Metal clusters with sizes below 1 nm attract great scientific interest, but the main information on their properties still comes from quantum mechanics modeling and costly physical methods of limited availability. We have studied ultradispersed Pt/gamma-Al2O3 samples with temperature-programmed desorption (TPD) and complementary adsorption/desorption techniques and observed- that the H-2-TPD profile of Pt/gamma-Al2O3 is strongly dependent on the pretreatment conditions (0 < P-H2 <= 1 bar; 200 K <= T <= 470 K). The results corroborate recent theoretical and spectroscopic studies predicting alterations in the structure of Pt nanoclusters under H-2-treatment conditions but reveal that the restructuring needs to overcome continuous activation barriers and leads both to an increase in surface coverage and strengthening of the Pt-H bonds. This was interpreted as being a consequence of the strong interaction of Pt clusters with the support. The results extend insights into the behavior of supported metal particles and expand the potential of existing experimental techniques.