OP-II-3

PP-I-41Figure 1. Turnover frequencies in the CH 4 oxidation at 700 K as a function of the mean sizeof the Pt particles supported on γ-Al 2 O 3 . The black and open squares correspond to thesamples of first and second series.In order to explain observed size effect an idea of possible thermodynamicinfluence of the particle size on the catalytic reaction rate and apparent activationenergy [2] was considered and modeling was performed. This thermodynamicapproach describes only TOF growth with decrease in particle size from 10 to 2 nmand the size dependence of the apparent activation energy of the process, but notfurther TOF reduction for the catalysts with d(Pt) < 2 nm. The most probableexplanation of this disagreement is change of reaction mechanisms or differentchemical state of active component. Indeed, the XAFS data revealed the change ofPt oxidation state at nanoparticle sizes below 2 nm. The observed decrease in theTOF value at diminishing Pt nanoparticle sizes below 2 nm seems to be due topredominantly non-metallic nature of so fine platinum particles because of a stronginteraction with the support.References[1]. N.N. Bobrov, V.N. Parmon, in: NATO Science Series II: Mathematics, Physics and Chemistry,vol. 69, Kluwer, 2002, p. 197.[2]. V.N. Parmon, Dokl. Phys. Chem. Vol. 413, 2007, p. 42.[3]. I.E. Beck, V.I. Bukhtiyarov, I.Yu. Pakharukov, V.I. Zaikovsky, V.V. Kriventsov, V.N. ParmonJournal of Catalysis Vol. 268, 2009, p. 60.AcknowledgementsWe are grateful to theFederal Education Agency for financial support withingovernmentcontract №P252/23.07.2009.294