Chemical equilibrium controlled synthesis of polyoxymethylene dimethyl ethers over sulfated titania

The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers(DMMn) were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.     

Effects of calcining temperature on photocatalytic activity of Fe-doped sulfated titania

Using industrial titanyl sulfate as a raw material, Fe‐doped sulfated titania (FST) photocatalysts were prepared by using the one‐step thermal hydrolysis method and characterized using XRD, SEM, TGA–DSC, FTIR, UV–Vis DRS and N₂ adsorption–desorption techniques. The effects of calcining temperature on the structure of the titania were investigated. The photocatalytic activity of the FST was evaluated using the photodegradation of methylene blue and photooxidation of phenol in aqueous solutions under UV and visible light irradiation, respectively. The results evinced that Ti⁴⁺ is substituted by Fe³⁺ in titania lattice and forms impurity level within the band gap of titania, which consequently induces the visible light absorption and visible‐light‐driven photocatalytic activity. The synergistic effects of Fe‐doping and sulfation are beneficial to the efficient separation of the photogenerated carriers and also improve the quantum efficiency of photocatalysis. In addition, Brönsted acidity arisen from the strong inductive effect of sulfate is also conducive to enhancing the photocatalytic performance of FST. However, when the calcining temperature is higher than 800°C, sulfur species and surface hydroxyl groups decompose and desorb from FST and the specific surface area decreases sharply. Moreover, severe sintering and rutile phase formation occur simultaneously. All these are detrimental to photocatalytic activity of FST.     

Suppression of radical-cationic benzene oligomerization on sulfated zirconia

The effect of catalyst activation conditions on transformations of benzene cation radicals on sulfated zirconia has been studied by in situ ESR spectroscopy. After the catalyst activation at 300°C there was no oligomerization of the cation radicals to biphenyl and heavier products, which is observed after catalyst calcination at 500°C. It has been suggested that the oligomerization is suppressed by the presence of strong Br?nsted sites on the surface.     

Hydrothermal synthesis and catalytic properties of superacid sulfated titania

The micromorphology and catalytic properties of nanocrystalline TiO₂/SO₄²⁻ superacid systems prepared by a conventional sol-gel process, as well as hydrothermal (HT) and microwave-hydrothermal (MW-HT) processes, were analyzed. The samples prepared by the HT process have no developed surfaces and, as a consequence, have no high reactivity in isobutylene oligomerization. The TiO₂/SO₄²⁻ samples prepared by single-step MW-HT synthesis in their morphologic, acid, and catalytic properties are competitive with the systems prepared by the conventional multistage sol-gel process.     

Thermodynamic studies of methylene blue adsorption onto Fe-doped sulfated titania

Adsorption equilibrium of methylene blue onto Fe-doped sulfated titania (FST) samples was studied at different temperatures (298, 303, and 308 K). Based on the wavelength scanning from 580 to 760 nm, the wavelength of maximum absorbance of methylene blue was determined to be 666 nm and the corresponding calibration curve can be described by the equation of A = 0.0068 + 0.1514C. The adsorption of methylene blue onto FST samples was conformed to the Langmuir isotherms. The absorption capacity of each FST sample for methylene blue increases with increasing temperature. The increase in the adsorption parameters (q _m, b, and K ₀) and the positive ΔH ^θ reveal the endothermic feature of this adsorption process. The negative ΔG ^θ shows the adsorption of methylene blue onto FST samples can be carried out spontaneously at the examined temperatures. Furthermore, with the calcination temperature increases, the variation in crystallization degree, the surface and the sulfur species will obviously influence the adsorption properties of FST samples and the thermodynamic parameters of this adsorption process.     

含锆ZSM-5分子筛上丙烯齐聚反应的研究

以正丁胺(NBA)为模板剂，通过水热法直接合成了Zr/ZSM-5分子筛。XRD分析表明Zr/ZSM-5分子筛结晶度良好，但衍射峰的强度稍有差别。SEM显示样品分子筛表面规整，为3 μm～5 μm的棒状晶体。采用NH3-TPD法对分子筛进行了酸性测试，结果表明，在锆质量分数0.2%～1.2%，分子筛的中强酸和强酸量随锆质量分数的增加而增大，并向高温方向偏移。丙烯齐聚催化反应的活性评价结果显示，中强酸和强酸的量对Zr/HZSM-5催化性能有显著影响，在反应过程中对链的增长起促进作用。     

Influence of phosphate modification on the surface properties of sulfated titania

The effect of increasing phosphate loading on the bulk and surface properties of sulfated titania was investigated by thermogravimetry, X-ray diffraction, laser Raman spectroscopy and FT-IR spectroscopy. The acid properties of the material were probed by low-temperature FT-IR spectroscopy of adsorbed CO. Monophosphate species in varying symmetries and protonation states were detected on the surface of the sulfated titania at low loadings. These condensed with formation of surface polyphosphates with increasing loading. Phosphate blocks weak Lewis acid sites and partially displaces sulfate groups. While the acid, properties of phosphate-free sulfated titania are dominated by Lewis acid sites, the phosphated samples also developed Brønsted acid sites due to the presence of POH groups on the surface.     

