title: Effect of O2, CO, and NO on surface segregation in a Rh0.5Pd0.5 bulk crystal and comparison to Rh0.5Pd0.5 nanoparticles.
abstract: We present an in situ study of the interaction of a bimetallic Rh(0.5)Pd(0.5) bulk crystal with O(2), CO, and NO using ambient pressure X-ray photoelectron spectroscopy (APXPS) and compare it to results for 15 nm nanoparticles with the same overall composition. The bulk crystal surface has less Rh present under both oxidizing and reducing conditions than the surface of nanoparticles under identical conditions. Segregation and oxidation/reduction proceeds faster and at lower temperature for nanoparticles than for the bulk crystal. The near surface of the Rh(0.5)Pd(0.5) bulk crystal after high temperature vacuum annealing is ca. 9% Rh measured by APXPS. Heating in 0.1 Torr O(2) to 350 °C increases the Rh surface composition to ca. 40%. The surface can then be reduced by heating in H(2) at 150 °C, leading to a chemically reduced surface with 30% Rh. Titration of CO by gas-phase O(2) from this Rh-rich surface proceeds at a much lower pressure than that on the Rh-deficient starting surface.
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Grass
authors.forename: Mita
authors.initials: M
authors.lastname: Park
authors.forename: Funda
authors.initials: F
authors.lastname: Aksoy
authors.forename: Yawen
authors.initials: Y
authors.lastname: Zhang
authors.forename: Martin
authors.initials: M
authors.lastname: Kunz
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liu
authors.forename: Bongjin S
authors.initials: BS
authors.lastname: Mun
mesh_terms: D000327:Adsorption; D000497:Alloys / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010316:Particle Size; D012211:Rhenium / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000497:Alloys; D009569:Nitric Oxide; D010165:Palladium; D012211:Rhenium; D002248:Carbon Monoxide; D010100:Oxygen