from first principles PP-I-1

PP-III-43XPS and STM Studies of Oxidation by NO 2 of Platinum ParticlesSupported on HOPGKalinkin A.V., Sorokin A.M., Smirnov M.Yu, Bukhtiyarov V.I.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russiaavkalinkin@mail.ruA mixture of nitrogen oxides, NO x , with a prevailing contribution of nitric oxide, NO, is themain noxious component in the exhaust gas of modern internal-combustion engines operatingunder the lean conditions. The key stage of catalytic neutralization of nitrogen oxides by NO xstorage-reduction (NSR) systems is oxidation of NO to NO 2 on platinum particles. It issupposed that a possible reason of deactivation of high-dispersed NSR catalysts could beoxidation of platinum particles by nitrogen dioxide; the oxidation rate being dependent on thesize of the particles. With the view of testing this supposition, the present work is devoted tothe reaction of model catalysts with NO 2 studied by X-ray photoelectron spectroscopy (XPS)and Scanning Tunneling Microscopy (STM). The model catalysts were prepared byevaporation of platinum nanoparticles on the surface of high-oriented pyrolytic graphite(HOPG) in vacuum. Graphite was selected as the support, since it is an ideal object for STMstudies and, in contrast to oxide supports, gives an opportunity to evaluate the state of oxygenin platinum particles using XPS O 1s spectra. All experiments were performed in XPSspectrometer SPECS (Germany) using monochromatic irradiation Al K and scanningtunneling microscope GPI-300.2. It was found that there was a size effect in the roomtemperature reaction of Pt/HOPG samples with NO 2 . Indeed, based on changes observed inthe Pt 4f region, small platinum particles of D 2.5 nm in size were readily oxidized toproduce particles of Pt(II) and Pt(IV) oxides. In contrast, relatively big Pt particles of D 5.5 nm retained the metallic state in these conditions. Peculiarities of Pt particles formationon graphite and their role in graphite oxidation were also studied in this work. The reaction ofa clean HOPG surface with NO 2 was additionally studied to compare with the behaviour ofthe model catalysts. The results of this work can be used for explanation of the size effect inthe reactions of oxidation catalysis on supported metallic catalysts.This work was supported by the Russian Foundation for Basic Research (projectnos. 10-03-00596 and 12-03-91373-CT)196