Recent Advances in PROX: Vibrational Characterization and Reactivity on the Pt₃Sn(111) Surface

C. Dupont, Y. Jugnet, F. Delbecq and D.Loffreda

University of Lyon, Institute of Chemistry, Ecole Normale Supérieure de Lyon, Lyon, France and Institut de Recherches sur la Catalyse et l'Environnement de Lyon, Villeurbanne, France

Fuel cells are well-known conversion systems for producing electricity from chemical energy. The hydrogen combustible usually contains traces of carbon monoxide (CO), which is known to be a catalyst poison. Among the technological solutions proposed for the CO removal, the selective oxidation in a hydrogen-rich environment (PROX: PReferential OXidation) has retained much attention during the last few years. The bimetallic catalysts exhibit an enhanced activity and selectivity towards PROX. In fact, the presence of a second metal, such as Ru or Sn(1-2), has already provided a remarkable improvement of CO tolerance.

In this talk, the PROX reaction is investigated on the Pt₃Sn(111)-(2x2) surface from both theoretical and experimental approaches. The first necessary step concerns the adsorption of the different species playing a part in the reaction. Hence the adsorption of all reactants and products is studied by Density Functional Theory (DFT) using the VASP code. Vibrational spectra are simulated allowing molecular recognition and a systematic comparison with HREELS spectra.

In a second part, we study the reactivity. We first focus on the key step: CO oxidation. In fact, we have to be sure that PtSn surfaces are more efficient for CO oxidation than pure platinum. DFT calculations have been performed (3) in comparison with PM-IRRAS and QMS spectra. This dual theoretical and experimental study shows a higher efficiency of PtSn alloy regarding CO oxidation. Finally, we will examine the theoretical aspect of the main other elementary steps involved in PROX mechanism such as oxygen and hydrogen dissociation, OH or H₂O formation.

(1) H.A. Gasteiger, N. Markovic, P.N. Ross and E.J. Cairns, J. Phys. Chem, 98 (1994) 617.

(2) M.M. Schubert, M.J. Kahlich, G. Feldmeyer, M. Huttner, S. Hackenberg, H.A. Gasteiger and R.J. Behm, Phys. Chem. Chem. Phys. 3 (2001) 1123.

(3) C. Dupont, Y. Jugnet and D. Loffreda, J. Am. Chem. Soc. 128 (2006) 9129.