0022-4766/14/5504-0757 © 2014 by Pleiades Publishing, Ltd. 757 Journal of Structural Chemistry. Vol. 55, No. 4, pp. 757-763, 2014. Original Russian Text © 2014 M. Yu. Smirnov, A. V. Kalinkin, D. A. Nazimov, V. I. Bukhtiyarov, E. I. Vovk, E. Ozensoy. AN XPS STUDY OF THE INTERACTION OF MODEL Ba/TiO 2 AND Ba/ZrO 2 NSR CATALYSTS WITH NO 2 M. Yu. Smirnov, 1 A. V. Kalinkin, 1 D. A. Nazimov, 1,2 V. I. Bukhtiyarov, 1,2 E. I. Vovk, 1,3 and E. Ozensoy 3 UDC 544.723.54:546.174 X-ray photoelectron spectroscopy is used to study the interaction of model NO 2 storage-reduction catalysts (NSR catalysts) Ba/TiO 2 and Ba/ZrO 2 with NO 2 . The catalysts are prepared on the surface of ultrathin Al 2 O 3 film substrates obtained by the FeCrAl alloy oxidation. It is shown that at room temperature the model catalysts react with NO 2 with the successive formation of surface barium nitrite and nitrate. The NO 2 reduction with the formation of barium nitrite at the initial step of the interaction is assumed to be accompanied by the oxidation of residual metallic barium and amorphous carbon impurity. It is found that the formation of barium nitrate proceeds more efficiently on Ba/ZrO 2 rather than on Ba/TiO 2 . DOI: 10.1134/S002247661404026X Keywords: model NSR catalysts, reaction with NO 2 , barium nitrite, barium nitrate, X-ray photoelectron spectroscopy. INTRODUCTION The purification of automobile exhaust gases from harmful impurities is an important practical problem for the solution of which complex catalytic systems are applied. In the composition of these systems the NSR (NO x storage- reduction) catalysts serve to neutralize nitrogen oxides [1]. They perform the following two functions: 1) oxidation of nitrogen oxides with their fixation in the form of nitrates; 2) reduction of nitrates to molecular nitrogen. Ba-containing compounds (BaO, Ba(OH) 2 or BaCO 3 ) supported on γ-Al 2 O 3 have traditionally been used as the main component absorbing NO x . In order to provide more efficient oxidation of NO to NO 2 and further to barium nitrate under oxidizing conditions and also the subsequent reduction of nitrate to nitrogen under reducing conditions platinum is introduced into the catalyst composition. A disadvantage of this type of NSR catalysts is their high susceptibility to poisoning by sulfur oxides (SO x ) that form in the exhaust gases as a result of oxidation of S-containing impurities in the fuel composition. It is found that the interaction of the catalyst with sulfur oxides in the oxidizing medium leads to the formation of stable barium sulfates, as a result of which the absorption capacity with respect to nitrogen oxides decreases [2, 3]. It was reported that the stability of the NSR catalyst to poisoning by sulfur compounds could be increased by the replacement of the traditional material of the γ- Al 2 O 3 substrate by other oxides, e.g. TiO 2 or ZrO 2 , in the presence of which barium sulfate easier decomposes in the reducing medium [4-6]. Using X-ray photoelectron spectroscopy (XPS), we have previously investigated the interaction of NO x and SO x 1 Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia; smirnov@catalysis.ru. 2 Novosibirsk State University, Russia. 3 Bilkent University, Bilkent, Ankara, Turkey. Translated from Zhurnal Strukturnoi Khimii, Vol. 55, No. 4, pp. 791-797, July-August, 2014. Original article submitted January 22, 2014.