采用共沉淀法制备了一系列Bi-Zn复合氧化物催化剂并将其用于催化苯氨基甲酸甲酯(MPC)分解制备苯基异氰酸酯(PI).用热重、X射线衍射和傅里叶变换红外光谱考察了Bi/Zn摩尔比和焙烧温度对催化剂物相结构和表面性质的影响.结果表明,Zn的加入使Bi_2O_3由α晶相转变为活性更高的β晶相,500℃焙烧时Bi-Zn前驱体分解较为完全,析出Bi_2O_3粒子的同时伴生较多Bi_(7.65)Zn_(0.35)O_(11.83)晶相.在Bi/Zn摩尔比为2/1,焙烧温度为500℃条件下制得的催化剂活性最高,此时MPC转化率为86.O%,PI选择性为91.7%,优于单独使用Bi_2O_3时的催化性能.
A series of Bi-Zn composite oxide catalysts were prepared by coprecipitation and used for the synthesis of phenyl isocyanate (PI) by catalytic decomposition of methyl N-phenyl carbamate (MPC). The effects of Bi/Zn molar ratio and calcination temperature on the phase structure and surface properties of the catalysts were investigated by X-ray diffraction, thermogravimetry, and Fourier transform infrared spectroscopy. The addition of Zn can make the crystalline of Bi_2O_3 change from a phase to β phase with better activity. The Bi-Zn precursor was almost completely decomposed at 500℃ to form Bi_2O_3 particles and more Bi_(7.65)Zn_(0.35)O_(11.83)phase. The catalyst with a Bi/Zn molar ratio of 2/1 and the calcination temperature of 500℃ exhibited the highest activity. The MPC conversion and the selectivity for PI were 86.0% and 91.7%, respectively, which was better than the activity of Bi_2O_3 used alone.
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