Abstract: 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 Bi₂O₃ change from α phase to β phase with better activity. The Bi-Zn precursor was almost completely decomposed at 500 ^oC to form Bi₂O₃ particles and more Bi_7.65Zn_0.35O_11.83 phase. The catalyst with a Bi/Zn molar ratio of 2/1 and the calcination temperature of 500 ^oC 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 Bi₂O₃ used alone.

Key words: methyl N-phenyl carbamate, phenyl isocyanate, catalytic decomposition, bismuth oxide, zinc oxide;composite oxide