Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and CeO2-Co3O4 catalysts
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In: Journal of catalysis, Vol. 344.2016, No. December, 23.09.2016.
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T1 - Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and CeO2-Co3O4 catalysts
AU - Lukashuk, Liliana
AU - Föttinger, Karin
AU - Kolar, Elisabeth
AU - Rameshan, Christoph
AU - Teschner, Detre
AU - Hävecker, Michael
AU - Knop-Gericke, Axel
AU - Yigit, Nevzat
AU - Li, Hao
AU - McDermott, Eamon
AU - Stöger-Pollach, Michael
AU - Rupprechter, Günther
N1 - Publisher Copyright: © 2016 The Author(s)
PY - 2016/9/23
Y1 - 2016/9/23
N2 - Co3O4 is a promising catalyst for removing CO from H2 streams via the preferential CO oxidation (PROX). A Mars-van-Krevelen redox mechanism is often suggested but a detailed knowledge especially of the oxidation state of the catalytically active surface under reaction conditions is typically missing. We have thus utilized operando X-ray absorption spectroscopy to examine structure and oxidation state during PROX, and near atmospheric pressure-XPS at low photoelectron kinetic energies and thus high surface sensitivity to monitor surface composition changes. The rather easy surface reduction in pure CO (starting already at ∼100 °C) and the easy reoxidation by O2 suggest that molecularly adsorbed CO reacts with lattice oxygen, which is replenished by gas phase O2. Nevertheless, the steady state concentration of oxygen vacancies under reaction conditions is too low even for XPS detection so that both the bulk and surface of Co3O4 appear fully oxidized during PROX. Furthermore, the effect of adding CeO2 (a less active material) to Co3O4 was studied. Promotion of Co3O4 with 10 wt% CeO2 increases the reduction temperatures in CO and H2 and enhances the PROX activity. Since CeO2 is a less active material, this can only be explained by a higher activity of the Co-O-Ce interface.
AB - Co3O4 is a promising catalyst for removing CO from H2 streams via the preferential CO oxidation (PROX). A Mars-van-Krevelen redox mechanism is often suggested but a detailed knowledge especially of the oxidation state of the catalytically active surface under reaction conditions is typically missing. We have thus utilized operando X-ray absorption spectroscopy to examine structure and oxidation state during PROX, and near atmospheric pressure-XPS at low photoelectron kinetic energies and thus high surface sensitivity to monitor surface composition changes. The rather easy surface reduction in pure CO (starting already at ∼100 °C) and the easy reoxidation by O2 suggest that molecularly adsorbed CO reacts with lattice oxygen, which is replenished by gas phase O2. Nevertheless, the steady state concentration of oxygen vacancies under reaction conditions is too low even for XPS detection so that both the bulk and surface of Co3O4 appear fully oxidized during PROX. Furthermore, the effect of adding CeO2 (a less active material) to Co3O4 was studied. Promotion of Co3O4 with 10 wt% CeO2 increases the reduction temperatures in CO and H2 and enhances the PROX activity. Since CeO2 is a less active material, this can only be explained by a higher activity of the Co-O-Ce interface.
KW - Ceria promoter
KW - Cobalt oxide
KW - Hydrogen
KW - NAP-XPS
KW - Operando XAS
KW - Oxidation state
KW - PROX
UR - http://www.scopus.com/inward/record.url?scp=84988662820&partnerID=8YFLogxK
U2 - 10.1016/j.jcat.2016.09.002
DO - 10.1016/j.jcat.2016.09.002
M3 - Article
AN - SCOPUS:84988662820
VL - 344.2016
JO - Journal of catalysis
JF - Journal of catalysis
SN - 0021-9517
IS - December
ER -
