液相酸溶液后补钛合成Ti-MWW分子筛

首先在含钠体系硼酸与哌啶用量较少的条件下水热合成B-MWW分子筛前驱体, 然后对其进行液相酸溶液后补钛, 合成了高结晶度的Ti-MWW分子筛. 利用粉末X射线衍射、 氮气吸附-脱附分析、 紫外-可见漫反射光谱和紫外拉曼光谱等技术考察了硅钛比、 温度等后补钛参数对所合成Ti-MWW分子筛的织构性质、 钛物种周围配位环境及催化1-己烯环氧化性能的影响, 确定适宜液相后补钛的硅钛比为30, 温度为373 K. 并且发现, 在后补钛体系中添加少量氟化铵可显著提高所合成Ti-MWW分子筛对1-己烯环氧化的催化活性. 本研究不仅证实了酸处理Ti-MWW分子筛前驱体的脱硼补钛机制, 也为Ti-MWW分子筛的合成提供了一种新的方法与思路.     

Ti-MWW催化烯丙基氯环氧化高效合成环氧氯丙烷

 研究了具有MWW结构的新一代钛硅分子筛Ti-MWW催化剂对烯丙基氯液相环氧化高效合成环氧氯丙烷的催化性能. 结果表明, Ti-MWW的催化活性以及产物选择性均优于传统的钛硅分子筛TS-1. 对于Ti-MWW,合适的溶剂为非质子性溶剂丙酮和乙腈,在该溶剂中环氧化物不易发生溶剂化开环反应; 而对于TS-1,合适的溶剂是质子性溶剂甲醇,但甲醇可导致醇醚副产物的生成. 在Ti-MWW催化剂上烯丙基氯的转化率和环氧氯丙烷的选择性都能达到99%以上.     

含钛CDS-1分子筛的水热合成与表征

以钛酸正丁酯（TBOT）为钛源、以发烟硅胶为硅源、以四甲基氢氧化铵（TMAOH）为模板剂,采用了一步法直接水热合成了CDO晶体结构的含钛分子筛,Ti-CDS-1。用粉末X-射线衍射、电子扫描、紫外可见漫反射光谱,傅立叶变换红外光谱等手段对所合成的样品进行了表征,结果表明,Ti-CDS-1维持原来全硅分子筛的片状晶体外形;原料中钛原子大部分嵌入到CDS-1分子筛分子筛骨架,少量钛在分子筛表面形成八面体非骨架钛物种,这部分骨架外钛可以用酸处理选择性去除。     

以钛酸四丁酯和四氯化钛混合物作钛源合成钛硅分子筛TS—1

以四丙基溴化铵（TPABr)作模板剂、氨水作碱源,以四氯化钛部分取代钛酸四丁酯作钛源,成功地合作了钛硅分子筛TS－1。用XRD、IR、UV－Vis等手段进行表征的结果显示,样品呈现MFI拓扑结构特征。同经典合成体系的TS－1相对比,在紫外谱图上,样品中未出现锐钛矿TiO2的特征吸收,证明混合钛源更有利于钛原子进入分子筛骨架内,合成的分子筛样品在丙烯环氧化反应中也表现出了优异的催化性能。     

TS-1分子筛的无机法合成及其催化苯酚羟基化性能

以无机固体硅胶和硫酸钛为原料,利用无机盐在多孔载体表面自发分散的基本原理,通过热处理先形成具有类似于钛硅分子筛Si-O-Ti键的无机SiO2-TiO2前驱体,然后以四丙基氢氧化铵为模板剂,通过水热晶化成功合成了TS-1分子筛.X射线衍射、傅里叶变换红外光谱和紫外-可见光谱表征表明,SiO2-TiO2前驱体中钛主要呈高分散状态,其中高分散的钛在水热晶化过程中基本进入了TS-1分子筛骨架,而以锐钛矿相存在的钛则基本不变.当SiO2-TiO2前驱体处理温度为450℃,SiO2/TiO2摩尔比为40,晶化温度为160～170℃,晶化时间为48～72h时,合成的TS-1分子筛对苯酚羟基化反应的催化活性最好,与经典有机法合成的TS-1分子筛的催化活性相当.     

Ti-MWW/H2O2体系催化官能化烯烃环氧化

研究了Ti-MWW/H2O2催化体系对多种官能化烯烃液相环氧化的催化性能.结果表明,与钛硅分子筛TS-1相比,Ti-MWW具有更高的催化活性和环氧化产物选择性.溶剂对Ti-MWW催化环氧化反应的活性影响较大,其中水是催化丙烯酸乙酯和乙酸烯丙酯的最佳溶剂,随着C=C双键相邻官能团吸电子能力的增强,环氧化反应的催化活性下降.     

