UNDER-COORDINATED SURFACE Al~(3+) IONS IN γ- Al2O3: THEIR ROLE IN ANCHORING AND STABILIZATION OF CATALYTICALLY ACTIVE PHASES, AND IN THE γ-to-θ PHASE TRANSITION

摘要

The importance of under-coordinated sites (defects) on metal and metal oxide surfaces has long been recognized in heterogeneous catalysis. These defects sites can serve as active centers for reactions, as well as anchoring sites for catalytic phases. In reducible oxides, for example, the interaction of metal phases with the reduced sites leads to strong metal support interaction (SMSI), that lends high thermal stability to the active metal phase. γ-Al2O3, is the most widely used industrial oxide support material due its high thermal stability, high surface area and inertness. Precious metal catalytic phases exhibit high dispersion and at the same time, remarkable stabilities on γ-Al2O3. In spite of the; extensive studies aimed at understanding the anchoring and stabilities of γ-Al2O3-supported metal catalysts, the sites where the metal atoms/clusters anchor to have not been determined unambiguously. In our previous studies we have clearly shown that metal oxide (e.g., BaO) binds to pentacoordinate Al~(3+) sites, and they remain stable to high temperatures, and also stabilize the γ-phase of alumina to high temperatures. In this presentation we are going to summarize the results of our recent studies on the multiple roles of undercoordinated Al~(3+) sites on the γ-Al2O3 surfaces in anchoring and stabilizing Pt particles, as well as in the γ-to-G phase transformation. In these studies we apply a series of spectroscopy (NMR, EXAFS, TPRX, XRD) and microscopy (STEM) techniques to gain insight into the processes taking place on the γ-Al2O3 surfaces as they interact with metal phases at high temperatures.