IN-SITU POLARIZATION-DEPENDENT TOTAL-REFLECTION FLUORESCENCE XAFS STUDIES ON THE STRUCTURE TRANSFORMATION OF PT CLUSTERS ON ALPHA-AL2O3(0001)

Structures of Pt species derived from Pt-4(mu-CH3COO)(8) on an alpha-A l2O3(0001) single-crystal surface were studied by means of in-situ pol arization-dependent total reflection fluorescence XAFS (EXAFS and XANE S) techniques. The Pt-4 cluster framework was destroyed upon the depos ition of Pt-4(mu-CH3COO)(8) by the reaction on the alpha-Al2O3 surface at room temperature. The isolated Pt species were converted to one-at omic layer thick Pt rafts with the Pt-Pt distance of 0.273 nm when the cluster was treated with H-2 at 373 K. The raftlike Pt clusters were stabilized by the formation of direct Pt-O-Al bonding with the alpha-A l2O3 surface. The raftlike Pt clusters were redispersed to isolated ox idized Pt species by the reaction with NO. They were also transferred to three-dimensional Pt particles by reduction with H-2 at 773 K.