四氯化钛气固相反应法制备钛硅分子筛机理的研究

采用气固相法使TiCl₄与HZSM-5高硅分子筛反应制备了钛硅分子筛Ti-ZSM-5.运用FT-IR, UV-vis, XRD, TG, ICP-AES等手段对合成的钛硅分子筛进行了表征,并以30%H₂O2水溶液环氧化氯丙烯为探针反应对合成的Ti-ZSM-5进行了催化活性考察,结果表明分子筛所载钛原子完全进入骨架,没有发现非骨架钛,Ti-ZSM-5催化性能良好. 定量分析结果表明,钛原子同晶取代铝原子反应进入骨架的贡献极小,仅占骨架钛的0.32%,钛原子主要通过TiCl₄与羟基窝反应而进入分子筛骨架.     

固定床反应器中Ti-MWW催化H2O2分解

在固定床反应器中,H2O2与Ti-MWW分子筛的接触时间越长,其分解率越高.结果表明,分子筛骨架Ti和其拥有的酸性位是造成H2O2在分子筛上分解的主要原因,非骨架Ti对H2O2分解的影响弱于骨架Ti.H2O2的无效分解直接影响反应物的转化效率.了解H2O2无效分解的原因,有利于设计出高活性钛硅分子筛.同时在固定床中研究钛硅分子筛催化分解H2O2的反应有可能成为一种评价钛硅分子筛催化活性的新方法.     

以深度脱铁Fe-YNU-1分子筛为硅源制备Al-YNU-1及其形成机理

主要研究了以哌啶为模板剂,深度脱铁的Fe-YNU-1分子筛为硅源,采用后合成法制备Al-YNU-1分子筛及其形成机理. 通过考察铝含量、水含量、晶化时间和酸处理条件对形成Al-YNU-1分子筛结构的影响规律,发现Al-YNU-1分子筛骨架中的Al含量较以深度脱硼的B-MWW为硅源得到的样品提高了近一倍. 结果表明,Si源中存在大量晶格缺陷位、酸处理脱除Al-MWW层状前驱中大部分模板剂分子与大量骨架Al是形成Al-YNU-1分子筛的必要条件.     

无机SiO2-TiO2前驱体体系合成高性能TS-1分子筛

 在热处理条件下,使Ti(SO4)2在多孔硅胶表面自发分散形成具有类似于钛硅分子筛催化活性中心结构单元的Si-O-Ti键的SiO2 -TiO2前驱体,将该前驱体在模板剂四丙基氢氧化铵的作用下水热晶化得到了钛硅分子筛TS-1. X射线衍射、红外光谱和扫描电镜表征表明, TS-1分子筛晶化完全,钛原子已进入TS-1分子筛骨架. 苯酚羟基化反应测试结果表明,前驱体的热处理温度对合成的TS-1分子筛的催化性能影响很大,处理温度以450 ℃为宜.     

A New Generation of Titanosilicate Catalyst: Preparation and Application to Liquid-Phase Epoxidation of Alkenes

A novel titanosilicate with the MWW topology, Ti-MWW, has been prepared by direct hydrothermal synthesis using boric acid as a structure-supporting agent, and also by post-incorporation of tetrahedral Ti species into MWW silicalite through controlled structural conversions between three-dimensional crystalline silicalite and the lamellar precursor. Ti-MWW is further converted by delamination into a thin sheet material applicable to the reaction of bulky reactants. Both direct hydrothermal synthesis and postsynthesis methods make it possible to introduce a controllable amount of Ti species into the MWW structure. An acid treatment of uncalcined samples is essentially important for the removal of the extraframework octahedral Ti species located on the exterior layer surface. The catalytic properties of Ti-MWW have been compared with those of conventional titanosilicates (TS-1, TS-2, Ti-Beta, Ti-MOR, Ti-MCM-41, etc.) in the epoxidation of various alkenes with hydrogen peroxide. Hydrothermally synthesized Ti-MWW proves to be more effective in the epoxidation of linear alkenes including functionalized ones, and also exhibits considerable activity for cycloalkenes. Moreover, it shows a unique shape selectivity not shared with other titanosilicates in the epoxidation of cis/trans geometric alkene isomers. Postsynthesized Ti-MWW, nearly free of boron, catalyses the alkene epoxidation more effectively as a result of the tetrahedral Ti species different from those resulting from the direct synthesis, which turns out to be the most active epoxidation titanosilicate catalyst so far. Delaminated Ti-MWW, possessing an extremely open and accessible surface area but maintaining the basic structure of zeolite, catalyses the epoxidation of various cycloalkenes more actively than large pore titanosilicates including mesoporous Ti-MCM-41.     

