The model oxidation catalyst α-V2O5: insights from contactless in situ microwave permittivity and conductivity measurements

The in situ microwave cavity perturbation technique was used to study the complex permittivity and conductivity of polycrystalline α-V2O5 in a tubular reactor under reactive high-temperature conditions with a TM110 cavity resonating at 9.2 GHz. The sample was investigated at 400 C in flowing air and air/n-butane mixtures while simultaneously measuring the total oxidation products CO and CO2 by gas chromatography. The V2O5 powder was identified as an n-type semiconductor and the dynamic microwave conductivity correlated well with the near-infrared (NIR) absorption assigned to V3d1 band gap states. Correlations between catalytic performance, real and imaginary parts of the permittivity, and NIR absorption allowed the differentiation between bulk and surface contributions to the charge transport in reactive atmospheres. The stability of the crystalline bulk phase was proven by in situ powder X-ray diffractometry for all applied testing conditions. (orig.)