Abstract <p>Palladium nanoparticles were synthesized on the surface of highly oriented pyrolytic graphite by the impregnation method. Scanning tunneling microscopy and spectroscopy were used to determine the morphology of the formed individual nanoparticles and to reveal the features of their interaction with molecular oxygen and hydrogen. It was found that palladium nanoparticles, which are inert to oxygen at room temperature, begin to interact with O₂ and form a surface oxide layer as the temperature increases to 500 K. At low oxygen exposures, the formation of an oxide layer is observed on the surface area farthest from the top of the nanoparticles, while the top remains oxide-free. It was demonstrated that the process of surface reduction of oxidized palladium nanoparticles during interaction with hydrogen occurs at room temperature uniformly over the entire surface of the nanoparticles.</p>