Synthesis and Catalytic Properties of Mesoporous Vanadium-Zirconium Binary Phosphates

摘要

V-containing mesoporous catalysts (V-MCM-41, V-MCM-48) were shown to possess a high activity and selectivity in reactions of hydrocarbon partial oxidation. Traditional methods synthesis of these catalysts are based on using expensive organic supramolecular templates (surfactant micelles) for pore size control. Moreover, special procedures to prevent collapse of the mesoporous structure as a result of vanadium incorporation have to be employed. Recently, to synthesize a mesoporous thermally stable silica with a high specific surface area a new method using citric acid not forming micelles has been suggested. It was of interest to apply this method for synthesis of mesoporous complex framework zirconium phosphates of NZP structure earlier shown to be active in the oxidative dehydrogenation of propane. In this work the results for synthesis of high surface area mesoporous binary framework vanadium-zirconium phosphates (VZP) via two routes: (ⅰ) sol-gel method including citric acid-complex phosphate composites and (ⅱ) mechanochemical activation (MA) of solid precursors followed by hydrothermal treatment (HTT) of MA products in the presence of surfactant are present. The composition of VZP corresponds to incorporation of V in various positions of NZP structure, and the mole ratio V:Zr:P is equal to 0.2:2:3 or 1:1:3. Genesis of VZP structure at different synthesis stages has been investigated by XRD, FTIRS, UV-Vis, ~(51)V and ~(31)P NMR. Surface properties were probed by IRS of adsorbed NO test molecule. The pore structure was characterized using the nitrogen adsorption-desorption isotherms. The activity and selectivity of the catalysts in ethane oxidative dehydrogenation and propane dehydrogenation have been studied.