Applied Surface Science 428 (2018) 972–976 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Full Length Article Comparative XPS study of interaction of model and real Pt/C catalysts with NO 2 M.Yu. Smirnov ∗ , A.V. Kalinkin, E.I. Vovk, P.A. Simonov, E.Yu. Gerasimov, A.M. Sorokin, V.I. Bukhtiyarov Boreskov Institute of Catalysis SB RAS, 630090 Novosibirsk, Russia a r t i c l e i n f o Article history: Received 6 July 2017 Received in revised form 18 September 2017 Accepted 24 September 2017 Available online 28 September 2017 Keywords: Platinum Carbon supports XPS Nitrogen dioxide Core-shell Pt oxide/Pt metal particles a b s t r a c t XP Spectroscopy is used to compare the states of the supported platinum particles in the samples of the Pt/Sibunit catalyst and the Pt/HOPG model system after treating in NO 2 at room temperature and pressure of 3 × 10 -6 mbar. It is shown that in both cases the platinum particles are not oxidized completely. The comparison of the spectra obtained for the Pt/Sibunit sample in the Pt 4f and Pt 3d 5/2 regions with the use of Al K ˛ and Ag L  radiations serves as a basis for an assumption that the particles of platinum after being treated in NO 2 have the core (metallic Pt) − shell (platinum oxides) structure. © 2017 Elsevier B.V. All rights reserved. 1. Introduction The physicochemical studies of the model systems which chem- ical composition is identical to that of real catalysts are widely used for revealing the nature of the compounds formed on the surface of catalysts in the conditions of catalytic reaction. Quite often the model systems of the supported heterogeneous catalysts represent the particles of active component on the surface of the support, bulk or prepared as a thin film (tens of nm thick) on the substrate of metal foil [1,2]. The main advantage of the model systems when stud- ied with XPS is good spectral characteristics (high signal intensity and high resolution in binding energy) of the active component- related signal, which is due to the morphology of the system itself. At the same time the treatment of such samples in the reaction medium can be carried out directly in the vacuum chambers of XPS spectrometer at the conditions close to those of real catalysis. Nevertheless, even in the case when compositions of the real catalyst and the corresponding model system are similar, the ques- tion arises on how adequately the model system describes the behavior of the catalyst in reaction medium. In this work XPS was used to study the interaction of the real porous catalyst Pt/Sibunit and the planar model system Pt/HOPG (HOPG = Highly Oriented ∗ Corresponding author. E-mail address: smirnov@catalysis.ru (M.Yu. Smirnov). Pyrolytic Graphite) with NO 2 at identical conditions; the obtained results were compared. 2. Materials and methods A sample of the real catalyst was prepared by redox-hydrolytic precipitation of particles of platinum oxide (II) from an alkalized H 2 PtCl 6 solution on the surface of porous carbon material Sibunit (Institute of Hydrocarbons Processing SB RAS, Omsk) with NaOOCH. A detailed description of the method is given in [3]. The content of metal platinum in the catalyst was 40 wt.%. Dispersion of the plat- inum particles determined by pulse chemisorption of CO at 20 ◦ C was 0.32, which corresponds to the average particle size of 3.4 nm. A sample of the model system was prepared by vacuum evap- oration of metal platinum on the surface of HOPG fixed onto the stainless steel sample holder. The graphite surface was pre- activated with short-term etching by argon ions of low energy (1 s, 500 eV) in order to create the defects serving as setting sites for platinum particles [4]. After deposition of platinum the sample was heated in vacuum at 300 ◦ C for 1 h for stabilization of the metal par- ticles. The detailed description of the method for preparation of the Pt/HOPG model system is given in [5]. X-ray photoelectron spectra of the Pt/Sibunit catalyst were obtained in SPECS spectrometer using non-monochromatic Al K  radiation (h = 1486.6 eV) as well as monochromatic Ag L  radi- ation (h = 2983.4 eV). The sample was fixed on the holder using https://doi.org/10.1016/j.apsusc.2017.09.205 0169-4332/© 2017 Elsevier B.V. All rights reserved.