Vanadium oxides supported on amorphous aluminum phosphate: Structural and chemical characterization and catalytic performance in the 2-propanol reaction

• The impregnation of a synthetic AlPO4 with vanadyl solutions promotes its crystallization and loss of porosity.
• The calcination temperature of AlPO4 and the vanadyl source clearly affect vanadia dispersion.
• The highest vanadia dispersion was obtained on AlPO4 calcined at 350 °C and impregnated with vanadyl oxalate.
• Weak-medium acid sites predominating on catalysts were responsible for propene formation, whereas redox sites determined the propanone formation.

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 °C to 650 °C), has been carried out. Materials were characterized by XRD, Raman, DR UV–vis, 51V, 27Al and 31P 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 °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.

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