Phosphotungstic acid encapsulated in ultra stable Y zeolite (PW-USY) was prepared by the 'ship in the bottle' synthesis.The obtained catalysts were characterized with FT-IR,ICP,UV-vis,N2-adsorption,XRD and SEM techniques.Compared with immobilized catalysts (PW/USY),it was demonstrated that encapsulation of Keggin-type 12-phosphotungstic acid in the supercage of USY zeolite was realized.In the ammoximation of cyclohexanone system with H2O2 as oxygen source,PW-USY showed better catalytic activity than PW/USY.Moreover,the catalytic performance of PW-USY did not drop apparently after using five times,and could solve the leakage problem of active component in polar reaction media better than immobilized catalysts (PW/USY).
