Thermal treatment study of vanadium-loaded hydrotalcites employing in situ DXAS

A comparative study was made in which two hydrotalcites were loaded with vanadium employing different procedures: (1) aqueous phase impregnation, with vanadyl sulfate solution in pH 6.5 or 9.5; (2) solid phase mixing, with vanadyl sulfate or vanadium pentoxide physically mixed up. TPR investigation revealed that vanadium-loaded hydrotalcites obtained by aqueous phase impregnation in two distinct pH, resulted in different reduction profiles. The vanadium-loaded hydrotalcites were characterized by FTIR, XRD and TGA–DTA analysis. In situ dispersive XAS (DXAS) spectra obtained during thermal treatment in air showed that, for the physical mixture of solids, vanadium is oxidized above 350 °C. For the samples prepared by aqueous phase impregnation, the effect of alkaline pH was to produce polymeric vanadium species deposited onto the HT in comparison with the isolated vanadium species in acidic conditions. The influence of both, the hydrotalcite interlayer anion type and the vanadium loading procedure, on the reducibility of vanadium species is also discussed.