Cyclic voltammetric studies of vanadium in V molecular sieves

Cyclic voltammetry has been used to characterize the vanadium in vanadium silicalite and vanadium aluminophosphate molecular sieves. Two sets of redox peaks corresponding to two types of vanadium species in the calcined samples, viz. V5+ ions originally present in as-synthesized samples and V5+ ions originating from V4+ species present in the as-synthesized samples, are speculated. In addition to the above, another oxidation peak is also obtained at a higher potential (+0.6 V vs. SCE) which subsequently disappears after a few cycles. Analysis of the samples by X-ray diffraction (XRD), framework IR and electron paramagnetic resonance (EPR) after coulometric reduction shows that the framework vanadium is stable.