Abstract: Mo/USYsamples,prepared by conventional impregnation with(NH₄)₆Mo₇O₂₄solution and calcined at 300,400,500,600℃,were characterized,by XRD,XPS, ²⁹Si MAS NMR and ²⁷AlMASNMR,acidity measurement with IR-TPDand NO chemisop tion.The results obviously show that Mo incorporation induces an aluminium extraction from the framework of zeolite.When molybdenum is dispersed over the support at low calcination temperature(<400℃),it mainly extracts aluminium of Si(2Al)in the framework of USYzeolite. However,sintering at a high calcined temperature,molybdenum mainly extracts aluminium of Si(1Al) from the framework.There are two steps in the process of sintering of molybdenum in Mo/USY catalysts. First, molybdenum makes USY zeolite dealuminate sharply and destroy the framework,and then immediately forms bulk Al₂(MoO₄)₃with the non-framework aluminium originated from the framework of USYzeolite.

Key words: Mo/USY, Dealumination of USY, Sintering of Mo