Anatase-TiO2 nanomaterials: analysis of key parameters controlling crystallization

Nanoparticulated TiO2 materials with anatase structure were synthesized by using a microemulsion method. The structural characteristics of the amorphous solid precursors and their evolution during thermal treatments were studied by using X-ray absorption structure (X-ray absorption near edge structure XANES and extended X-ray absorption fine structure EXAFS), XRD-PDF (X-ray diffraction-pair distribution function), and infrared spectroscopy. Concerning the precursor materials, XANES and EXAFS showed a local order closely related to that of the anatase structure but containing defective, undercoordinated Ti5c4+ species in addition to normal Ti6c4+ species. The PDF technique detects differences among samples in the local order (below 1 nm) and showed that primary particle size varies throughout the amorphous precursor series. The physical interpretation of results concerning the amorphous materials and their evolution under thermal treatment gives conclusive evidence that local, intraparticle ordering variations determine the temperature for the onset of the nucleation process and drive the solid behavior through the whole crystallization process. The significance of this result in the context of current crystallization theories of oxide-based nanocrystalline solids is discussed.     

TiCl4溶胶凝胶法制备TiO2纳米粉体

利用TiCl4的乙醇溶液作为前驱体 ,运用溶胶凝胶法制备了TiO2 纳米粉体 .研究结果表明 ,在TiCl4与乙醇混合成溶液的过程中 ,TiCl4即与乙醇及乙醇中的微量水发生醇解和部分水解脱氯反应形成钛酸酯 .在随后的成胶化过程中 ,则主要是钛酸酯吸收气氛中的水气 ,脱去乙醇基形成Ti-OH键并发生缩脱水聚合形成无机聚合物溶胶 .增加成胶化时间 ,可以促进乙醇基的脱去和无机聚合物的形成 ,促进锐钛矿TiO2 纳米颗粒的形成     

Crystallization Behavior of SiO2-TiO2 Ceramics Derived from Titanosiloxanes on Pyrolysis

The crystallization behavior of SiO2-TiO2 ceramics derived from titanosiloxanes was investigated in relation to the structure of the precursor and the pyrolysis temperature. The titanosiloxanes, [Si(OBut)2OTi(acac) 2O]2, [(ButO)3SiO] 2Ti (OPri)2, and [(ButO)3SiO] 3Ti(OPri), were pyrolyzed in an air atmosphere to form SiO2-TiO2 ceramics which crystallized to anatase at 600–650°C, 700–750°C, and 800–850°C, respectively. The crystallization temperature decreased with increased titanium content of the precursor. The average crystallite size of anatase increased with increased pyrolysis temperature and the titanium content. The crystallization temperature and the crystallite size for SiO2-TiO2 ceramics is controlled by the precursor structure, which may enable control of the physical properties of the ceramic materials.     

Unconventional Route to Oxygen-Vacancy-Enabled Highly Efficient Electron Extraction and Transport in Perovskite Solar Cells

The ability to effectively transfer photoexcited electrons and holes is an important endeavor toward achieving high-efficiency solar energy conversion. Now, a simple yet robust acid-treatment strategy is used to judiciously create an amorphous TiO₂ buffer layer intimately situated on the anatase TiO₂ surface as an electron-transport layer (ETL) for efficient electron transport. The facile acid treatment is capable of weakening the bonding of zigzag octahedral chains in anatase TiO₂, thereby shortening staggered octahedron chains to form an amorphous buffer layer on the anatase TiO₂ surface. Such amorphous TiO₂-coated ETL possesses an increased electron density owing to the presence of oxygen vacancies, leading to efficient electron transfer from perovskite to TiO₂. Compared to pristine TiO₂-based devices, the perovskite solar cells (PSCs) with acid-treated TiO₂ ETL exhibit an enhanced short-circuit current and power conversion efficiency.     

Sodium niobate adsorbents doped with tantalum (TaV) for the removal of bivalent radioactive ions in waste waters

Mesoporous silica containing a large amount of isolated Ti was prepared from an alkoxytitanosiloxane precursor through a hard template method. Isopropoxytris(tris-tert-butoxysiloxy)titanium (((i)PrO)Ti[OSi(O(t)Bu)(3)](3), TS3) was synthesized and TS3 was mixed with mesoporous carbon (CMK-3), a hard template. The mixture was pyrolyzed at 180 °C to form a composite consisting of titanosilica and the hard template. After calcination at 600 °C for the removal of the carbon template, the titanium species were not transformed to anatase TiO(2), proved by DR-UV-Vis, FTIR, XPS, and XRD, while the ESR results indicated the presence of isolated Ti. The mesoporous structure was verified by SEM, TEM, and N(2) adsorption. The Si/Ti ratio of the product was consistent with that of the precursor. All the results show that the material prepared from the precursor is ordered mesoporous silica containing a large amount of isolated Ti in the frameworks. The use of well-defined alkoxytitanosiloxane precursor leads to the formation of mesoporous silica with exactly controlled composition of titanium with neither loss of Ti nor transformation to anatase.