Copper promotion of chromium-doped iron oxide water-gas shift catalysts under industrially relevant conditions
2022
Ariëns, M.I. | van de Water, L.G.A. | Dugulan, A.I. | Brück, E. | Hensen, E.J.M.
Copper promotion of chromium-doped iron oxide prepared via co-precipitation for high-temperature water–gas shift (WGS) catalysis is investigated. Low-temperature Mössbauer spectra demonstrate that copper doping delays hematite (α-Fe₂O₃) formation in the fresh catalyst, favoring the formation of small crystallites of ferrihydrite (Fe₅HO₈∙4 H₂O). Catalysts are treated under industrial WGS conditions at 360 °C (activity evaluation) and 450 °C (ageing) at 2 and 25 bar. Mössbauer spectra show that chromium is incorporated in octahedral sites of the active magnetite (Fe₃O₄) phase, resulting in a partially oxidized structure. Copper doping did not affect the bulk magnetite structure of the activated catalyst, which points to the presence of a separate copper phase. Near-ambient pressure XPS shows that copper is in the metallic state. XPS of discharged catalysts evidenced that reaction at elevated pressure resulted in the surface reduction of Fe³⁺ to Fe²⁺. Copper promotion enhances CO conversion under high-temperature WGS conditions.
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