Used as dense membranes in a catalytic dense membrane reactor, Bi 2 V 0.8 Ta 0.2 O 5.5 (BITAVOX) is more or less active in the oxidation of propane, ethane and propene according to its surface roughness. When the surface roughness is low, membranes are poorly active in the oxidation of propane (conversion <2%). CO and propene are the main products and the stability is high over long experimental periods. BITAVOX membranes with increased surface roughness exhibit high conversions in the oxidation of propane, ethane and propene. Activities and selectivities evolve with time. In a first short period (<250 s), the products are similar to those of polished samples, then mainly H 2 and CO are produced and subsequently H 2 and coke. These evolutions are probably related to surface and sub-surface restructuring due to an insufficient oxygen supply through the membrane to face the high catalytic activity induced by the increase in surface area. The results suggest that the O 2À diffusion is limited by the low electronic conductivity of BIMEVOX materials. Nevertheless the membrane is not reduced irreversibly, even in coking conditions. This is confirmed by ex situ characterisations carried out on the materials (XRD, SEM, XPS). An improvement of the electronic conductivity of this material is necessary in order to stabilize the intermediate catalytic behaviour which is interesting for syngas or H 2 production from light hydrocarbons. #

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Pure and Me-doped γ-Bi 2 V 1-x Me x O 5.5-δ (BIMEVOX) (Me = Ta, Ni) materials exhibit a transient behaviour during the oxidation of C 1-C 3 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 H 2 follow at higher conversion. The H 2 /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. This in situ regeneration of the membrane means that the structure and integrity of the membranes have not been modified, as indeed shown by physicochemical analyses (XRD, SEM, 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 (conversion ca. 22-25 mol%) to syngas at low temperature (650°C) in a quite steady manner.