title: Evaluation of Reoxidation Thresholds for γ-Al2O3-Supported Cobalt Catalysts under Fischer-Tropsch Synthesis Conditions.
abstract: Size-dependent phenomena at the nanoscale influence many applications, notably in the science of heterogeneous catalysis. In cobalt-based Fischer-Tropsch synthesis (FTS), the size of Co nanoparticles (NPs) dictates to a high degree catalyst's performance in terms of activity, selectivity, and stability. Here, a highly dispersed Re/Co/γ-Al2O3catalyst with high Co surface area per gram of catalyst was exposed to industrially relevant FTS conditions and monitored in situ by synchrotron X-ray radiation. X-ray absorption near-edge structure spectra were obtained on the cobalt K edge and Re L3edge of the working catalyst. The experimental results demonstrate development of tetrahedrally coordinated Co2+forming at the expense of metallic Co(0). The structure of the oxide resembles CoAl2O4and appears at the onset (first 5-10 h) of the reaction. Reoxidation of Co(0)is more pronounced close to the outlet of the reactor, where higher pH2O is anticipated. The state of the Re promoter does not change during the FT process. We propose that reoxidation of small Co NPs is followed by spreading of Co oxide that leads to the formation of CoxAlyOzphases. Hence, in order to avoid an irreversible loss of the active phase during process start-up, catalyst design should be restricted to Co NPs larger than 5.3 nm.
authors.affiliation: Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU) , NO-7491 Trondheim, Norway.
authors.forename: Nikolaos E
authors.identifier: 0000-0002-3915-5937
authors.initials: NE
authors.lastname: Tsakoumis
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU) , NO-7491 Trondheim, Norway.|SINTEF Materials and Chemistry , NO-7465, Trondheim, Norway.
authors.forename: John C
authors.initials: JC
authors.lastname: Walmsley
authors.affiliation: Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU) , NO-7491 Trondheim, Norway.
authors.forename: Magnus
authors.initials: M
authors.lastname: Rønning
authors.affiliation: Swiss-Norwegian Beamlines at ESRF , Grenoble F38043, France.
authors.forename: Wouter
authors.initials: W
authors.lastname: van Beek
authors.affiliation: Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU) , NO-7491 Trondheim, Norway.
authors.forename: Erling
authors.initials: E
authors.lastname: Rytter
authors.affiliation: Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU) , NO-7491 Trondheim, Norway.
authors.forename: Anders
authors.initials: A
authors.lastname: Holmen