ZrO_(2)-Al_(2)O_(3)复合氧化物催化反应精馏合成碳酸二甲酯

ZrO_(2)-Al_(2)O_(3) composite oxide for synthesis of dimethyl carbonate in catalytic reactive distillation

采用共沉淀法制备了一系列不同Al_(2)O_(3)含量的ZrO_(2)-Al_(2)O_(3)复合氧化物,并在催化精馏实验装置中考察了该催化剂在碳酸丙烯酯(PC)与甲醇酯交换制备碳酸二甲酯(DMC)过程中的催化性能。通过X射线衍射(XRD)、红外光谱(FTIR)、X射线光电子能谱(XPS)、CO_(2)程序升温脱附(CO_(2)-TPD)和NH_(3)程序升温脱附(NH_(3)-TPD)等手段对所制备的催化剂进行了表征。结果表明,催化剂表面存在的酸碱性位点是制约PC与甲醇酯交换性能的重要因素。复合氧化物中Al_(2)O_(3)含量可以有效调控催化剂的结构特征和表面的酸碱性质,不同于Zr O_(2)或Al_(2)O_(3)单金属催化剂,复合氧化物Zr O_(2)-Al_(2)O_(3)在合成过程中形成了稳定的固溶体结构,导致催化剂表面弱酸量增加,并产生了强碱位点。数据分析表明,催化剂表面的强碱和弱酸含量高时,其催化活性高,说明该反应具有酸碱协同催化作用。当Zr/Al比为1时,弱酸和强碱量均达到最大值,PC的转化率和DMC选择性可达到98.14%和99.96%。催化剂在经过12次循环使用后依旧保持较高的活性,具有良好的结构稳定性。

A series of ZrO_(2)-Al_(2)O_(3) composite oxides with different Al2O3 contents were prepared by coprecipitation method.Then,the catalytic performance of these catalysts in the process of transesterification of propylene carbonate(PC)and methanol to synthesize dimethyl carbonate(DMC)was investigated in the catalytic distillation experiment.The catalysts were characterized by XRD,FTIR,XPS,CO2-TPD and NH3-TPD.The results show that the presence of acid-base sites on the catalyst surface is the key factor for the restriction of the transesterification of PC and methanol.Different from ZrO2 or Al2O3 single metal catalysts,the synthesized ZrO_(2)-Al_(2)O_(3) catalysts form a stable solid solution structure.The amount of weak acid increased and strong base sites were produced on the catalyst surface.Data analysis shows that when the content of strong base and weak acid on the surface of the catalyst is high,its catalytic activity is high,indicating that the reaction has a synergistic catalytic effect of acid and base.When the Zr/Al ratio is 1,the contents of weak acid and strong base reach the maximum level,and the conversion and DMC selectivity of PC can reach 98.14%and 99.96%.After 12 cycles of recycling,the catalyst still has high activity and presents remarkable good structural stability.