from first principles PP-I-1

OP-III-23Application of Model Systems for XPS Studies of the Mechanism ofInteraction of Supported Metal Catalysts with Gaseous Reaction MediaSmirnov M.Yu., Kalinkin A.V., Vovk E.I., Pashis A.V., Bukhtiyarov V.I.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russiasmirnov@catalysis.ruX-ray photoelectron spectroscopy (XPS) is extensively used in the field of heterogeneouscatalysis for ascertainment of the nature of active sites as well as for studies the interaction ofactive components with supports and catalysts with reaction media. However, application ofXPS method in characterization of commercial catalysts used for neutralization of noxioussubstances in the automotive exhaust is frequently problematic due to a low concentration ofthe active components that are normally platinum group metals (PGM) dispersed in a poroussupporting material. An efficient way to tackle the problem is to study model objects of thechemical composition identical to that of commercial catalysts. With the model catalystsprepared in the form of thin oxide films supporting metal particles, most of the particlesconcentrate on the outer surface of the support and, hence, are accessible for XPS analysis.This report presents a review of studies performed by the authors on supported platinumgroup metals (PGM) and gold model catalysts. The model samples were prepared in apreparation chamber of VG ESCA-3 spectrometer in the form of an oxide film (Al 2 O 3 , Fe 2 O 3 ,SiO 2 and others) of 100 Å in thickness grown in vacuum conditions on a substrate made ofa Ta foil with following evaporation of Rh, Pd, Pt or Au on the surface of the oxide film. Theaverage size of the evaporated metal particles was evaluated in TEM studies of modelsamples prepared similarly on carbon film substrates; depending on the preparationconditions, the size was varied from 2 to 10 nm. The treatment of the model catalysts ingaseous media were performed in the preparation chamber at pressures from 10 -6to 20 mbar and temperatures between 30 and 800C. With no exposure to the atmosphere, thetreated samples were transferred into an analyzer chamber for spectra registration. Thecomposition of the samples and treatment conditions were as close as possible to conditionsof the practical catalysis. The results obtained under studies of the reactions of the modelcatalysts with the following gaseous mixtures - NO x (NO+O 2 ), SO x (SO 2 +O 2 ), CO+O 2 – arediscussed in the report.This work was supported by the Russian Foundation for Basic Research (projectnos. 10-03-00596 and 12-03-91373-CT).67