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Peculiarities of non-conventional synthesis of V-Mo-O catalysts
|Volodymyr Sydorchuk , Svitlana Khalameida , Valeriy Zazhigalov|
Institute of Sorption and Problems of Endoecology NAS of Ukraine, 13 Gen Naumova Str., Kyiv 03164, Ukraine
V-Mo-O compositions which are base of numerical oxidative catalysts are mostly prepared by heating of mixture of vanadium and molybdenum oxides or their ammonium salts. Recently some modern particularly hydrothermal (HTT) methods have been used thereto. However approaches of non-conventional chemistry are not enough attracted for synthesis of indicated catalysts. We investigated influence of mechanochemical (MChT), microwave (MWT) and ultrasonic (UST) treatment of nonporous coarsely dispersed V2O5/ammonium dimolybdate (ADM) (V/Mo=0,7:0,3) powders in aqueous medium on their chemical and phase composition, porous structure, surface morphology. It should be noted that at the heart of listed techniques underlie similar physico-chemical processes: local and impact increase of temperature and pressure, heating of whole system, intensive mechanical influence on solid and strengthening of mass transfer as a result. For comparison HTT of the same composition was also studied since hydrothermal conditions are simulated during MChT, MWT and UST. It was established that origination of meso-macroporous from non-porous substances occurs: total pore volume has maximal value after MWT (1,0-1,2 cm3/g), minimal – after MChT (0,1-0,3 cm3/g). Increase of duration or temperature of treatment leads to destruction of ADM to non-stoichiometric Mo-oxides and partial V2O5 amorphization. At MChT (1-2 h) intercalation of H2O and NH3 molecules into V2O5 structure with its transformation in ammonium hexavanadate (4-6 h) takes place. Solid solution of substitution Mo in V2O5 with crystallite size 6-12 nm is formed on base indicated phases at next calcination under 300-500˚C. At annealing of samples undergone MWT, UST, HTT solid solution wasn’t found. However above 500˚C in all cases formation of V2MoO8 phase occurs. Thus non-conventional methods as well as HTT favor formation of V-Mo-O precursors which following calcination in essence leads to structuring of catalysts with changeable parameters.
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium D, by Volodymyr Sydorchuk
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-15 20:54 Revised: 2009-06-07 00:48