Variation of the vanadium oxidation state within a VPO catalyst layer in a membrane reactor: XPS mapping and modelling

摘要

Recently, the feasibility of butane oxidation in an electrochemical membrane reactor (EMR) using a vanadium phosphorus oxide (VPO) catalyst layer on a tubular anodic electrode has been reported. This novel application of EMR gives rise to questions about the vanadium oxidation state (V_(OX)) under working conditions and about its spatial distribution in the catalyst layer. It has now been determined by means of position-resolved XPS measurements. In addition, model calculations on the spatial V_(OX) distribution have been performed for the first time. The simulations reveal a non-uniform 3D distribution of V_(OX) due to the relative rate of reduction and re-oxidation processes in the catalyst layer, in good agreement with the experimental XPS data.