Vanadyl–aluminum binary phosphate: Al/V ratio influence on their structure and catalytic behavior in the 2-propanol conversion

Abstract

The synthesis of aluminum–vanadium–phosphorus (AlVPO) systems by sol–gel method was carried out with several P/Al/V molar ratios. They were calcined at 450–550 °C as previously applied in the synthesis of amorphous AlPO 4 catalysts. Materials were characterized by chemical analysis, thermogravimetric analysis, X-ray diffraction, UV-Vis, 31 P and 27 Al MAS NMR, scanning electron microscopy and nitrogen adsorption. The textural properties and morphology of AlVPO materials were influenced by the Al/V ratio and thermal treatment. As the porosity of the solids decreased, both the BET surface areas as well as their primarily amorphous character did as well, while the vanadium content and calcination temperature increased. After calcination, the presence of two pure phosphate phases, AlPO 4 (α-cristobalite) and β-VOPO 4, was observed. Their catalytic behavior in the conversion of 2-propanol was studied. Both the activity for 2-propanol conversion and the selectivity values to propene and propanone were also greatly affected by the Al/V ratio values. Thus, the activity of the AlVPO systems increased with the aluminum content, whereas the 2-propanone selectivity decreased slightly. On the basis of kinetic study we conclude that dehydration to propene and dehydrogenation to propanone could proceed via different active sites and mechanisms.