A Comparison of CO Oxidation by Hydroxyl and Atomic Oxygen from Water on Low-Coordinated Au Atoms

The catalytic oxidation of CO is studied at low-coordinated Au atoms using a single-crystal approach. Electron irradiation activates an otherwise unreactive overlayer of undissociated D₂O on Au(310). A low-coverage D₂O/O mixture is subsequently allowed to react at surface temperatures from 105 K upward, with CO supplied from the gas phase. X-ray photoelectron spectroscopy shows the absence of Au oxides and quantifies various O-containing species during the reaction. The dependency of the reaction rate on the surface temperature yields an activation energy for the Langmuir–Hinshelwood reaction of O­(ads) and CO­(ads) between 26 ± 4 and 42 ± 5 kJ/mol. The presented results provide evidence that O­(ads) and not OH­(ads) is the active reactant on small Au nanoparticles. In addition, the observations suggest that water has a negative effect on the reactivity of O­(ads)

Oxygen Adsorption and Water Formation on Co(0001)

Oxygen adsorption and removal on flat and defective Co(0001) surfaces have been investigated experimentally using scanning tunneling microscopy, temperature-programmed and isothermal reduction, synchrotron X-ray photoemission spectroscopy, and work function measurements under ultrahigh vacuum conditions and H₂/CO pressures in the 10^–5 mbar regime. Exposure of the Co(0001) to O₂(<i>g</i>) at 250 K leads to the formation of <i>p</i>(2 × 2) islands with a local coverage of 0.25 ML. Oxygen adsorption continues beyond 0.25 ML, reaching a saturation point of ∼0.39 ML O_ad, without forming cobalt oxide. Chemisorbed oxygen adlayers can be reduced on both flat and defective Co(0001) surfaces by heating in the presence of ∼2.3 × 10^–5 mbar H₂(<i>g</i>). The onset of the oxygen removal as water during temperature-programmed reduction experiments (1 K s^–1) is at around 450 K on flat Co(0001) and 550 K on defective Co(0001). By evaluation of isothermal reduction experiments using a kinetic model, the activation energy for water formation is found to be ∼129 ± 7 kJ/mol for the flat Co(0001) and ∼136 ± 7 kJ/mol for the defective Co(0001). Adsorbed oxygen cannot be reduced by CO­(g) on flat and defective Co(0001) using CO pressures up to 1 × 10^–5 mbar and temperatures up to 630 K

Hydrophilic Interaction Between Low-Coordinated Au and Water: H2O/Au(310) Studied with TPD and XPS

In this work, we study the relatively weak H2O Au interaction on the highly stepped and anisotropic (310) surface with temperature-programmed desorption and X-ray photoelectron spectroscopy. Compared to Au(111), we report an enhanced adsorption energy of H2O-Au(310) as observed from the (sub)monolayer desorption peak. This peak shows zero-order desorption kinetics, which we do not explain with a typical two-phase coexistence model but rather by desorption from the ends of one-dimensional structures. These could cover both the steps and (part of) the terraces. We do not observe crystallization of ice clusters as observed on Au(111). This leads to the conclusion that this stepped surface forms a hydrophilic template for H2O adsorption. We also notice that the precise orientation of the steps determines the H2O binding strength. Despite the surface's enhanced H2O interaction, we do observe any significant H2O dissociation. This indicates that the presence of low-coordinated Au atoms is not enough to explain the role of H2O in Au catalysis

Providing fundamental and applied insights into Fischer-Tropsch catalysis:Sasol-Eindhoven University of Technology collaboration

\u3cp\u3eAlthough Fischer-Tropsch synthesis (FTS) was discovered more than 90 years ago, it remains a fascinating topic, having relevance from both an industrial and academic perspective. FTS based on cobalt and iron catalysts was studied in depth during an extensive 15-year collaboration between Eindhoven University of Technology, The Netherlands, and Sasol, South Africa. The primary objective of the collaboration was to obtain fundamental information that could assist in understanding practical issues in FTS over iron and cobalt catalysts. For iron-based catalysts, industrial slurry reactor work was combined with SSITKA and DFT modeling, resulting in improved clarity, with respect to the kinetics and mechanisms of FTS. This knowledge is important, with respect to designing large-scale industrial processes. In the case of cobalt-based FTS research, the combination of commercially relevant supported cobalt catalysts with sophisticated characterization tools, as well as the application of flat model catalyst systems, has led to significantly improved knowledge of deactivation mechanisms. This improved knowledge has assisted in the understanding of new catalysts systems and regeneration processes. Finally, the success of the collaboration has been due to many factors. It has been beneficial to both parties to have had a long-term collaboration, in which important fundamental catalysis topics were investigated that often took a substantial period of time. The access to high-quality modeling and characterization tools and fundamental understanding, as well as industrially relevant supported catalysts operated under realistic conditions, has proved vital in our contribution toward the advancement of the science and technology of FTS.\u3c/p\u3