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In-depth characterisation of metal-support compounds in spent Co/SiO2 Fischer-Tropsch model catalysts

DOI: 10.1016/j.cattod.2019.01.065 DOI Help

Authors: Moritz Wolf (University of Cape Town) , Emma Gibson (UK Catalysis Hub; University of Glasgow) , Ezra J. Olivier (Nelson Mandela University) , Jan H. Neethling (Nelson Mandela University) , C. Richard A. Catlow (UK Catalysis Hub; University College London) , Nico Fischer (University of Cape Town) , Michael Claeys (University of Cape Town)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Catalysis Today

State: Published (Approved)
Published: January 2019

Abstract: Only little is known about the formation and morphology of metal-support compounds (MSCs) in heterogeneous catalysis. This fact can be mostly ascribed to the challenges in directly identifying these phases. In the present study, a series of Co/SiO2 model catalysts with different crystallite sizes was thoroughly characterised with focus on the identification of cobalt silicate, which is the expected metal-support compound for this particular catalyst system. The catalysts were exposed to simulated high conversion Fischer-Tropsch environment, i.e. water-rich conditions in the presence of hydrogen. The transformation of significant amounts of metallic cobalt to a hard-to-reduce phase has been observed. This particular MSC, Co2SiO4, was herein identified as needle- or platelet-type cobalt silicate structures by means of X-ray spectroscopy (XAS) and high-resolution scanning transmission electron microscopy (HRSTEM) in combination with elemental mapping. The metal-support compounds formed on top of fully SiO2-encapsulated nanoparticles, which are hypothesised to represent a prerequisite for the formation of cobalt silicate needles. Both, the encapsulation of cobalt nanoparticles by SiO2 via creeping, as well as the formation of these structures, were seemingly induced by high concentrations of water.

Journal Keywords: Cobalt catalyst; Metal-support compound; Cobalt silicate; XANES; TEM

Subject Areas: Chemistry


Instruments: B18-Core EXAFS