[Zurück]

N. Yigit, L. Lukashuk, K. Föttinger, G. Rupprechter:
"Crystal Structure Studies of Co-based Catalysts: Operando Synchrotron X-Ray Absorption and Diffraction";
Poster: 17. Österreichische Chemietage, Salzburg; 25.09.2017 - 28.09.2017; in: "17. Österreichische Chemietage", (2017).

Crystal Structure Studies of Co-based Catalysts:
Operando Synchrotron X-Ray Absorption and Diffraction
Nevzat Yigit, Liliana Lukashuk, Karin Föttinger and Günther Rupprechter
Institute of Materials Chemistry, Technische Universität Wien, Vienna, 1060, Austria
Catalytic preferential CO oxidation (PrOx), i.e. CO+H2+0.5O2→CO2+H2, is a key
reaction for removing traces of CO from the H2-rich stream. Transition metal oxides,
especially cobalt-based materials, are perspective catalysts for PrOx. However, the
current understanding of PrOx over these catalysts is mainly based on pre- and postcatalyst
characterization, and open questions include the nature of active sites and
reaction pathways. The ultimate goal of this work was to investigate the nature of the
active sites/phases of Co-based catalysts in order to understand the reaction mechanism
of PrOx. For this purpose, we compared the structural changes of Co in different
chemical compounds and oxidation states (Co3O4, and LaCoO3 perovskite) using
synchrotron-based operando X-ray absorption spectroscopy (XAS) (l811 beamline, Max-lab
II, Lund, Sweden) and operando X-ray powder diffraction (XRD) (I11beamline, Diamond, UK
and MS beamline, SLS, Switzerland).
The results of our study illustrate that during PrOx the bulk structure of LaCoO3 and
Co3O4 remain intact, when CO oxidation is dominant [1]. The fact that cobalt is
preserved in a high oxidation state in the case of LaCoO3 during PrOx explains the wide
temperature operation window for selective CO oxidation in excess of hydrogen in
comparison to Co3O4. Incorporation of Co into the LaCoO3 structure leads to partial
reduction of LaCoO3 (i.e., microstructural changes of LaCoO3 as revealed by XRD) in
the PrOx mixture and formation of defects during the preferential oxidation of CO to
CO2 in a wide temperature range of 100-300 °C. The knowledge obtained in this study
could help in developing novel catalysts for PrOx applications via tuning structural and
microstructural properties of cobalt-based materials.
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[1] Lukashuk, L. et al., Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and
CeO2-Co3O4 catalysts., J. Catal. 2016, 344, 1-15.