Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B2O3/TiO2-ZrO2

Pure TiO2, ZrO2 and TiO2-ZrO2 mixed oxides with various compositions were prepared by the co-precipitation method. Catalysts containing 12 wt.% boria were prepared using these oxides and their catalytic performance for vapor-phase Beckmann rearrangement of cyclohexanone oxime to E-caprolactam was determined. With increasing zirconia content in the mixed oxide, the specific surface area and the temperature of the phase transformation increased; maximum values were obtained for a mixed oxide having a Ti and Zr molar ratio of 1/1. XRD results indicated that TiO2-ZrO2 became amorphous after calcination at 500degreesC if neither the content of TiO2 nor that of ZrO2 was less than 25%. The yield of lactam increased with increasing zirconia content in mixed oxide and reached a maximum value for the B2O3/TiO2-ZrO2 (1/1) catalyst. With further increase in zirconia content, the lactam yield decreased; the lowest value was observed for the pure ZrO2-supported catalyst. The acidic property and the pore characteristics of the catalyst were key factors that affected its performance. The influences of the operating parameters on the performance of B2O3/TiO2-ZrO2 (1/1) catalyst were also investigated. (C) 2002 Elsevier Science B.V. All rights reserved.