ammoxidation

Ammoxidation is a gas-phase chemical process in which an unsaturated hydrocarbon is converted into a nitrile by the simultaneous action of ammonia and molecular oxygen over a solid oxide catalyst. In these reactions, nitrogen is supplied from NH3 while oxidation establishes the nitrile functionality; many catalysts operate via a Mars–van Krevelen mechanism in which lattice oxygen participates in substrate oxidation and is replenished by O2.

Industrially important variants include the ammoxidation of propylene to acrylonitrile and of butadiene to adiponitrile, both of which provide key monomers for polymers. Aromatic substrates such as toluene can also be ammoxidized to benzonitrile. Substrates are typically alkenes or dienes, and products are nitriles such as acrylonitrile, adiponitrile, or benzonitrile.

Catalysts are usually mixed oxide systems. For acrylonitrile, bismuth phosphate-type catalysts have historically been used; for adiponitrile, Mo–V–Te–Nb–O–type catalysts are common. Operating conditions are high temperature (roughly 350–500 C) and moderate pressures, with feed gas containing NH3 and O2 alongside the hydrocarbon. Catalyst composition, feed ratios, and reactor design determine selectivity toward nitrile over undesired oxidation to CO2 or NOx.

Industrial relevance: acrylonitrile is a major precursor for polymers and fibers, and adiponitrile is a precursor for nylon-6,6. Safety considerations include managing the exothermic heat of the process, handling ammonia, and controlling byproducts and emissions.