and storage, and biomass conversion.2 Heterogeneous catalysts often consist of transition metal nanoparticles and, more recently, single atoms supported on high-surface-area solids. This presentation will illustrate several fundamental aspects of nanocatalysis for energy-related reactions such as preferential oxidation of CO,3–5 methane reforming,6 and hydrodeoxygenation of biosourced compounds.7 It will be shown that the careful design of nanocatalysts, through the choice of suitable metals and supports, and the tuning of nanoparticle size and composition,1 allow improving catalytic performances. These investigations benefit from the use of advanced microscopy and spectroscopy techniques as well as computational methods,8–10 revealing the interplay between catalyst structure, reaction medium, and catalytic properties. (1) Piccolo, L. Surface Studies of Catalysis by Metals: Nanosize and Alloying Effects. In Nanoalloys: Synthesis, Structure and Properties; Alloyeau, D., Mottet, C., Ricolleau, C., Eds.; Engineering Materials; Springer London, 2012; pp 369–404. (2) New and Future Developments in Catalysis, S.L. Suib.; Elsevier: Amsterdam, 2013. (3) Zlotea, C.; Morfin, F.; Nguyen, T.-S.; Nguyen, N.-T.; Nelayah, J.; Ricolleau, C.; Latroche, M.; Piccolo, L. Nanoscale 2014, 6, 9955–9959. (4) Morfin, F.; Nguyen, T.-S.; Rousset, J.-L.; Piccolo, L. Appl. Catal. B 2016, 197, 2–13. (5) Zlotea, C.; Oumellal, Y.; Provost, K.; Morfin, F.; Piccolo, L. Appl. Catal. B 2018, 237, 1059–1065. (6) Nguyen, T. S.; Postole, G.; Loridant, S.; Bosselet, F.; Burel, L.; Aouine, M.; Massin, L.; Morfin, F.; Gélin, P.; Piccolo, L. J. Mater. Chem. A 2014, 2, 19822–19832. (7) Nguyen, T.-S.; Laurenti, D.; Afanasiev, P.; Konuspayeva, Z.; Piccolo, L. J. Catal. 2016, 344, 136–140. (8) Piccolo, L.; Li, Z. Y.; Demiroglu, I.; Moyon, F.; Konuspayeva, Z.; Berhault, G.; Afanasiev, P.; Lefebvre, W.; Yuan, J.; Johnston, R. L. Sci. Rep. 2016, 6, 35226. (9) Roiban, L.; Koneti, S.; Morfin, F.; Nguyen, T.-S.; Mascunan, P.; Aouine, M.; Epicier, T.; Piccolo, L. ChemCatChem 2017, 9, 4607–4613. (10) Goyhenex, C.; Piccolo, L. Phys. Chem. Chem. Phys. 2017, 19, 32451–32458.