Photocatalytic degradation of methylene blue and phenol on Fe-doped sulfated titania

Fe-doped sulfated titania (FST) photocatalysts with high photocatalytic activity were prepared from industrial titanyl sulfate solution and characterized using X-ray diffraction (XRD), thermogravimetry analysis?Cdifferential scanning calorimeter (TGA-DSC), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption?Cdesorption techniques. The photocatalytic activity of the FST photocatalyst was evaluated using the photodegradation of methylene blue (MB) and the photooxidation of phenol in aqueous solutions in the presence of UV irradiation, respectively. The effect of various parameters, such as calcining temperature, calcination time, initial concentration of substrate, amount of catalyst and pH value on the photocatalytic activity of FST photocatalyst was investigated. Among the parameters studied, calcining temperature, initial concentration of substrate, and amount of catalyst have a very similar effect on the activity of FST photocatalyst for both the photodegradation of MB and the photooxidation of phenol, while the others have distinct differences. The optimal calcination conditions were 500?°C, 1.5?h and 650?°C, 2.5?h; the optimal catalyst concentration were 1.0 and 1.2?g?L^?1; the optimal pH values were 8 and 4 for the photodegradation of MB and the photooxidation of phenol, respectively. In addition, the mechanism for the high photocatalytic efficiency of FST photocatalyst has also been put forward.     

Room temperature observation of p-xylylenes by 1H NMR and evidence for diradical intermediates in their oligomerization

p-Quinodimethanes (p-QDMs) are reactive molecules that have been invoked as transient intermediates in a number of reactions. Dilute solutions of benzene-based p-QDMs, p-xylylene (1), alpha-methyl-p-xylylene (10), and 2,5-dimethyl-p-xylylene (11) can be prepared by fluoride-induced elimination of trimethylsilyl acetate from the appropriate precursor. It has been found that these solutions are stable enough to allow these reactive p-QDMs to be observed by 1H NMR spectroscopy at room temperature. For the first time, the 13C NMR spectrum of p-QDM 1 was observed. After several hours at room temperature, these p-QDMs form dimers, trimers, and insoluble oligomers. Formation of trimers provides evidence that p-QDMs 1, 10, and 11 dimerize by a stepwise mechanism involving dimeric diradicals as intermediates.     

Photocatalytic hydrogen production over CuO-modified titania

Efficient hydrogen production and decomposition of glycerol were achieved on CuO-modified titania (CuO-TiO(2)) photocatalysts in glycerol aqueous solutions. CuO clusters were deposited on the titania surface by impregnation of Degussa P25 TiO(2) powder (P25) with copper nitrate followed by calcination. The resulting CuO-TiO(2) composite photocatalysts were characterized by X-ray diffraction (XRD), UV-visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), N(2) adsorption-desorption, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The low-power ultraviolet light emitting diodes (UV-LED) were used as the light source for photocatalytic H(2)-production reaction. A detailed study of CuO effect on the photocatalytic H(2)-production rates showed that CuO clusters can act as an effective co-catalyst enhancing photocatalytic activity of TiO(2). The optimal CuO content was found to be 1.3 wt.%, giving H(2)-production rate of 2061 μmolh(-1)g(-1) (corresponding to the apparent quantum efficiency (QE) of 13.4% at 365 nm), which exceeded the rate of pure TiO(2) by more than 129 times. The quantum size effect of CuO clusters is deemed to alter its energy levels of the conduction and valence band edges in the CuO-TiO(2) semiconductor systems, which favors the electron transfer and enhances the photocatalytic activity. This work shows not only the possibility of using CuO clusters as a substitute for noble metals in the photocatalytic H(2)-production but also demonstrates a new way for enhancing hydrogen production activity by quantum size effect.     

Immobilization of yttrium over crystalline titania

A co-precipitation method was adopted for the immobilization of yttrium radioactive waste over crystalline titania. A high uptake of⁹¹Y was observed over the preformed hydrous titania. Weighable quantity of Y was coprecipitated with Ti(IV) hydroxide and a maximum of 38 wt% was found to be adsorbed. Mixed masses were calcined separately at 800 and 1000°C for 20 hours, and soxhlet leach tests at 97°C, repeated 7 times at an interval of 24 hours, showed the release of yttrium in the order of 10^–1 and 10^–2 g·m^–2·d^–1, respectively. X-ray powder diffraction analysis revealed that the yttrium was immobilized in the titania crystal lattice which suffered some structural changes with the formation of new mineral phase Y₂Ti₂O₇ which is accompanied by rutile and little quantity of anatase form of titania at 800°C, and only rutile form of titania at 1000°C.     

Room temperature hydroalkylation of electron-deficient olefins: sp3 C-H functionalization via a lewis acid-catalyzed intramolecular redox event

A practical method for the intramolecular hydroalkylation of electron-deficient olefins has been developed. The direct transformation of benzylic, tertiary, and sterically hindered secondary sp3 C-H bonds into C-C bonds under the action of a catalytic amount of a variety of Lewis acids is described. The mechanism of these transformations is proposed to involve a tandem hydride transfer/cyclization sequence.     

