The role of chromium in iron-based high-temperature water-gas shift catalysts under industrial conditions

Ariëns, M.I.; Chlan, V.; Novák, P.; van de Water, L. G.A.; Dugulan, A.I.; Brück, E.H.; Hensen, E. J.M.

doi:10.1016/j.apcatb.2021.120465

The role of chromium in iron-based high-temperature water-gas shift catalysts under industrial conditions

Title

The role of chromium in iron-based high-temperature water-gas shift catalysts under industrial conditions

Author

Ariëns, M.I. (TU Delft RST/Fundamental Aspects of Materials and Energy; Eindhoven University of Technology)
Chlan, V. (Charles University)
Novák, P. (Institute of Physics of the Academy of Sciences of the Czech Republic)
van de Water, L. G.A. (Johnson Matthey Technology Center)
Dugulan, A.I. (TU Delft RST/Fundamental Aspects of Materials and Energy; TU Delft RID/TS/Instrumenten groep)
Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Hensen, E. J.M. (Eindhoven University of Technology)

Date

2021

Abstract

Chromium promotion of iron oxide based water-gas shift (WGS) catalysts prepared via co-precipitation/calcination was investigated. Mössbauer spectroscopy and XRD evidence that chromium is incorporated in the calcined hematite (α-Fe₂O₃) precursor irrespective of the doping level (0−12 wt.%). CO-TPR shows chromium delays the reduction of hematite and the active magnetite (Fe₃O₄) phase. WGS activity was evaluated under realistic conditions for 4 days. Enhanced CO conversion was observed with increased chromium doping. Mössbauer spectra indicate that chromium incorporates into octahedral sites of magnetite and prevents reduction of Fe³⁺ to Fe²⁺ during formation of the active phase, leading to an increased Fe³⁺/Fe²⁺ ratio in octahedral sites. The higher Fe³⁺/Fe²⁺ ratio did not affect the high CO conversion associated with the structural stabilization mechanism of Cr-doping. Interpretation of the Mössbauer spectra was supported by computational modelling of various chromium and vacancy-doped magnetite structures. The bulk structure of an in situ prepared chromium-doped high-temperature WGS catalyst is best described as a partially oxidized chromium-doped magnetite phase. No surface effects of Cr-doping were found.