Evidence for the participation of lattice nitrogen from vanadium aluminum oxynitrides in propane ammoxidation

The participation of the nitrogen from the lattice of a series of vanadium aluminum oxynitride catalysts (VAlONs) during propane ammoxidation to acrylonitrile was made evident by temporal analysis of products (TAP) at 773 K in the absence of NH3 and O2. Moreover, the influence of the presence of gaseous oxygen and/or gaseous ammonia on the catalytic performance of this new catalytic material was studied. Propane conversion increases in the presence of O2, but it is not affected by NH3. Propene and acrolein are also formed from propane in the absence of O2 and are intermediates towards acrylonitrile. In the absence of NH3 and O2, the acrylonitrile yield increases with nitrogen content for the same V/Al ratio and decreases with increasing V/Al ratio at constant nitrogen content. Propene yield decreases with nitrogen content and with increasing V/Al ratio. Almost no influence of either nitrogen content or V/Al ratio on the CO2 yield is observed. The presence of oxygen increases the CO2 yield at the expense of acrylonitrile and, even more so, of propene. Ammonia does not influence the product distribution in the absence of O2. The amount of acrolein formed is almost constant, regardless of nitrogen content, V/Al ratio, and reactant mixture, but vanishes when mixed oxides rather then oxynitrides are used. Single-pulse experiments performed with labeled ammonia confirmed the participation of lattice nitrogen in the ammoxidation.