介孔材料在烯烃环氧化中的催化应用

本文综述了介孔材料在烯烃环氧化反应中的应用,包括材料的制备方法、催化性能以及活性中心的表征。通过硅钛原子的合理匹配可以达到四配位钛的高度分散,从而提高催化活性。硅烷化处理增加材料表面的疏水性,能够大幅度提高活性和选择性。通过多种谱学和分子模拟等手段可表征骨架钛及其配位情况。     

介孔材料在烯烃环氧化中的催化应用

本文综述了介孔材料在烯烃环氧化反应中的应用,包括材料的制备方法、催化性能以及活性中心的表征。通过硅钛原子的合理匹配可以达到四配位钛的高度分散,从而提高催化活性。硅烷化处理增加材料表面的疏水性,能够大幅度提高活性和选择性。通过多种谱学和分子模拟等手段可表征骨架钛及其配位情况。     

The nature of the surface of pyrogenic titanium dioxide according to the optical spectroscopy data

The coordination state of titanium atoms on the surface of P25 two-phase pyrogenic titanium dioxide (Degussa) was studied by electron diffuse reflectance spectroscopy. Various methods for processing the complex electronic diffuse reflectance spectrum were considered, and two variants that could be used to obtain both qualitative and quantitative characteristics of titanium-oxygen polyhedra were suggested. Coordination structures characteristic of anatase and rutile were simultaneously present on the surface of P25. The ratio between them (54: 46) substantially differed from that determined by X-ray diffraction.     

Studies on Ziegler-Natta catalysts. Part IV. Chemical nature of the active site

The determination of the number of sites active in the polymerization of ethylene on the surface of α-TiCl₃–Al(CH₃)₃ dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α-TiCl₃ which constitutes 95% of the total surface. The results strongly favor the lateral faces of α-TiCl₃ as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal–carbon bond. The study of catalysts derived from TiCl₃CH₃ leads to the conclusion that a Ti? C bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl₃ and AlR₃. Survival of titanium–alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler-Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers.     

Functional Groups on the Surfaces of Solids

Atoms or groups foreign to the structure of a solid are often bonded to its surface. On diamond, graphite, and even silicon dioxide, the foreign atoms are bonded covalently, whereas the bonding of the structural groups to titanium oxide and alumina is predominantly ionic. Oxides are normally covered with a monomolecular hydroxide layer. Changes in the valence of the metal atoms lead to changes in the acidity of the surface; for example, reduction of surface Ti⁴⁺ions gives the surface of TiO₂ an acidic nature.     

Atomic Defects on the Surface of Quasi Two-Dimensional Layered Titanium Dichalcogenides: Stm Experiment and Quantum Chemical Simulation

The atomic surface structure of layered dichalcogenide 1T-TiSe₂ is studied by scanning tunneling microscopy (STM) at room temperature. In STM images, the ordered structures in the form of 6 ×6 ×6 triangles of Se atoms extending for 0.3 ±0.20 Å above the crystal surface are observed. The effect of a series of different atomic structural defects on the surface topology of titanium disulphide is modeled on the example of isostructural and isoelectronic 1T-TiS₂ system using the DFTB method. It is determined that a good agreement with the STM experiment is showed by the model of local 1T-TiS₂ packing defects, where the coordination of titanium atoms changes from the octahedral to the prismatic one. For these systems, the calculation results of the electronic structure and defect formation energy are also presented.     

