Effect of Copper as a Dopant on the Water Gas Shift Activity of Fe/Ce and Fe/Cr Modified Ferrites

Abstract

The role of copper as a dopant on the WGS activity of Fe/Cr and Fe/Ce catalysts has been investigated. Our catalysts were synthesized via simultaneous precipitation of substituent metal cation/s (Cu²⁺/Mⁿ⁺) with Fe³⁺ which leads to the formation of hematitic type of spinels. After activation, the catalysts are transformed into mixed or inverse spinels. Interestingly, impersonal shift activity findings reveal that copper behaves very differently when added to the Fe/Cr in comparison to the Fe/Ce catalyst formulations, namely Cu acts as a promoter for Fe/Cr, while it does not promote the activity of the Fe/Ce catalyst. Our XRD and Mössbauer studies reveal the formation of wustite phase (FeO) in activated Fe/Ce/Cu samples as the reason for their decreased activity. Moreover, TPR measurements indicate that copper promotes the Fe₃O₄ → FeO transformation to a much lower temperature which starts at 200 °C for the Fe/Ce/Cu sample compared to the Fe/Ce sample (starts at 450 °C). In contrast, no such behavior was observed for the Fe/Cr/Cu catalyst, since the reduction of Fe₃O₄ → FeO starts at 500 °C. Mössbauer studies show distortions in the cubic lattice of magnetite due to the incorporation of copper and ceria in the lattice. These distortions are reflected in the internal magnetic field of the iron octahedral sites with characteristic isomer shift ‘δ’.

Graphical Abstract