Ti-MWW分子筛上烯丙醇环氧化制环氧丙醇

 以哌啶为模板剂, 硼酸为结构承载助剂,采用动态水热法成功地合成了Ti-MWW层状前体,经酸处理和煅烧后,得到Ti-MWW分子筛. 紫外-可见光谱表明, Ti-MWW层状前体中含有四面体和八面体配位的钛物种. 酸处理可以很容易地将非骨架的八面体钛脱除,煅烧后分子筛不含锐钛矿相; 未经酸处理直接煅烧,部分八面体钛会聚集形成锐钛矿相. Ti-MWW层状前体的红外光谱在960 cm-1处没有骨架钛的特征吸收谱带出现,经酸处理后,该特征吸收峰出现. 以H2O2为氧化剂,考察了Ti-MWW分子筛上的烯丙醇环氧化性能,发现凝胶Si/Ti=20, 15%HNO3处理12～16 h的情况下,制得的Ti-MWW的催化性能最好,在温度为333 K和反应时间为30 min, 转化率为88.7%, 选择性为99%; 但酸处理时间过长可使部分Ti-MWW中的钛生成锐钛矿相,从而导致催化剂活性下降.

Epoxidation of Allyl Alcohol to Glycidol on Ti-MWW Molecular Sieves

Ti-MWW was prepared by acid treatment and calcination on a lamellar precursor which was synthesized under dynamic hydrothermal crystallization conditions using piperidine as a template, and boric acid as a stucture-supporting agent. The crystallization time is shortened by adding Ti-MWW seeds and increasing stirring rate. Ultraviolet-visible spectra show that the precursor contains tetrahedral and octahedral Ti species. Calcination of the precursor results in a partial condensation of the octahedral Ti to form the anatase phase. The octahedral Ti species belong to a kind of extraframework Ti, which can be removed easily by the acid treatment in a short time. The calcined Ti-MWW contains the anatase when the acid-treated time is too long. The characteristic infrared band at 960 cm^-1 is not observed for the Ti-MWW precursor, but it appears in the samples treated by acid. Epoxidation of allyl alcohol with H2O2 on Ti-MWW was studied. Ti-MWW with Si/Ti ratio of 20 and acid treatment for 12-16 h is more effective. The conversation of allyl alcohol is 88.7 %, and the selectivity for glycidol is 99% under the reaction conditions of 333 K and 30 min, but the catalytic activity of Ti-MWW decreases when the acid-treated time is too long.