水合ZrO_2固载12-磷钨杂多酸催化四氢呋喃开环聚合

12-Tungstophosphoric Acid Supported on Hydrous Zirconia for Ring-open Polymerization of Tetrahydrofuran

采用过量浸渍结合溶剂蒸发将12-磷钨杂多酸(TPA)分散于水合ZrO2干凝胶表面(以TPA质量分数表示的固载量为5～65 wt%),再经120～500℃空气气氛焙烧得到水合ZrO2固载磷钨杂多酸催化剂.借助等离子体原子发射光谱(ICP-AES)、物理吸附、X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、吡啶吸附红外(Py-IR)光谱以及氨程序升温脱附(NH3-TPD)等手段对催化剂的组成、结构及酸性质进行表征,针对四氢呋喃(THF)开环聚合考察其酸催化性能.研究表明,在适宜的TPA固载量(35～45 wt%)及活化温度(120～300℃)条件下,TPA主要以畸变但结构未遭破坏的Keggin物种高度分散于水合ZrO2表面,赋予催化剂合适的酸性质及优良的催化性能.当TPA固载量过高时,部分TPA以体相物种析出;而当固载量过低或活化温度过高时,TPA的部分Keggin结构会发生分解.体相物种在THF极性体系中的严重溶脱或Keggin结构分解引起的酸性位大量丧失都使得材料的催化性能大幅度下降.催化剂重复使用实验显示,TPA固载量为45 wt%、300℃活化的催化剂具有良好的稳定性.

Ring-open polymerization of tetrahydrofuran was investigated with hydrous zirconia-supported 12-tungstophosphoric acid（TPA） as catalysts.We prepared the catalysts with TPA loading（mass fraction） of 5～65 wt% by suspending hydrous zirconia in an ethanol solution of TPA,refluxing the suspension,removing the solvent by evaporation,and then calcinating the powder at 120～500 ℃.The catalysts were characterized by ICP-AES,N2 adsorption,XRD,FTIR spectroscopy,pyridine adsorption,and NH3-TPD analysis.The experiments showed that,at the moderate TPA loading（35～45 wt%） and proper calcination temperature（120～300 ℃）,TPA on support mainly existed as highly dispersed,somewhat distorted but intact Keggin species,endowing the catalysts with proper acidity and acceptable catalytic performances.A higher TPA loading gave rise to the emergence of bulk-like TPA species,whereas a lower one or a relatively higher calcination temperature resulted in the destruction of TPA Keggin units.In these circumstances,the catalyst performances declined greatly due to either the serious leaching of TPA into the product or the comparative low acidity of the catalysts.A preliminary reusability study on catalysts with 45 wt% TPA indicated that calcination at 300 ℃ could greatly enhance the stability of the catalyst.