B_2O_3/TiO_2-ZrO_2催化环己酮肟气相Beckmann重排反应研究 Ⅳ.TiO_2-ZrO_2组成的影响

Study on Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime over B_2O_3/TiO_2-ZrO_2 Catalyst Ⅳ. Effect of Composition of TiO_2-ZrO_2

采用共沉淀法制备了不同组成的复合氧化物TiO2 ZrO2 .N2 吸附和差热分析结果表明 ,随着TiO2 ZrO2 中TiO2 含量的增加 ,其BET比表面积和晶化温度提高 ,并均在TiO2 含量为 5 0 %时达到最大值 .以TiO2 ZrO2 为载体的B2 O3 /TiO2 ZrO2 催化剂对环己酮肟气相Beckmann重排反应的催化性能表明 ,随着TiO2 ZrO2 中TiO2 含量的增加 ,己内酰胺的收率逐渐升高 ,当TiO2 含量增加至 5 0 %时 ,收率达到最大值 (96 7% ) ,之后随着TiO2 含量的进一步增加 ,己内酰胺的收率逐渐降低 .

The TiO 2 ZrO 2 mixed oxides with various TiO 2 contents were prepared by the co precipitation method and characterized by N 2 adsorption, differential thermal analysis (DTA) and X ray diffraction (XRD). It was observed that with increasing titania content in the mixed oxides, the specific surface area and the temperature of the phase transformation increased and reached maximum values at a TiO 2 content of 50%. XRD results indicated that the mixed oxides were poorly crystalline in nature after calcination at 500 ℃. The B 2O 3/TiO 2 ZrO 2 catalysts containing 12%B 2O 3 were prepared using these mixed oxides as supports and characterized by N 2 adsorption and temperature programmed desorption of ammonia. It was found that with increase in titania content in the mixed oxides, the pore size distribution of the B 2O 3/TiO 2 ZrO 2 catalysts became broader and shifted to high values, and the acid strength of the catalysts decreased. The catalytic performance of the B 2O 3/TiO 2 ZrO 2 catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime to ε caprolactam was measured at 101 kPa and 300 ℃. The results revealed that the conversion of cyclohexanone oxime increased with increasing titania content in the mixed oxides and a maximum ε caprolactam selectivity was obtained over the B 2O 3/TiO 2 ZrO 2 catalyst having a TiO 2 content of 50%. With further increase in titania content, the selectivity for ε caprolactam decreased. The difference in catalytic performance of the B 2O 3/TiO 2 ZrO 2 catalysts with various compositions of TiO 2 ZrO 2 was ascribed mainly to their different distributions of acid site strength and pore size.