摘要
通过 12 0 0h模拟实验 ,考察了环己酮氨氧化水热环境对廉价法合成的大晶粒TS 1(1μm× 2 μm× 6 μm ,n(Si) /n(Ti) =5 3 6 )结构的影响 .通过XRF ,XRD ,SEM ,UV Vis,IR ,NH3 TPD和丙烯环氧化探针反应等表征手段发现 ,在环己酮氨氧化水热环境中 ,TS 1的结构不稳定 ,骨架硅易被溶解脱除 ,从而导致骨架钛脱落 .流失的骨架硅溶解于处理液中 ,而脱落的钛物种主要以硅钛碎片形式滞留在沸石表面 .氨产生的碱性是导致沸石骨架不稳定的根本原因 ;H2 O2 本身不影响TS 1的结构 ,它与氨水共存时可通过生成羟胺减轻TS 1结构破坏的程度 .硅钛碎片中的钛并非以六配位钛形式存在 ,而主要以四配位形式存在 ,并具有活化H2 O2 。
Ammoxidation of cyclohexanone in liquid phase over titanium silicate 1 (TS 1) is an environmentally benign process for producing cyclohexanone oxime. However, the TS 1 framework depletion occurs during ammoxidation. The effect of the hydrothermal environment of cyclohexanone ammoxidation on TS 1 framework was studied by simulated experiments lasting for 1?200 h. The TS 1 zeolite was previously synthesized with tetrapropylammonium bromide as template, which has crystal size of 1 μm×2 μm×6 μm and n (SiO 2) / n (TiO 2) ratio of 53 6. The simulated experiments were carried out in small glass tube fixed bed reactors placed in a water bath. The hydrothermal environment for ammoxidation was simulated by using a mixture of NH 3(7 5 mol/L)+H 2O 2 (4 0 mol/L) aqueous solution at 80 ℃. During the experiments, sampling was made at intervals and characterization was carried out with XRF, XRD, SEM, UV Vis, IR, NH 3 TPD and probe reaction of propylene epoxidation. The TS 1 framework is not stable in the ammoxidation environment, having mass loss of about 11% accompanied by pronounced decrease of Si/Ti ratio and framework Ti content, when time on stream reaches 1?200 h. The basicity of NH 3 aqueous solution is the true cause of TS 1 framework depletion, while the oxidability of H 2O 2 seems to be helpful in alleviating the basicity possibly by converting NH 3 into NH 2OH. The mass loss of TS 1 zeolite is mainly due to the dissolution of the framework Si into effluent, whereas the extracted framework Ti remains staying on the zeolite surface. The non framework Ti thus formed is not in aggregated hexahedral coordination state, but in highly dispersed tetrahedral coordination state. Such non framework Ti is active for propylene epoxidation. The mechanism of TS 1 framework depletion was discussed.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2003年第6期441-446,共6页
基金
国家重点基础研究发展规划项目 (G2 0 0 0 0 480 0 9)
关键词
钛硅沸石
TS-1
环己酮
氨氧化
水热稳定性
过氧化氢
环氧丙烷
晶体结构
骨架钛
丙烯
titanium silicate 1, crystal structure, framework titanium, hydrothermostability, cyclohexanone, ammoxidation, hydrogen peroxide, propylene, epoxidation, propylene oxide
