In situ Mössbauer spectroscopy study of the activation and reducibility of chromium- and aluminium-doped iron oxide based water-gas shift catalysts under industrially relevant conditions
M.I. Ariëns (Eindhoven University of Technology, TU Delft - Team Peyman Taheri, TU Delft - RST/Fundamental Aspects of Materials and Energy)
EH Brück (TU Delft - RST/Fundamental Aspects of Materials and Energy)
L.G.A. van de Water (Johnson Matthey Technology Center)
Emiel J M Hensen (Eindhoven University of Technology)
Iulian Dugulan (TU Delft - RID/TS/Instrumenten groep, TU Delft - RST/Fundamental Aspects of Materials and Energy)
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Abstract
The influence of chromium and aluminium doping on the over-reduction during activation of iron-oxide-based water-gas shift catalysts was investigated using Mössbauer spectroscopy for the first time. In situ Mössbauer spectra of catalysts exposed to industrially relevant gas compositions were recorded with increasingly reducing R factors R = [CO]*[H2]/[CO2]*[H2O]. Whereas α-Fe and cementite formed during exposure of a non-doped iron-oxide catalyst to process conditions with an R factor of 2.09, such phases were only observed at R = 4.60 for a chromium-doped catalyst, showing that chromium stabilizes the catalyst. Over-reduction was enhanced to R = 2.88 in a chromium-copper co-doped catalyst. α-Fe was already observed at R = 1.64 in an aluminium-doped catalyst, while cementite formation occurred at R = 2.09, showing that over-reduction was enhanced, the presence of aluminium delaying carburization. Co-doping copper in the aluminium-doped catalyst showed cementite formation at R = 2.09, the same as a non-doped catalyst.
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