TiO2在水及丙二醇介质中表面电性质的研究

0引言 固体颗粒在液相介质中的分散是基础研究领域和工业技术部门普遍遇到的问题 ?在化学工业领域,如涂料 ? 染料 ? 油墨 ? 化妆品等,固体颗粒的分散及分散稳定性直接影响着产品的质量和性能 ?TiO 2 颗粒的水基分散体系广泛应用于涂料 ? 油墨以及化妆品中,也是陶瓷制备过程中重     

Modelling of substitutional defects in the structure of Ti-bearing hibonite

A local atomic structure around titanium positions in Ti-bearing hibonite (CaAl₁₂O₁₉) has been studied. The structural models of substitution of different substitution defects Ti–Al in hibonite by titanium atoms have been considered. Optimization of structural models of hibonite has been done by means of density functional theory calculations using pseudopotential approximation as implemented in VASP 5.3 code. Gibbs free energies analysis has shown that models of substitution of M2 and M4 aluminum positions by titanium atoms are the most probable. For the most probable structural models of Ti-bearing hibonite theoretical X-ray absorption near-edge structure (XANES) spectra near the titanium K edge have been calculated. Significant differences in theoretical XANES spectra calculated for different structural models with non-optimized and optimized atomic structure have been demonstrated. Changes in the intensity of pre-edge structure of TiK XANES spectra for different substitution models of aluminum by titanium have been observed which relate to different titanium coordination in structural models. Energy shift of spectral features towards lower energy for optimized models implies increase of interatomic distances in local surroundings of Ti absorbing atoms.     

Structure and acid-basic properties of the surface of titanium oxides modified by phosphorus and aluminum and prepared by the alkoxo method. 2. Study of the active surface of titanium oxides

The data of temperature-programmed desorption of ammonia from the surface of oxide systems and IR spectroscopy were used to demonstrate that the strength of the surface acid sites in titanium oxides prepared by the alkoxo method and modified by aluminum decreases with respect to that in nonmodified titanium oxide. Modification of titanium oxide with P³⁺ ions from ethriol phosphite almost completely suppresses the acid properties. Modified oxides are able to chemisorb water. XANES data suggest that modification of titanium oxide with phosphorus ions increases the electron density on the titanium atoms and, correspondingly, the basicity of the materials.     

The effect of the disperse composition of a titanium catalyst on the kinetic heterogeneity of isoprene polymerization centers

The kinetic heterogeneity of centers of isoprene polymerization on fractions of titanium catalyst particles is studied. It is found that the isoprene polymerization with a catalyst consisted of particles 0.03–0.14 μm in diameter involves centers of one type with low reactivity. On catalyst particles 0.15–4.50 μm in diameter, the active centers of polymerization of two types with high reactivity may be formed. The addition of modifiers, a reduced temperature of catalyst formation, and the hydrodynamic effect result in the appearance of a narrow fraction of particles 0.15–0.18 μm in diameter with one type of surface active center that generates high-molecular-mass cis-1,4-polyisoprene. The obtained results are in accordance with the concept of particles 0.15–4.50 μm in diameter as aggregates of the elementary crystallites of β-TiCl₃ connected via additional Al-Cl bonds to surface titanium atoms. At the same time, catalyst particles 0.03–0.14 μm in diameter are formed by the minimum number of elementary crystallites, where titanium atoms are bound to a smaller number of chlorine atoms.     

Syntheses, characterizations, and single-crystal X-ray structures of soluble titanium alkoxide phosphonates

Reactions of Ti(OiPr)4 with different phosphonic acids RPO3H2 (R = Ph, 4-CNPh, Me, tBu) in organic solvents have been investigated. In the presence of small amounts of water, the new molecular titanium oxide alkoxide phosphonates [Ti4(mu 3-O)(OiPr)5(mu-OiPr)3(RPO3)3].DMSO [R = Ph (1), Me (2), tBu (3), 4-CNPh (4)] were isolated. The single-crystal X-ray structure analyses of 1 and 2 revealed hexacoordinated titanium atoms and a connectivity of (111) for each phosphonate. Under rigorous exclusion of water, the reaction of Ti(OiPr)4 with tert-butylphosphonic acid in toluene gave the titanium phosphonate tetramer [Ti(OiPr)2(tBuPO3)]4 (5). A single-crystal X-ray structure analysis of 5 revealed a 5 + 1 coordination of the titanium atoms as a result of the (112) connectivity of each phosphonate; such a coordination mode has never been reported for a titanium phosphate, phosphonate, or phosphinate. Compounds 1-5 were characterized by FT-IR, 31P MAS NMR, and solution multinuclear NMR (1H, 13C(1H,) 31P(1H)) spectroscopies. 13C CP MAS NMR experiments were carried out on arylphosphonates 1 and 4. Solution NMR experiments were also used to investigate the exchange reaction between 1 and 2 and the conversion of 5 to [Ti4(mu 3-O)(OiPr)5(mu-OiPr)3(tBuPO3)3].iPrOH by partial hydrolysis in the presence of Ti(OiPr)4. The phosphonate clusters 1-5 are soluble in organic solvents and are likely intermediates in the sol-gel processing of inorganic-organic hybrids based on titanium oxide and phosphonate groups that we are currently developing.     

