In-Situ Polarization-Dependent Total-Reflection Fluorescence XAFS Studies on the Structure Transformation of Pt Clusters on α-Al₂O₃(0001)

Structures of Pt species derived from Pt 4 (μ-CH 3 COO) 8 on an α-Al 2 O 3 (0001) single-crystal surface were studied by means of in-situ polarization-dependent total reflection fluorescence XAFS (EXAFS and XANES) techniques. The Pt 4 cluster framework was destroyed upon the deposition of Pt 4 (μ-CH 3 COO) 8 by the reaction on the α-Al 2 O 3 surface at room temperature. The isolated Pt species were converted to one-atomic 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 α-Al 2 O 3 surface. The raftlike Pt clusters were redispersed to isolated oxidized Pt species by the reaction with NO. They were also transferred to three-dimensional Pt particles by reduction with H 2 at 773 K.