from first principles PP-I-1

PP-III-82New Capabilities for XPS Studies of Ziegler-Natta Catalysts Using a Systemof Sample Loading in Inert AtmosphereNizovskii A.I., Mikenas T.B., Kalinkin A.V., Smirnov M.Yu., Bukhtiyarov V.I.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russiaalexniz@inbox.ruA lot of efforts are made since the discovery of Ziegler-Natta catalysts to find an explanationfor chemical and structural features of active sites that are responsible for polymerization of-olefins. Several models suggested for the structure of the active sites are based on analysisof structure of polymers produced in the process. At the same time there is still no direct prooffor one or another structure of the active sites. XPS is known to be highly effective methodfor studies of the nature of active sites of different heterogeneous catalysts. However, studiesof Ziegler-Natta catalysts using XPS are limited due to low resistance of the catalysts tooxygen and water vapour resulting in complete deactivation during the sample loading into avacuum chamber of a spectrometer. To resolve this problem, a special system is made inBoreskov Institute of Catalysis for loading samples into an X-ray photoelectron spectrometerSPECS in atmosphere of high-purity argon. The system makes possible to load a Ziegler-Natta catalyst from a sealed ampoule into an analytical chamber of the spectrometer inconditions eliminating a possibility of oxidation or hydration. In the present work, samples ofcatalysts for ethylene polymerization TiCl 4 /MgCl 2 are studied at different steps ofpreparation.It is established that the oxidation state of titanium – Ti 4+ – remains unchanged after fixationof titanium tetrachloride on the surface of the support. Titanium reduces intensively toproduce Ti 3+ and Ti 2+ states in the course of activation of the supported sample withtriethylaluminum. A spectrum obtained by us for the activated catalyst is similar to that ofmodel catalysts prepared in a vacuum chamber of an electron spectrometer without exposureto atmosphere [1]. In conclusion, based on these results, the technique developed allows us toobtain correct data studying samples of polymerization catalysts by XPS.References:[1] Seong Han Kim and Gabor A. Somorjai, Surf. Interface Anal. 31 (2001) 701.239