SURFACE INTERACTIONS IN THE PT-GAMMA-AL2O3 SYSTEM

Using temperature-programmed reduction, Pt oxide deposited on γ-Al2O3 was found to be present in two phases: a particulate phase in which the Pt oxide is aggregated and has little interaction with the support, and a dispersed phase in which Pt oxide has a larger interaction with the support. The lower the concentration of Pt oxide in the dispersed phase, the stronger is the Pt oxide-support interaction. Using selective chemisorption of H2 and CO on Pt/γ-Al2O3 samples, the Pt oxide concentration in the dispersed phase was found to increase proportionally with Pt loading until a saturation concentration of 2.2 μmol Pt/m2 (BET) is reached. Beyond this concentration, the excess Pt oxide aggregates to form a particulate phase. At 500°C in O2 a quasi-equilibrium between Pt oxide in the dispersed phase and that in the particulate phase is reached. The behavior of Pt oxide on γ-Al2O3 during other various heat treatments was found, using transmission electron microscopy, to depend on Pt loading as well as temperature and chemical atmosphere. © 1979 Academic Press, Inc. All rights reserved.