Use of the Differential Charging Effect in XPS to Determine
the Nature of Surface Compounds Resulting from the Interaction
of a Pt/(BaCO₃ + CeO₂) Model Catalyst with SO_x

M. Yu. Smirnov^a, A. V. Kalinkin^a, A. A. Dubkov^b, E. I. Vovk^a, A. M. Sorokin^a,
A. I. Nizovskii^a, B. Carberry^b, and V. I. Bukhtiyarov^{a, c}

^a Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia

^b Ford Forschungszentrum Aachen GmbH, Aachen, D-52072 Germany

^c Novosibirsk State University, Novosibirsk, 630090 Russia

e-mail: smirnov@catalysis.ru

Received November 9, 2010

Abstract—Changes in the chemical composition of the surface of a Pt/(BaCO₃ + CeO₂) model NO_x storage–
reduction catalyst upon its interaction with SO_x (SO₂ (260 Pa) + O₂ (2600 Pa) + H₂O (525 Pa)) followed by
regeneration in a mixture of CO (2100 Pa) with H₂O (525 Pa) were studied by X-ray photoelectron spectros-
copy (XPS). Model catalyst samples were prepared as a thin film (about several hundreds of angstrom units in
thickness) on the surface of tantalum foil coated with a layer of aluminum oxide (~100 Å). It was found that
the Pt/BaCO₃ and Pt/CeO₂ catalyst constituents acquired different surface charges (differential charging) in the
course of photoelectron emission; because of this, it was possible to determine the nature of surface compounds
formed as a result of the interaction of the catalyst with a reaction atmosphere. It was found that barium car-
bonate was converted into barium sulfate as a result of reaction with SO_x on the surface of BaCO₃ at 150C. As
the treatment temperature in SO_x was increased to 300C, the formation of sulfate on the surface of CeO₂ was
observed. The sulfatization of CeO₂ was accompanied by the reduction of Ce(IV) to Ce(III). The regeneration
reaction of the catalyst treated in SO_x at 300C resulted in the consecutive decomposition of cerium(III) sulfate
at 500C and then barium sulfate at 600–700C. Upon the decomposition of BaSO₄, a portion of sulfur was
converted into a sulfide state, probably, because of the formation of BaS.

DOI: 10.1134/S0023158411040161

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