CO2 activation on single crystal based ceria and magnesia/ceria model catalysts

Y. Lykhach; T. Staudt; R. Streber; M. P.A. Lorenz; A. Bayer; H.-P. Steinrück; J. Libuda

doi:10.1140/epjb/e2010-00110-x

2023 Impact factor 1.6

Condensed Matter and Complex Systems

Eur. Phys. J. B 75, 89-100 (2010)
https://doi.org/10.1140/epjb/e2010-00110-x

CO₂ activation on single crystal based ceria and magnesia/ceria model catalysts

Y. Lykhach¹, T. Staudt¹, R. Streber¹, M. P.A. Lorenz¹, A. Bayer¹, H.-P. Steinrück¹^,2 and J. Libuda¹^,2

¹ Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen, Germany
² Erlangen Catalysis Resource Center, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany

Corresponding author: libuda@chemie.uni-erlangen.de

Received: 30 October 2009
Revised: 23 February 2010
Published online: 7 April 2010

Abstract

Novel multifunctional ceria based materials may show an improved performance in catalytic processes involving CO₂ activation and reforming of hydrocarbons. Towards a more detailed understanding of the underlying surface chemistry, we have investigated CO₂ activation on single crystal based ceria and magnesia/ceria model catalysts. All model systems are prepared starting from well-ordered and fully stoichiometric CeO₂(111) films on a Cu(111) substrate. Samples with different structure, oxidation state and compositions are generated, including CeO_2-x/Cu(111) (reduced), MgO/CeO_2-x/Cu(111) (reduced), mixed MgO-CeO₂/Cu(111) (stoichiometric), and mixed MgO-CeO_2-x/Cu(111) (reduced). The morphology of the model surfaces is characterized by means of scanning tunneling microscopy (STM), whereas the electronic structure and reactivity is probed by X-ray photoelectron spectroscopy (XPS). The experimental approach allows us to compare the reactivity of samples containing different types of Ce³⁺, Ce⁴⁺, and Mg²⁺ ions towards CO₂ at a sample temperature of 300 K. Briefly, we detect the formation of two CO₂-derived species, namely carbonate (CO₃^2-) and carboxylate (CO₂^-) groups, on the surfaces of all investigated samples after exposure to CO₂ at 300 K. In parallel to formation of the carbonate species, slow partial reoxidation of reduced CeO_2-x/Cu(111) occurs at large doses of CO₂. The reoxidation of the reduced ceria is largely suppressed on MgO-containing samples. The tendency for reoxidation of Ce³⁺ to Ce⁴⁺ by CO₂ decreases with increasing degree of intermixing between MgO and CeO_2-x. Additionally, we have studied the stability of the formed carbonate species as a function of annealing temperature.