TY - JOUR

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 -