Local environment of vanadium in V/Al/O-mixed oxide catalyst for propane ammoxidation: Characterization by in situ valence-to-core X-ray emission spectroscopy and X-ray absorption spectroscopy

The local environment of vanadium in V/Al/O amorphous oxide catalyst has been studied under propane ammoxidation reaction conditions. In situ valence-to-core X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) at the V K-edge showed that acrylonitrile production starts when vanadium in the bulk structure of the oxide material changes its formal oxidation state from +4.8 to +3.8 ± 0.1. Exposure of the catalyst to pure NH3 at 500 °C leads to further reduction of vanadium. Valence-to-core XES has also proved that the level of bulk nitridation of vanadium in the active catalyst was rather small. XPS analysis performed ex situ after the catalytic tests confirmed the presence of significant amounts of N3−, NHx, and –NN– species on the catalyst surface. It can be concluded that activation of V/Al/O catalyst on-stream is mainly associated with reduction of vanadium in the bulk structure of the material and nitridation of vanadium atoms on the surface.

Ammoxidation of propaneC3H8+2O2+NH3→C3H3N+4H2OC3H8+2O2+NH3→C3H3N+4H2OIn situ valence-to-core X-ray emission and X-ray absorption spectroscopies at V K-edge of V/Al/O catalysts showed that their activation on-stream was associated with reduction of vanadium in the bulk structure and nitridation only on the surface.Figure optionsDownload high-quality image (59 K)Download as PowerPoint slide