离聚体分子链的络合作用对溶液性质的影响

考察了磺化丁基橡胶锌盐离聚体（Ｚｎ－ｓＩＩＲ）与苯乙烯－４－乙烯基吡啶共聚物（ＰＳＶＰ）的络合作用及其共混物溶液性质的影响，小分子含氮化合物（胺及吡啶）对Ｚｎ－ＳＩＩＲ的离子聚集体有强烈的破坏作用，表明大分子链上的锌离子能与碱性氮原了发生络合作用，Ｚｎ－ＳＩＩＲ／ＰＳＶＰ共混物粘度高于单组分溶液的粘度，这是两种分子链间存在络合作用而形成大分子交联网络的结果，根据粘度最大时所对应的组分含量，估计Ｚｎ     

Titanocene dichloride route to a tetranuclear oxo-bridged monocyclopentadienyl titanium(IV) calix[4]arene complex

Lithiation of p-tBu-calix[4]arene followed by reaction with titanocene dichloride affords a novel tetranuclear titanium(IV) monocyclopentadienyl complex, wherein a single calix[4]arene in a cone conformation provides O-phenoxy coordination to four titanium atoms, with additional mu-oxo bridging between titanium centres in an eight membered ring.     

负载型非晶态Cu／SiO2催化剂局域结构的研究

采用ＸＰＳ和ＥＸＡＦＳ方法，研究了以ｓｏｌ－ｇｅｌ法制得的超累粉体ＳｉＯ２为载体，用化学还原沉积法制备的负载型非晶态Ｃｕ／ＳｉＯ２催化剂在甲酸甲酯氢解反应前后的表面结构和局域结构。结果表明，非晶态样品中的铜原子以零价铜的形式存在，但配位数却大幅度地低于铜樯档，意味着铜原子在高比表面超细ＳｉＯ２载体上处于高分散的非晶状态，表面悬空键显著增多，表面能增大，导致配位键收缩。     

Relations between structure, acidity, and activity of WOx/TiO2: influence of the initial state of the support, titanium oxyhydroxide, or titanium oxide

Two series of WO(x)/TiO(2) catalysts, containing W surface densities up to 4.4 W atoms/nm(2), were prepared by pore volume impregnation of two different supports, titanium oxyhydroxide (amorphous) or titanium oxide (crystallized, 100% anatase). The influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performances were examined. The texture and structure of the catalysts were investigated by Brunauer-Emmett-Teller measurements, X-ray diffraction (XRD), and Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of titanium oxide, XRD and Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. CO and lutidine adsorption, followed by infrared spectroscopy, showed an increase in the strength and abundance of Br?nsted acid sites (measured after lutidine desorption at 573 K) with the W surface density above a threshold of 1.3 W atoms/nm(2). The development of Br?nsted acidity correlated with the evolution of the infrared bands attributed to polymerized W species. A direct relationship was observed between the concentration of Br?nsted acid sites and the catalytic activity for 2-propanol dehydration. Catalytic activity, for n-hexane isomerization, appears to be associated with the presence of highly condensed W species. The catalysts synthesized by impregnation of titanium oxyhydroxide exhibited a comparable behavior. Hence, for a given W surface density, the W surface structure, concentration of Br?nsted acid sites, and catalytic performances were similar. Thus, no significant effect of the initial form of the support (titanium oxyhydroxide versus titanium oxide; 100% anatase) was evidenced.     

