Bi2V1−xMexO5.5−δ (Me = Ta, Ni) membranes for selective oxidation of C1–C3 alkanes in a catalytic dense membrane reactor

Pure and Me-doped γ-Bi2V1−xMexO5.5−δ (BIMEVOX) (Me = Ta, Ni) materials exhibit a transient behaviour during the oxidation of C1–C3 alkanes when shaped as dense membranes separating two compartments fed with diluted hydrocarbon and with air, respectively (catalytic dense membrane reactor). Alkenes are first produced at low conversion and CO and H2 follow at higher conversion. The H2/CO ratio increases up to values close to the stoichiometric ones and continues to increase after a peak of activity during which coke builds up. The same transient phenomena as initially observed happen after burning the coke by replacing diluted hydrocarbon by air. The fact that the membrane can be in situ regenerated means that the structure and integrity of the membranes have not been modified, as indeed shown by physicochemical analyses (XRD, SEM and XPS). The catalytic properties are mainly related to the presence of ME which affects the electronic conductivity of the materials. At variance with quite neutral BITAVOX, the behaviour of BINIVOX is close to that of BICOVOX which is also a p-type semiconductor. Only BINIVOX is able to oxidise methane quite steadily (conversion ca. 22–25 mol%) to syngas at low temperature (650 °C).