The evolution of surface and bulk structure of palladium nanoparticles supported on carbon is presented during simple chemical and physical treatment, The interpretation of in situ powder diffraction data was done on the ground of atomistic simulations and comparison with previously studied Pd samples supported on silica. Described are quantitative observations of changes in peak position, intensity and halfwidth of the 111 diffraction peak of palladium catalyst caused by modifying gaseous environment e.g. chemisorption of oxygen on palladium nanoclusters. The results show peak-shift occuring on chemisorption as well as variations in scattered intensity which are interpreted via atomistic simulations. The presented data suggest incorporation of carbon into the surface area of the metal particle occuring during exposition to argon at room temperature.