Journal of Molecular Catalysis A-Chemical, Vol.416, 105-116, 2016
Vanadium oxides supported on amorphous aluminum phosphate: Structural and chemical characterization and catalytic performance in the 2-propanol reaction
The synthesis of vanadium oxide systems with V2O5 loadings below, above or corresponding to the theoretical monolayer (1-34 wt.% of V2O5) obtained by impregnation with vanadyl oxalate or vanadyl acetylacetonate of a mesoporous amorphous aluminum phosphate, AlPO4, calcined at different temperatures (from 350 degrees C to 650 degrees C), has been carried out. Materials were characterized by XRD, Raman, DR UV-vis, V-51, Al-27 and P-31 MAS NMR and nitrogen adsorption. Their acidity and reducibility were evaluated through pyridine TPD and hydrogen TPR, respectively, and their catalytic behavior in the 2-propanol reaction. The vanadium salt promoted the crystallization and loss of porosity of AlPO4, to a greater degree when acetylacetonate of vanadyl was the vanadium source and the vanadium loading increased. Similarly, the highest vanadia dispersion was obtained on AlPO4 calcined at 350 degrees C and impregnated with vanadyl oxalate. The vanadium systems were more active than their respective supports in the 2-propanol reaction. Furthermore, the weak -medium acid sites that predominate in AlPO4 and vanadia species are the active sites for the propene formation. The formation of propanone required redox sites,.the most active being those of the vanadia species in close contact with AlPO4, which were also more easily reducible. Both parallel reactions would proceed though concerted mechanisms. (C) 2016 Elsevier B.V. All rights reserved.
Keywords:Amorphous aluminum phosphate;Vanadia species;Acidity;Reducibility;Raman and UV-vis spectroscopy;V-51;Al-27 and P-31 MAS NMR;2-Propanol;Dehydration;Dehydrogenation