Synthesis and molecular structures of some new titanium(IV) aryloxides.

The coordination chemistry of model phenolic ligands (pyrocatechol, salicylic acid, and 2,2'-biphenol) that are able to form respectively five-, six-, or seven-membered rings with titanium(IV) alkoxides is investigated. With pyrocatechol, a polynuclear complex containing 10 Ti atoms was characterized with a not very common doubly bridging mu3-(O,O,O',O') coordination mode. With salicylic acid, a monomeric tris(chelate) complex was obtained. With 2,2'-biphenol, a polynuclear complex containing six Ti atoms was obtained showing both mu2-(O,O') and mu2-(O,O,O') coordination modes for the ligands. Intermolecular interactions in the solid state for these three new compounds are also quantitatively discussed using the partial charge model.     

Surface Coordination of Black Phosphorus for Robust Air and Water Stability

A titanium sulfonate ligand is synthesized for surface coordination of black phosphorus (BP). In contrast to serious degradation observed from the bare BP, the BP after surface coordination exhibits excellent stability during dispersion in water and exposure to air for a long period of time, thereby significantly extending the lifetime and spurring broader application of BP.     

The importance of attractive three-point interaction in enantioselective surface chemistry: stereospecific adsorption of serine on the intrinsically chiral Cu{531} surface

Both enantiomers of serine adsorb on the intrinsically chiral Cu{531} surface in two different adsorption geometries, depending on the coverage. At saturation, substrate bonds are formed through the two oxygen atoms of the carboxylate group and the amino group (μ3 coordination), whereas at lower coverage, an additional bond is formed through the deprotonated β-OH group (μ4 coordination). The latter adsorption geometry involves substrate bonds through three side groups of the chiral center, respectively, which leads to significantly larger enantiomeric differences in adsorption geometries and energies compared to the μ3 coordination, which involves only two side groups. This relatively simple model system demonstrates, in direct comparison, that attractive interactions of three side groups with the substrate are much more effective in inducing strong enantiomeric differences in heterogeneous chiral catalyst systems than hydrogen bonds or repulsive interactions.     

乙酰基萘酚钛配合物[O,O]_nTiCl_(4-n)的合成、负载及催化乙烯聚合反应的研究

合成一类新型非茂钛 乙酰基萘酚钛配合物 [O ,O]nTiCl4 n,该系列催化剂可在较温和的条件下催化乙烯聚合 ,其催化活性在 10 4gPE (molTi·h)左右 ;由于配合物在溶剂中存在缔合现象 ,是导致活性降低和产物分子量分布加宽 .通过将乙酰基萘酚钛配合物 [O ,O]nTiCl4 n负载到MgCl2 上 ,可以大大提高催化活性 ,使之达到 10 6 gPE (molTi·h)以上 .负载后的催化剂反应平稳 ,寿命较长 .而且反应的铝钛比较低 ,并可以使用烷基铝作助催化剂 .负载催化剂所得的聚合物分子量要高于均相所得聚合物分子量 ,且分子量分布变窄 .用粉末X 衍射考察了负载催化剂的结构 .通过X 射线光电子能谱的分析 ,考察负载前后钛、镁、氯元素的电子结合能变化对催化乙烯聚合活性的影响 .     

Chemical physics of dispersed material surfaces

Adsorption and chemisorption processes involving hydroxy groups and coordinated water molecules on the surface of silica are discussed on the basis of information derived from infrared spectra, ESCA and thermogravimetric data. The formation of strongly adsorbed surface complexes is described in terms of changes in coordination number of silicon atoms and the concomitant lowering of surface tension.