In Situ Characterization of CuFe₂O₄ and Cu/Fe₃O₄ Water−Gas Shift Catalysts

Abstract

Mixtures of copper and iron oxides are used as industrial catalysts for the water-gas shift (WGS, CO + H 2 O f H 2 + CO 2 ). In-situ time-resolved X-ray diffraction, X-ray absorption fine structure, and atomic pair distribution function analysis were used to study the reduction of CuFe 2 O 4 with CO and the behavior of CuFe 2 O 4 and Cu/Fe 2 O 3 catalysts under WGS reaction conditions. MetalToxygenTmetal interactions enhance the stability of Cu 2+ and Fe 3+ in the CuFe 2 O 4 lattice, and the mixed-metal oxide is much more difficult to reduce than CuO or Fe 2 O 3 . Furthermore, after heating mixtures of CuFe 2 O 4 /CuO in the presence of CO or CO/H 2 O, the cations of CuO migrate into octahedral sites of the CuFe 2 O 4 lattice at temperatures (200-250 °C) in which CuO is not stable. Above 250 °C, copper leaves the oxide, the occupancy of the octahedral sites in CuFe 2 O 4 decreases, and diffraction lines for metallic Cu appear. From 350 to 450 °C, there is a massive reduction of CuFe 2 O 4 with the formation of metallic Cu and Fe 3 O 4 . At this point, the sample becomes catalytically active for the production of H 2 from the reaction of H 2 O with CO. Neutral Cu 0 (i.e., no Cu 1+ or Cu 2+ cations) is the active species in the catalysts, but interactions with the oxide support cannot be neglected. These studies illustrate the importance of in situ characterization when dealing with mixed-metal oxide WGS catalysts.

Electrochemical Reduction of CO2 at Temperatures Below 300 oC

“…Similar trends were also reported in this literature [17], [46], [110]. Reduction of Cu +1 to Cu is more difficult than Cu +2 to Cu [69], [111]. This rise in current density was due to the stability of Cu +1 with the support of CNT.…”

The promotion effects of Pd on Fe–Cu–Co based catalyst for higher alcohols synthesis

“…The reduction of Pd oxide was easy and occurred in the lower temperature, and the generated metallic Pd further activated hydrogen and promoted the reduction of other oxides. However, the weak diffraction peaks ascribed to CuFe 2 O 4 in the Pd-loaded samples after reduction could still be identified even under the promoted reduction effect of Pd due to the difficult reduction of CuFe 2 O 4 [16]. It has been reported that the undissociative activation of CO occurs on the sites of metal ions and metallic Cu while the dissociation of CO to C* and O* species mainly happens on the metallic sites of Fe and Co [10,17,18].…”

Comparing silver and copper as promoters in Fe-based Fischer–Tropsch catalysts using delafossite as a model compound

“…The partially reduced magnetite phase might be carburized more easily under Fischer-Tropsch conditions, thus enhancing the activity of promoted iron-based catalyst. The enhanced rate of carburization would be associated with an increased CO 2 -selectivity [13,23].…”