不同介质中热处理TS-1的表征及催化性能

Characterization and Catalytic Performance of TS-1 after Heat Treatment in Different Media

分别以水汽和空气为介质对TS 1进行热处理 ,并采用XRF ,XRD ,FT IR ,UV Vis,2 7AlMASNMR ,2 9SiMASNMR ,3 1PMASNMR和NH3 TPD等手段对TS 1热处理后骨架结构变化及B酸中心和酸量变化进行了分析 .以丙烯环氧化反应为探针 ,考察了酸中心变化对TS 1催化性能的影响 .结果表明 ,TS 1中的微量铝随着热处理温度的升高而减少 ,导致B酸中心数量及总酸量减少 ,环氧丙烷选择性提高 ,以水汽为介质热处理时脱铝更明显 .热处理温度达到 75 0℃时 ,TS 1分子筛中的硅氧四面体发生变化 ,不同的介质对骨架钛产生不同的影响 .

The structure and surface acidity of TS-1 were adjusted by heat treatment, in order to increase its selectivity for propylene oxide (PO) in epoxidation of propylene with H2O2. The TS-1 samples, treated at different temperatures (540, 650 and 750 degreesC) in the presence of different media(vapor or air), were characterized by XRF, XRD, FT-IR, UV-Vis, MAS NMR and NH3-TPD, to determine the changes of their framework structure, surface acid sites and total amount of acid. Using propylene epoxidation as a probe, the influence of the treatment conditions on their selectivity for PO was investigated. The results show that, with the treatment temperature increasing, the Bronsted acid sites and the total amount of acid decrease obviously, the selectivity for PO, especially over TS-1 sample treated at 750 degreesC in the presence of vapor, increases from 29% to 56%, while the catalytic activity remains constant. The amount of framework aluminum in TS-1 has changed after heat treatment, it decreases with treatment temperature increasing, especially in the presence of vapor. It can be concluded that the decrease in surface acidity of TS-1 is due to the removal of framework aluminum when TS-1 was treated at high temperature; while the decrease in surface acidity of TS-1 leads to the selectivity for PO increase. The Si-O tetrahedron is partly destroyed at high temperatures, and the framework titanium may convert into non-framework titanium, which further can be sintered to form anatase TiO2. The decrease in the amount of non-framework titanium in the presence of vapor shows that the presence of vapor favors to remove non-framework titanium of TS-1.