title: Oxidation and reduction of size-selected subnanometer Pd clusters on Al2O3 surface.
abstract: In this paper, we investigate uniformly dispersed size-selected Pd(n) clusters (n = 4, 10, and 17) on alumina supports. We study the changes of clustered Pd atoms under oxidizing and reducing (O2 and CO, respectively) conditions in situ using ambient pressure XPS. The behavior of Pd in the clusters is quite different from that of Pd foil under the same conditions. For all Pd clusters, we observe only one Pd peak. The binding energy of this Pd 3d peak is ~1-1.4 eV higher than that of metallic Pd species and changes slightly in CO and O2 environments. On the Pd foil however many different Pd species co-exist on the surface and change their oxidation states under different conditions. We find that the Pd atoms in direct contact with Al2O3 differ in oxidation state from the surface Pd atoms in a foil under reaction conditions. Compared to previous literature, we find that Pd 3d peak positions are greatly influenced by the different types of Al2O3 supports due to the combination of both initial and final state effects.
authors.affiliation: Jiangsu Key Laboratory for Carbon-based Functional Materials and Devices and Soochow University-Western University Joint Centre for Synchrotron Radiation Research, Institute of Functional Nano and Soft Materials, Soochow University, Suzhou, Jiangsu 215123, People's Republic of China.
authors.forename: Bao-Hua
authors.initials: BH
authors.lastname: Mao
authors.forename: Rui
authors.initials: R
authors.lastname: Chang
authors.forename: Sungsik
authors.initials: S
authors.lastname: Lee
authors.forename: Stephanus
authors.initials: S
authors.lastname: Axnanda
authors.forename: Ethan
authors.initials: E
authors.lastname: Crumlin
authors.forename: Michael E
authors.initials: ME
authors.lastname: Grass
authors.forename: Sui-Dong
authors.initials: SD
authors.lastname: Wang
authors.forename: Stefan
authors.initials: S
authors.lastname: Vajda
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liu