abstracts - Институт катализа им. Г.К. Борескова

OP-III-16XPS AND NEXAFS IN-SITU INVESTIGATION OF VPO PRECURSORACTIVATIONBeloshapkin S., Zemlianov D., Kaichev V. 1 , Hodnett B.K., O’Mahony L.,Knop-Gericke A. 2 , Schlogl R. 2Material and Surface Science Institute, University of Limerick, Limerick, Ireland1 Boreskov Institute of Catalysis SB RAS Novosibirsk, Russia2 Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft,Faradayweg 4-6, D-14195 Berlin, GermanyE-mail: serguei.belochapkine@ul.ieThe vanadium phosphorus oxide (VPO) catalyst is commercially used for the selectiveoxidation of n-butane to maleic anhydrite (MA) [1]. The commercial VPO catalysts isprepared from vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO 4 0.5H 2 O [2]. SeveralV(IV) and V(V) phosphate phases exist in working VPO catalysts but the predominant(VO) 2 P 2 O 7 phase determines the catalytic activity because its (100) plane is the active site forthe selective activation of n-butane [3]. Ex-situ XPS analysis [4] confirms the existence ofother oxidation states (+3 and +5) before and after activation of the VPO precursor. Thepresence of V +3 atoms is explained by formation of oxygen vacancies in surface layer and itsconcentration is roughly the same for the precursor and the catalysts and do not represent anystructural changes. On the other hand the surface concentration of V +5 atom changes duringactivation of the precursor even when no VOPO 4 phase formation is detected by XRD. Insome work the presence of V +5 states is correlated with the total catalytic activity andexplained by the formation of oxidised surface zones not detectable by XRD. A more detailedpicture of the changes in electron structure of surface VPO layer can be obtained by theNEXAFS technique in the total electron yield (TEY) mode [5]. In-situ XPS and NEXAFSinvestigations of VPO precursor activation could provide us the valuable information aboutthe mechanism of surface transformation during contact with n-butane and oxygen.The aim of the presented work was the in-situ investigation of VPO precursor activationmechanism and comparison of that data with ex-situ measurement performed on the samesamples. Two VPO precursor samples were used to measurement; the VPO precursorprepared at the University of Limerick by alcoholic route [4] and industrial VPO precursorsample received from Du-Pont. The samples were activated by heating from 200 o C to 450 o C(heating rate 1 o C/min) in n-butane/oxygen mixture (1:14, 0.5 mbar total pressure). The XPSand NEXAFS spectra were recorded during the activation. The products of n-butane oxidationwere monitored by mass spectrometry. The XRD technique was used to characterise thesamples before and after activation. The morphology of the precursors was investigated by theFocused Ion Beam (FIB) technique.The result of XPS measurements shows that there are several oxidation states of vanadium onthe surface of the VPO precursors. As was mentioned before, the concentration of V +3 state346