Nanostructured surfaces

The effect of the increased vanadium content on the structure and activity of the oxide V-Zr-Si catalyst during the dehydrogenation of propane
A.V. Redkina, M.V. Kravchenko, N.D. Konovalova, V.V. Strelko
Institute for Sorption and Problems of Endoecology, Ukrainian National Academy of Sciences, 13 General Naumov Street, Kyiv 03164, Ukraine, 
E-mail: email.of. corresponding_antonina.redkina@gmail.com

Currently, ZrO2-based oxide systems are considered as unconventional catalysts for the widely introduced process of non-oxidative propane dehydrogenation (DHP) to propylene, capable in the long term to replace toxic or expensive traditional Cr2O3 or Pt-containing catalysts. It is known that the surface of the ZrO2 support can be significantly reduced during the heat treatment process and its can be stabilized by both the creation of a mixed oxide and the application of a layer of the active component. It is shown that the active phase of vanadium oxide exhibits high stability in the process of DHP.
In this work, it was studied the influence the supportion of 10, 20, 25 and 30% V2O5 into spherical granules 0.6ZrO2-SiO2 hydrogels obtained by the sol-gel method, on the structure and properties of the formed catalysts. After hydrothermal treatment at 250 °C and calcination at 450 °C in air it was obtained amorphous samples with the surface area of the varies in the order of ~ 300, 240, 250 and 270 m2/g, with the pores volume decreases from ~ 0.48 to 0.38 m2/g, but the spatial order of mesopores distribution was increased. 
The reaction of DHP was carried out with increasing the temperature from 250 to 650 оС in a flowing quartz tube reactor. The working mixture contained 7 vol. % of propane in argon. After the reaction, the specific surface area of the catalysts, depending on the increase in the vanadium content, respectively decreased to ~ 140, 55, 36 and 30 m2/g. The pore volume of the samples changed to 0.3-0.23 cm3/g, and the average pore diameter increased from ~ 6 nm to 9, 16, 27 and 31 nm. After the reaction, X-ray phase analysis was shown the presence of t-ZrO2 phase in the samples, the intensity of reflexes of which was increased with the content of vanadium. At a concentration of 25% V2O5, the phases m-ZrO2 and to varying degrees of reduced vanadium oxide were manifested, and at 30% V2O5 - additionally ZrV2O7. At high selectivity to propylene, catalysts with a V2O5 content of more than 10% were shown a lower yield of propane, but it was greater than that of industrial Pt-Sn/Al2O3. The obtained data may be evidence of the decisive influence of the pore nanostructure of the oxide V-Zr-Si catalyst on the during of the gas-phase propane dehydrogenation reaction.