Catalytic activity of heteropoly acids(salts) for ammoximation of cyclohexanone

Four heteropoly acid(salts) were synthesized and characterized by FT-IR. The catalytic activity of the synthesized heteropoly acids(salts) and their supported catalysts for the ammoximation reaction of cyclohexanone were estimated. The effects of the catalyst dosage, reaction temperature, reaction time, the dosage of H2O2 and NH3, solvent type on the conversion and cyclohexanone oxime selectivity of cyclohexanone ammoximation over phosphotungstic acid were investigated. The results revealed that all the four heteropoly acids possessed the Keggin-type structure and better catalytic activity in the ammoximation reaction of cyclohexanone with water as solvent, in which phosphotungstic acid was the best. Under the reaction conditions of m(H3PW12O40)/ m(C6H10O)=0.3, n(H2O2)/ n(C6H10O)=1.6, n(NH3)/ n(C6H10O)=3.0, 20°C, 5 h, the cyclohexanone conversion and cyclohexanone oxime selectivity of the cyclohexanone ammoximation reached 90.88% and 98.38%, respectively. Under the same reaction conditions as above mentioned the supported phosphotungstic acid catalysts also showed better catalytic activity in cyclohexanone ammoximation, in which the Al2O3-supported phosphotungstic acid catalyst was the best one with cyclohexanone conversion of 87.60% and cyclohexanone oxime selectivity of 97.45%.