Although gold-based catalysts are promising candidates for selective low-temperature CO oxidation, the reaction mechanism is not fully understood. On a Au(111) model catalyst, we observe the ...formation of gold oxide islands under exposure to atmospheric pressures of oxygen or CO oxidation reaction conditions in an in situ scanning tunneling microscope. The gold oxide formation is interpreted in line with the water-enabled dissociation of O 2 on the step edges of Au(111). Contaminants on the gold surface can strongly promote the gold oxide formation even on the terraces. On the other hand, TiO 2 nanoparticles on the Au(111) do not show any influence on the formation of the gold oxide and are thus not providing a significant amount of atomic oxygen to the gold at room temperature. Overall, the presence of gold oxide is likely under industrial conditions.
In situ scanning tunneling microscopy experiments on the initial oxidation of Pt(111) found complex intermediary platinum surface oxides, consisting of spoke wheel and stripe structures Nat. Commun. ...2017, 8, 429. While the stripes have been investigated extensively in the following, the spoke wheels are poorly understood because of their size and complexity. Here we employ atomistic thermodynamics based on an established reactive force field to investigate the structure and stability of spoke wheels at the elevated temperature (>530 K) and pressure (1–4 bar) conditions of the in situ experiments. At those conditions, the thermodynamic stability of the structural model for the spoke wheel is similar to that of the stripes, while the degree of surface oxidation is much lower. The spoke wheel is found to be much more stable than partially formed stripes with a similar degree of oxidation. These results are consistent with experimental findings, where the spoke wheel is observed first, at slightly lower oxygen pressures. They thus provide a better understanding of the oxidation pathway for Pt(111)-based catalysts in the context of oxidative catalysis.
Cobalt catalysts, although already used industrially for FischerTropsch synthesis, are prone to a number of deactivation mechanisms such as oxidation of the active phase, and the deposition of carbon ...and reaction products. We have performed near-ambient-pressure X-ray photoelectron spectroscopy on Co(0001) model catalysts during exposure to gases relevant to FischerTropsch synthesis,
i.e.
, CO and H
2
, at 0.25 mbar total pressure. At this pressure, CO seems to be more efficient at keeping the Co(0001) surface metallic than H
2
, which is the opposite behavior as reported in the literature for other pressure ranges. We offer an interpretation of these differences based on the preferred adsorption and dissociation sites of CO and H
2
compared to the oxidizing agent water (present as impurity in the gas feed and one of the products of the reaction). Additionally, detailed carbon spectra measured at the HIPPIE beamline of MAX IV allow for the distinction of different adsorbed species: CO and CO
x
species are present in correlation to the presence of oxygen on the surface. Carbidic carbon and graphitic carbon can both be removed by hydrogen, whereas adsorbed hydrocarbons possibly poison the surface.
Surface oxidation and the adsorption of different carbon species on a cobalt model catalyst were investigated using near-ambient pressure X-ray photoelectron spectroscopy in the mbar range of H
2
, CO, and FischerTropsch-like reaction conditions.
Surface oxidation and the adsorption of different carbon species on a cobalt model catalyst were investigated using near-ambient pressure X-ray photoelectron spectroscopy in the mbar range of H2, CO, ...and Fischer–Tropsch-like reaction conditions.
Cobalt catalysts, although already used industrially for Fischer-Tropsch synthesis, are prone to a number of deactivation mechanisms such as oxidation of the active phase, and the deposition of ...carbon and reaction products. We have performed near-ambient-pressure X-ray photoelectron spectroscopy on Co(0001) model catalysts during exposure to gases relevant to Fischer-Tropsch synthesis,
, CO and H
, at 0.25 mbar total pressure. At this pressure, CO seems to be more efficient at keeping the Co(0001) surface metallic than H
, which is the opposite behavior as reported in the literature for other pressure ranges. We offer an interpretation of these differences based on the preferred adsorption and dissociation sites of CO and H
compared to the oxidizing agent water (present as impurity in the gas feed and one of the products of the reaction). Additionally, detailed carbon spectra measured at the HIPPIE beamline of MAX IV allow for the distinction of different adsorbed species: CO and CO
species are present in correlation to the presence of oxygen on the surface. Carbidic carbon and graphitic carbon can both be removed by hydrogen, whereas adsorbed hydrocarbons possibly poison the surface.
Cobalt catalysts, although already used industrially for Fischer–Tropsch synthesis, are prone to a number of deactivation mechanisms such as oxidation of the active phase, and the deposition of ...carbon and reaction products. We have performed near-ambient-pressure X-ray photoelectron spectroscopy on Co(0001) model catalysts during exposure to gases relevant to Fischer–Tropsch synthesis, i.e., CO and H2, at 0.25 mbar total pressure. At this pressure, CO seems to be more efficient at keeping the Co(0001) surface metallic than H2, which is the opposite behavior as reported in the literature for other pressure ranges. We offer an interpretation of these differences based on the preferred adsorption and dissociation sites of CO and H2 compared to the oxidizing agent water (present as impurity in the gas feed and one of the products of the reaction). Additionally, detailed carbon spectra measured at the HIPPIE beamline of MAX IV allow for the distinction of different adsorbed species: CO and COx species are present in correlation to the presence of oxygen on the surface. Carbidic carbon and graphitic carbon can both be removed by hydrogen, whereas adsorbed hydrocarbons possibly poison the surface.
Transition metal dichalcogenides (TMDCs) are a type of two-dimensional (2D) material that has been widely investigated by both experimentalists and theoreticians because of their unique properties. ...In the case of cobalt sulfide, density functional theory (DFT) calculations on free-standing S–Co–S sheets suggest there are no stable 2D cobalt sulfide polymorphs, whereas experimental observations clearly show TMDC-like structures on Au(111). In this study, we resolve this disagreement by using a combination of experimental techniques and DFT calculations, considering the substrate explicitly. We find a 2D CoS(0001)-like sheet on Au(111) that delivers excellent agreement between theory and experiment. Uniquely this sheet exhibits a metallic character, contrary to most TMDCs, and exists due to the stabilizing interactions with the Au(111) substrate.
PDF