Catalytic Ammoximation of Ketones or Aldehydes Using Titanosilicates

Microporous titanosilicates with unique crystalline structures and multi-pore systems serve as efficient catalysts for the liquid-phase ammoximation of a variety of ketones and aldehydes with hydrogen peroxide and ammonia to selectively produce corresponding oximes. The catalytic properties of ammoximation closely depend on the topology, porosity, and Ti active site of the selected titanosilicates. Titanosilicates with different topology structures exhibit distinct solvent effects. Chemical modifications (fluorination, ion-exchange with alkali cations, hydrophobicity improvement, organic amine ligand coordination, etc.) precisely tune the microenvironment of Ti sites and then effectively enhance their ammoximation performance. Controlled alumination or constructing protective mesosilica over titanosilicate's crystal surface can retard desilication in basic reaction media, effectively prolonging the duration of ammoximation processes. The ammoximation demonstrates to take place with hydroxylamine as an intermediate. Titanosilicate-based catalytic ammoximation technologies have found a wide range of applications in industrial processes for the clean production of cyclohexanone oxime and methyl ethyl ketone oxime. Bifunctional catalytic ammoximation systems are possibly constructed by implanting precious metal nanoparticles or species into titanosilicates, which are useful for the catalytic tandem oxidation reactions featured by process intensification.