Stabilization of high oxidation state of platinum over basic support oxide examined by in situ laboratory XANES and temperature programmed desorption of oxygen

Support effect on the oxidation state of Pt nanoparticles was investigated by in situ laboratory XANES and O2-TPD. The support oxides used were MgO and Al2O3. In oxidizing condition, the surface of Pt nanoparticles supported on Al2O3 was rapidly oxidized to become the oxidation state of Pt(s)2O to Pt(s)O stoichiometry, where Pt(s) stands for the surface Pt atom, but further oxidation was not observed even at high temperature. On the other hand, Pt supported on MgO was highly oxidized in two steps at high temperature; rapid oxidation exceeding the stoichiometry of Pt(s)O, and slow further oxidation toward the stoichiometry of PtO2. The Pt particles on MgO would be redispersed and stabilized through the formation of atomically dispersed platinate anions, which would be tetravalent Pt cations coordinated by some oxygen anions, by the influence of the electrophobic cation of the support at high temperature and through the formation of Pt oxide cluster anions, (PtOx)ny−, where x would be less than two, at lower moderate temperature.