from first principles PP-I-1

PP-III-12Spectral and Catalytic Study of Silica Modified Cr 2 O 3 /Al 2 O 3Dehydrogenation CatalystBekmuhamedov G.E. 1 , Egorova S.R. 1 , Kataev A.N. 1 , Zalyaliev R.F. 1 , Lamberov A.A. 11 Kazan (Volga) Federal University, Kazan, RussiaGiyjaz413@rambler.ruChromia-alumina microspherical catalysts have a great practical importance and are widelyused in the C 3 -C 5 -alkane dehydrogenation process. The effect of the silica modification on thestate of the active phase and catalytic performance of chromia-alumina catalyst was studied.The catalysts were prepared by incipient wetness impregnation of monophase boehmitesupport by aqueous solutions of the chromium and potassium compounds, and subsequentthermal activation. Catalytic properties were studied in the dehydrogenation of isobutane in afluidized bed at 570ºC.Catalyst activity and selectivity in the isobutane dehydrogenation process increased by1.5 and 2 % respectively after modification by 2.5-4.5 wt.% of silica. At the same time anincrease of the bands corresponding to the Cr(III) oct -ion in the catalytically activeCr 2 O 3 -clusters on the EPR-, UV-Vis- and Raman-spectra were observed.It was determined by UV-Vis-spectroscopy that upon modification by SiO 2 on the supportsurface Cr 2 O 3 -clusters with a lower energy of 4 A 2g → 4 T 2g and 4 A 2g → 4 T 1g electronictransitions in the Cr(III) oct -ion formed. According to the heterolytic mechanism of alkanedehydrogenation process, it causes greater interaction between the Cr(III) oct -ion and theadsorbed hydrocarbon molecule, the easier hydride-ion elimination and the C=C-bondformation.The reason of catalyst selectivity increasing upon SiO 2 modification in addition to theformation of catalytically active Cr 2 O 3 -clusters is a decrease of surface acidity, which wasinvestigated by TPD of ammonia.163