Probing the H₂-Induced Restructuring of Pt Nanoclusters by H₂-TPD

Abstract

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/γ-Al₂O₃ samples with temperature-programmed desorption (TPD) and complementary adsorption/desorption techniques and observed that the H₂-TPD profile of Pt/γ-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 H₂-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.