The Synthesis of Adamantane over PW/SiO_2 Catalyst

12-tungstophosphoric acid(PW) was immobilized on silica dioxide at room temperature to form the PW/SiO2 catalysts.The physical and chemical properties of the PW/SiO2 catalysts were characterized by X-ray diffraction(XRD),N2 adsorption and temperature programmed desorption of ammonia(NH3-TPD),and the catalytic performances of prepared PW/SiO2 catalysts were evaluated by catalyzing the isomerization reaction of endo-tertrahydrodicyclotadiene(endo-TCD) to form adamantine(ADH) in a 100 mL bath stainless-steel autoclave with stirring.It was found that even if the PW loading is as high as 40%(wt),the loaded PW could still be highly dispersed on the surface of silica dioxide because of the interaction between molecular PW and pore walls of silica dioxide,thus the acidity and activity of the prepared PW/SiO2 catalysts increase with increasing the loading of PW at first and reach their maximum when the PW loading is 40%(wt),then the acidity and activity decrease with further increase of PW loading.The experiments show that,using 40% PW/SiO2 as catalyst,99.5% conversion of endo-TCD and 24.7% yield of adamantine can be obtained under following optimal conditions:activated temperature 200℃,reaction temperature 260℃,reaction time 3 h,initial pressure 1.1 MPa,the mass ratio of catalyst to endo-TCD 0.7 and the molar ratio of cyclohexane to endo-TCD 5.0.