title: Influence of adsorbates on the electronic structure, bond strain, and thermal properties of an alumina-supported Pt catalyst.
abstract: We describe the results of an X-ray absorption spectroscopy (XAS) study of adsorbate and temperature-dependent alterations of the atomic level structure of a prototypical, noble metal hydrogenation and reforming catalyst: ∼1.0 nm Pt clusters supported on gamma alumina (Pt/γ-Al(2)O(3)). This work demonstrates that the metal-metal (M-M) bonding in these small clusters is responsive to the presence of adsorbates, exhibiting pronounced coverage-dependent strains in the clusters' M-M bonding, with concomitant modifications of their electronic structures. Hydrogen and CO adsorbates demonstrate coverage-dependent bonding that leads to relaxation of the M-M bond strains within the clusters. These influences are partially compensated, and variably mediated, by the temperature-dependent electronic perturbations that arise from cluster-support and adsorbate-support interactions. Taken together, the data reveal a strikingly fluxional system with implications for understanding the energetics of catalysis. We estimate that a 9.1 ± 1.1 kJ/mol strain exists for these clusters under H(2) and that this strain increases to 12.8 ± 1.7 kJ/mol under CO. This change in the energy of the particle is in addition to the different heats of adsorption for each gas (64 ± 3 and 126 ± 2 kJ/mol for H(2) and CO, respectively).
authors.affiliation: School of Chemical Sciences and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Small
authors.forename: Sergio I
authors.initials: SI
authors.lastname: Sanchez
authors.forename: Nebojsa S
authors.initials: NS
authors.lastname: Marinkovic
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Frenkel
authors.forename: Ralph G
authors.initials: RG
authors.lastname: Nuzzo
mesh_terms: D000042:Absorption; D000537:Aluminum Oxide / Q000737:chemistry*; D002384:Catalysis; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D010984:Platinum / Q000737:chemistry*; D013314:Stress, Mechanical; D013696:Temperature
chemical_list: D010984:Platinum; D000537:Aluminum Oxide