Efficient CO Oxidation at Low Temperature on Au(111)

Abstract

The rate of CO oxidation to CO2 depends strongly on the reaction temperature and characteristics of the oxygen overlayer on Au(111). The factors that contribute to the temperature dependence in the oxidation rate are (1) the residence time of CO on the surface, (2) the island size containing Au-O complexes, and (3) the local properties, including the degree of order of the oxygen layer. Three different types of oxygen--defined as chemisorbed oxygen, a surface oxide, and a bulk oxide--are identified and shown to have different reactivity. The relative populations of the various oxygen species depend on the preparation temperature and the oxygen coverage. The highest rate of CO oxidation was observed for an initial oxygen coverage of 0.5 monolayers that was deposited at 200 K where the density of chemisorbed oxygen is maximized. The rate decreases when two-dimensional islands of the surface oxide are populated and further decreases when three-dimensional bulk gold oxide forms. Our results are significant for designing catalytic processes that use Au for CO oxidation, because they suggest that the most efficient oxidation of CO occurs at low temperature--even below room temperature--as long as oxygen could be adsorbed on the surface.

Monitoring of the Plasmon Resonance of Gold Nanoparticles in Au/TiO2 Catalyst under Oxidative and Reducing Atmospheres

“…Formation of surface oxide has been previously reported for gold surfaces exposed to atomic oxygen or oxygen plasma. 22,62,63 For instance, Au(core)/ Au 2 O 3 (shell) structures with oxide shell thicknesses of about 0.7 nm were obtained when gold clusters were exposed to atomic oxygen. 62 In previous XAS studies performed on Au/ TiO 2 and Au/Al 2 O 3 catalysts, only Au particles smaller than about 3 nm were found reactive to air, leading to oxidation of about 10% of the Au atoms, whereas larger particles did not seemed to be oxidized.…”

Direct visualization of quasi-ordered oxygen chain structures on Au(110)-(1 × 2)

“…[15] To date, the majority of mechanistic studies have focused on O-covered Au(111), which roughens upon O atom adsorption [16] even at low coverage (0.1ML) and low temperature (~200 K). [17] The roughening of the surface associated with oxygen adsorption limits our ability to use STM because it is not possible to visualize adsorbates at the atomic scale. If a more wellordered system state of adsorbed O were accessible that had the same reactivity, the high spatial resolution offered by STM could be used to probe the details of adsorbate organization and overall reactivity.…”

“…[18] While at low coverage and low temperature a disordered surface is observed, STM demonstrates that ordered oxide islands form at high O coverage. [17] The activity for CO oxidation on O-covered Au(111) at 200K is a factor of ~3 times faster for the disordered low O coverage surface compared to the ordered surface oxide at half saturation. [17] In addition, the activity and selectivity for O-assisted methanol coupling on O-covered Au(111) depends on O coverage-higher activity and selectivity are observed for low O coverages.…”

“…[17] The activity for CO oxidation on O-covered Au(111) at 200K is a factor of ~3 times faster for the disordered low O coverage surface compared to the ordered surface oxide at half saturation. [17] In addition, the activity and selectivity for O-assisted methanol coupling on O-covered Au(111) depends on O coverage-higher activity and selectivity are observed for low O coverages. [19] Herein, we investigate the bonding of O on Au(110) in order to better exploit atomic-scale imaging using STM in conjunction with DFT studies.…”

Oxidation of nanoscale Au–In alloy particles as a possible route toward stable Au-based catalysts

“…The inability of bulk Au surfaces to activate O 2 is the main factor limiting their activity as an oxidation catalyst. However, Au can become an exceptionally active low-temperature oxidation catalyst if it can be supplied with atomic oxygen, e.g., Au nanoparticles on reducible metal oxide supports (13,14), Au nanoparticles on nonreducible oxides, where O 2 activation can be achieved by the activation of other small molecules (e.g., H 2 ) and generation of an Ocontaining intermediate (15), Au with chemisorbed oxygen (16), and surface or bulk Au oxides (17). Although the activity of carefully prepared Au CO oxidation catalysts is unmatched by other metals, Au nanoparticle catalysts face limitations due to their complex synthesis and their propensity for sintering.…”