硅羟基对二氧化硅固载有机锡酯交换催化性能的影响

Effect of silanol content in silica support on catalytic performance of silica-anchored organotin catalyst for transesterification

采用新方法制备了二氧化硅固载有机锡。以无机Sn Cl4为锡源,在合成有机锡的同时制备有机锡硅烷试剂,再将其固载到二氧化硅上,用于碳酸二甲酯与苯酚酯交换合成碳酸二苯酯的反应。通过不同的制备方法和处理方法,制得不同硅羟基含量的二氧化硅载体;研究硅羟基对锡固载量及固载有机锡催化性能的影响。TG与ICP表征显示,锡固载量与二氧化硅载体的硅羟基含量正相关。29Si MAS NMR表征发现,制备的固载有机锡中含有较多的T2和T3物种,利于有机锡的稳定固载。二氧化硅硅羟基含量越高,催化剂的锡固载量越高,活性越好。介孔二氧化硅为载体制备的Sn-MSiO_2表现出最好的催化活性:用量1.0 g,在150～180℃反应9 h,苯酚转化率达50.4%,酯交换选择性高于99.9%;用0.5 g考察重复使用性能,重复使用5次,苯酚转化率由41.2%降低到35.0%。锡流失是活性下降的主要原因。

Silica-anchored organotin catalysts has been synthesized by a new synthetic scheme. It involves the synthesis of organotin-silane during the preparation of organotin using inorganic SnCl4 as tin precursor, which was then ahchored on the silicas for the transesterification of DMC with phenol to diphenyl carbonate. A series of silica supports containing different silanols were obtained by different preparations along with different treatments. TG and ICP characterizations showed that the Sn loading of the catalyst had positive correlation with the silanol content of the silica support. 29Si MAS NMR measurements indicated that the prepared catalysts possessed many T2 and T3 species, which was in favor of the stability. The more silanol the silica support contained, the more Sn the catalyst supported, and the more active the catalyst would be. Sn-MSiO2, the catalyst with the mesoporous silica support, exhibited the best catalytic performance： with a reaction temperature of 150-180℃ for 9 h, and a catalyst amount of 1.0 g, the phenol conversion and the transesterification selectivity reached 50.4% and 99.9%,respectively; in recycle test with a catalyst amount of 0.5 g, the phenol conversion decreased from 41.2% to 35.0% after five runs. Sn leaching was the main reason for the decline of catalytic activity.