热扩散法制备MoO3/SiO2催化草酸二甲酯和苯酚酯交换反应

采用热扩散法（TS）和等体积浸渍法制备了MoO₃/SiO₂催化剂用于草酸二甲酯和苯酚酯交换反应.结果表明，热扩散法制备的10%MoO₃/SiO₂-TS催化剂较等体积浸渍法制备的10%MoO₃/SiO₂-C催化剂具有更好的催化性能.运用X射线衍射、Raman光谱、X射线光电子能谱分析、吡啶吸附红外光谱、NH₃程序升温脱附等手段对催化剂进行了表征，发现虽然两种方法制备的催化剂都只有弱Lewis酸中心，钼均以氧化钼单体形式存在，未形成解离和聚合，但是10%MoO₃/SiO₂-TS催化剂较10%MoO₃/SiO₂-C催化剂表面钼含量更高且MoO₃分散得更好.在苯酚用量为0.2mol，10%MoO₃/SiO₂-TS催化剂用量为1.2g，反应温度为180℃，草酸二甲酯与苯酚的摩尔比为2，反应时间为4h的优化条件下，苯酚转化率可达70.9%，甲基苯基草酸酯和草酸二苯酯的收率分别达63.1%和7.7%.

Transesterification of dimethyl oxalate with phenol over a MoO3/SiO2 catalyst prepared by thermal spreading

MoO₃/SiO₂ catalysts for the transesterification of dimethyl oxalate (DMO) with phenol were prepared by both the thermal spreading (TS) and incipient wetness impregnation methods. The results showed that the 10%MoO₃/SiO₂ catalyst prepared by TS (10%MoO₃/SiO₂-TS) exhibited higher catalytic performance compared with the 10%MoO₃/SiO₂ catalyst prepared by incipient wetness impregnation (10%MoO₃/SiO₂-C). The catalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, pyridine-IR spectroscopy, and NH₃ temperature-programmed desorption. These analyses indicated that weak Lewis acid sites were formed on the catalyst surfaces and that the Mo species were present as monomeric MoO₃ rather than as isolated molybdenum oxide or polymolybdate species on both catalysts, although the 10%MoO₃/SiO₂-TS exhibited better dispersion of MoO₃ and a higher surface Mo content than the 10%MoO₃/SiO₂-C. Under the optimal transesterification reaction conditions (1.2 g 10%MoO₃/SiO₂-TS, T=180℃, n(DMO)/n(phenol)=2, t=4 h), the conversion of phenol was 70.9%, and the yields of methyl phenyl oxalate and diphenyl oxalate were 63.1% and 7.7%, respectively.