Rutile-type metal (Cr, V) niobates as catalysts for propane ammoxidation to nitriles: In situ characterization and operando reactivity

Rutile-type Cr/Nb and V/Nb mixed oxides were prepared by co-precipitation from ethanolic solutions, and calcination at 700 °C. The development of the rutile structure during the thermal treatment of the precursor was investigated by in situ TP–Raman spectroscopy. It was found that graphite-like carbon deposits build-up during calcinations in inert. Their decomposition provides the reducing agent that leads to the formation of rutile VNbO4 at relatively mild conditions. Rutile Cr and V niobates were tested as catalysts for the ammoxidation of propane, under both hydrocarbon-rich and hydrocarbon-lean conditions. Catalysts were active but non-selective to acrylonitrile. The catalyst modifications occurring during reaction were followed by operando Raman–GC methodology. VNbO4 transforms into a catalyst active and selective for acetonitrile under leaner hydrocarbon feed.