Nano sulfated titania as solid acid catalyst in direct synthesis of fatty acid amides

Nanosized sulfated titania was prepared by a sol-gel hydrothermal process. X-ray diffraction (XRD), transmission electron, and scanning electron micrographs (TEM and SEM), FT-IR specific surface area, and BET N(2) adsorption were employed to characterize the properties of the synthesized sulfated TiO(2). The results indicate that both anatase and rutile TiO(2) are obtainable. This prepared sulfated titania showed high catalytic activity in direct amidation of fatty acids as well as benzoic acids with various amines under solvent-free conditions.     

Selective dimerization,oligomerization, homopolymerization and copolymerization of olefins with complex organometallic catalysts

Review embarrasses the problems of low molecular weight olefins (ethylene and propylene) selective oligomerization to butene-1, hexene-1, octene-1, 4-methylpentene-1; selective polymerization of olefins to obtain polymers with a given molecular mass, molecular mass distribution, branching (for the polyethylene), chain structure [atactic, iso-, syndio-, gemiisotactic, stereoblock type and containing terminal vinyl and vinylidene bonds (for polypropylene)]; “live” homo-and copolymerization of olefins, and alternating copolymerization of olefins in the presence of complex organometallic catalysts.     

Hydrosilylation of olefins over rhodium complex anchored over thioether-functionalized MCM-41

<正>The hydrosilylation of alkenes with triethoxysilane has been achieved at 120 C in the presence of 0.01 mol%of thioetherfunctionalized MCM-41 anchored rhodium complex,affording the corresponding addition products in 68-91%yields.This supported rhodium complex can be reused several times without noticeable loss of activity.Our system not only solves the basic problems of catalyst separation and recovery,but also avoids the use of phosphine ligands.     

Butane isomerization over platinum promoted sulfated zirconia catalysts

The isomerization of n-butane to i-butane has been studied at 11 bar in a microflow reactor over sulfated zirconia (SZ) and platinum containing sulfated zirconia (Pt-SZ) catalysts. In the presence of H₂ a significantly higher temperature is required for isomerization over SZ than in its absence. The rate over SZ is higher with n-butane containing 33 ppm butene as an impurity than with a feed that is pre-equilibrated over a Pt/SiO₂ catalyst to a much lower butene content. Over Pt-SZ the reaction rate is higher, because any butene consumed is rapidly regenerated; the conversion is perfectly stable in 83 h runs, selectivity to i-butane is 95%; i-pentane and propane are the main byproducts. The activation energy is 53 kJ mol⁻¹. Upon increasing the pressure of H₂ from 1.1 to 6.6 bar, the reaction rate was found to decrease in a perfectly reversible fashion. Kinetic analysis reveals that the reaction order is negative in H₂ (−1.1 to −1.3 depending on the temperature) and positive in n-butane (+ 1.3 to +1.6), indicating that the mechanism of this isomerization is intermolecular: butene is formed and reacts with adsorbed C₄-carbenium ions to adsorbed C₈ intermediates which isomerize and undergo β-fission to fragments with i-C₄ structure. This mechanism is confirmed over Pt-SZ by isotopic labelling experiments, though at much lower pressure, using double labelled ¹³CH₃---CH₂---CH₂---¹³CH₃. The primary reaction product consists of i-butane molecules, containing zero, one, two, three and four ¹³C atoms in a binomial distribution.     

低温水热法制备硅胶负载型二氧化钛催化剂

TiO2作为一种优良的光催化材料,能够降解有机物,起到抗菌防污的作用,其在工业上的潜在应用已吸引众多研究者的普遍关注和深入研究[1-3]。为了进一步提高它的光催化活性,研究者试图运用各种方法和技术对纯TiO2进行改进。负载[3]是其中常用方法之一。对于无负载的二氧化钛,由于本     

Room temperature polymerization of glycidol

Glycidol has been shown to be easily polymerized at room temperature in the presence of triethylamine, pyridine, lithium hydroxide, potassium hydroxide, sodium hydroxide, sodium methoxide, sodium amide, and other catalysts. Its reactivity with these catalysts is vastly greater than that of propylene oxide. Evidence is presented to support the structural assignment for polyglycidol and the mechanism of polymerization.     

Photoinduced oxidation of benzhydrol over lanthana modified sol-gel titania

Lanthana modified sol-gel titania is prepared through particulate sol-gel route and the physico-chemical characterizations of the prepared systems were done using X-Ray diffration, EDX, BET surface area-pore volume measurements and TG-DTG analysis. Benzophenone was observed to be the sole product in the TiO₂ photocatalyzed oxidation of benzhydrol in oxygen purged acetonitrile. The influence of various parameters, like irradiation time, amount of catalyst, concentration of the catalyst and other factors on the photocatalytic oxidation has been investigated. The proposed mechanism envisages the involvement of a superoxide radical anion.