from first principles PP-I-1

PP-III-109High Active Sulfate-Dopped Zirconium Oxide Catalysts for SkeletalIsomerization of C 4 -C 6 Alkanes. Role of Electronic Properties and SurfaceAcidity in n-Alkane ActivationUrdzhuntsev G.A., Anufrienko V.F., Yashnik S.A., Vasenin N.T., Larina Т.V.,Ovchinnikova E.B., Chumachenko V.A., Echevsky G.V.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russiaurg@ngs.ruCatalysts based on sulfated zirconia (SZ) are widely used in oil refining to isomerize C5-C6hydrocarbon fractions, showing activity in this process close to that of chlorinated alumina [1].However, for the discussed class of catalysts up till now there is no clear knowledge of thenature of their active centers and the mechanism of isomerization process on them as well [2].In the present work catalytic properties of sulfated zirconia of various composition werestudied in n-pentane isomerization and compared with their acidic properties revealed by IRspectroscopy of adsorbed CO. It is shown that the nature and strength of acid centers on asurface of the sulfated oxides not always defines their catalytic activity and the existing viewson the isomerization mechanism on SZ, and the activation stage of n-paraffin in particular,should be updated.Change of electronic state of sulfated zirconia upon either hydrogen or butane adsorption wasstudied by EPR, ESDR and magnetic susceptibility. On basis of the obtained data it is drawn aconclusion that during SZ preparation a formation of bulk defects with excess electron densitytakes place. Comparison ESDR and catalytic activity of various SZ samples allowed to find out areverse correlation between the SZ catalytic activity and the energy gap width. The mechanism ofn-paraffin activation with participation of delocalized electrons in regions with excess electrondensity is offered. The proposed mechanism does not require interaction of n-paraffin with bothlocalized electrons (Zr 3+ ) and acid centers. The role of the acid centers in the isomerizationreaction on SZ consists in stabilization of the activated state of n-paraffine.Investigation of dependences of SZ isomerization activity for individual С 4 -С 6 paraffins on theirpartial pressure has revealed that the bimolecular mechanism is realized for С 4 isomerizationreaction, while for C 5 -C 6 isomerization the monomolecular mechanism takes place.References:[1] Handbook of Petroleum Processing, Ed. D.Jones, P. Pujado, pp. 409-410 Springer, 2006[2] Yamaguchi T. Appl. Catal. A: Gen. 2001. V. 222. P. 237–246269