Cu/SiO2催化剂制备方法对其草酸二甲酯催化氢解性能的影响

以化学吸附水解法、蒸氨法和浸渍法制备了Cu/SiO2催化剂, 并用于草酸二甲酯氢解制备乙二醇的反应. 发现用化学吸附水解法制备的催化剂具有最高的催化活性和乙二醇选择性, 乙二醇得率可达92.6%. 对还原前后不同方法制备的催化剂进行表征发现, 浸渍法制备的催化剂中Cu物种不能很好地得到分散, 因此活性较差. 蒸氨法和化学吸附水解法能较好地分散Cu物种. 由于化学吸附水解法制备的催化剂的Cu0表面积较蒸氨法的大, 且Cu＋表面积相当, 故活性高于蒸氨法制备的催化剂.     

溶胶凝胶法制备的Cu/SiO2催化剂及其催化草酸二甲酯加氢反应

采用溶胶凝胶法制备了用于草酸二甲酯加氢合成乙二醇的Cu/SiO2催化剂,在优化的反应条件下,当催化剂中Cu含量为15%～25%时,草酸二甲酯转化率和乙二醇选择性分别达到99.9%和95.0%.通过N2吸附-脱附、透射电镜、X射线衍射、氢气程序升温还原、N2O滴定法和X射线光电子能谱等手段对各Cu/SiO2催化剂进行了表...     

Formation of SnO2 Supported Porous Membranes

In this work, the effect of the substrate microstructure on the formation of SnO₂ membranes and of the sintering conditions on their porosity have been analysed. Samples have been prepared by colloidal suspensions cast on alumina or kaolin substrates. Supported membranes have been characterized by Hg porosimetry, MEV, XRD and N₂ adsorption-desorption isotherms. The results show that the narrower pore size distribution of alumina substrate allowed to prepare membranes more homogeneous and free of cracks than that supported on kaolin. The crystallite and pore sizes of the membranes could be controlled by adjusting the temperature of sintering, allowing materials with adequate microstructure with application for ultrafiltration process.     

Cu/SiO2催化剂的制备、表征及其对草酸二乙酯加氢制乙二醇的催化性能

用沉淀沉积法和不同加料顺序制备了一系列草酸二乙酯气相加氢制乙二醇的Cu/SiO2催化剂,考察了反应温度、反应压力及氢气/草酸二乙酯摩尔比对催化性能的影响,以优化催化剂的制备方法和反应工艺条件.通过TPR,XRD,BET,HRTEM和SEM对催化剂进行了表征,揭示催化剂的稳定性、成型和活性位的分布.通过对实验数据的分析,确定了最佳的制备方法、铜负载量、还原温度和反应工艺条件,使草酸二乙酯的转化率和乙二醇的收率分别达到94.8%和76.0%.     

Thermal decomposition of Me3SnO2PCl2, Me2Sn(O2PCl2)2 and Ph3SnO2PCl2

TG and DTA studies on Me₃SnO₂PCl₂, Me₂Sn(O₂PCl₂)₂ and Ph₃SnO₂PCl₂ were carried out under dynamic argon atmosphere. The results show that the decomposition proceeds in different stages leading to the formation of Sn₃(PO₄)₂ as a stable product. This compound was characterized by IR spectroscopy. Decomposition schemes involving reductive elimination reactions were proposed.     

Catalytic Performance and Texture of TEOS Based Cu/SiO2 Catalysts for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Highly active and selective Cu/SiO₂ catalysts for hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG) were successfully prepared by means of a convenient one-pot synthetic method with tetraethoxysilane( TEOS) as the source of silica. XRD, H₂-TPR, SEM, TEM, XRF and N₂ physisorption measurements were performed to characterize the texture and structure of Cu/SiO2 catalysts with different copper loadings. The active components were highly dispersed on SiO₂ supports. Furthermore, the coexistence of Cu⁰ and Cu⁺ contributed a lot to the excellent performance of Cu-TEOS catalysts. The DMO conversion reached 100% and the EG selectivity reached 95% at 498 K and 2 MPa with a high liquid hourly space velocity over the 27-Cu-TEOS catalyst with an actual copper loading of 19.0%(mass fraction).     

Preparation and Optoelectronic Property of a SnO2/CdS Nanocomposite Based on the Flowerlike Clusters of SnO2 Nanorods

A SnO₂/CdS nanocomposite based on the flowerlike clusters of SnO₂ nanorods was prepared and characterized with x-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and EDX analysis. The SEM and TEM images show the nanocomposite is composed of CdS nanoparticles and flowerlike clusters of SnO₂ nanorods. The UV–vis spectrum of the nanocomposite displays a new absorption band in the region of 350 to 530 nm, compared with that of the flowerlike clusters of SnO₂ nanorods. The measurement of optoelectronic property indicates that the photoresponse of the composite is extended into the visible region and the incident photon-to-current conversion efficiency (IPCE) of the composite is up to 6.5 in the range of 400 to 440 nm. These phenomena ought to be ascribed to the special nanostructure of the SnO₂/CdS composite obtained.     

Patterning Effect of a Sol-Gel TiO2 Overlayer on the Photocatalytic Activity of a TiO2/SnO2 Bilayer-Type Photocatalyst

TiO₂ films with a thickness of 75 ± 5 nm (anatase) were formed on SnO₂-film (580 ± 80 nm) coated soda-lime glass substrates (SnO₂/SL-glass) by a sol-gel method. Although the photocatalytic activity for CH₃CHO oxidation (_ex > 300 nm) significantly exceeded that of a standard TiO₂/quartz sample, it decayed with illumination time (t) at t > 0.75 h. Stripes of anatase TiO₂ films of 40 nm in thickness and 1 mm in width were prepared on the SnO₂/SL-glass substrate in a 1-mm pitch by photolysis of an organically modified sol-gel film. The TiO₂ patterning further increased the photocatalytic activity by a factor of 4.1 as compared to the non-patterned sample, and it was also maintained at 0 < t < 2 h. The flat band potentials of the TiO₂ and SnO₂ films are determined to be –0.34 and +0.07 V (vs. SHE), respectively, at pH = 7 by the Mott-Schottky plots. On the basis of the results, the outstanding patterning effects could be rationalized in terms of the vectorial charge separation at the interface between TiO₂ and SnO₂.     

Thermodynamic study of alcohol on SnO2 (100)-based gas nano-sensor

Alcohol dehydrogenation and condensation reactions are involved in chain growth pathways of SnO₂. These pathways lead to the formation of acetaldehyde and other products with high selectivity. It is recognised that together with the atmospheric oxygen, the presence of humidity greatly influences gas detection. Accordingly, it is important to understand the role of alcohol vapours in the sensing mechanism. Interaction between alcohol molecules and SnO₂ is investigated using MNDO method by semi-empirical calculations. We study the structural, total energy, thermodynamic properties of absorption of CH₃OH and C₂H₅OH on SnO₂ at 298?K. When exposed to ethanol, the SnO₂-based sensors showed oxidation products consisting of acetaldehyde, ethyl acetate and CH₄?+?CO. All the geometry optimisation structures were carried out using the Gaussian program package. Density functional theory optimised intermediates and transient states. The results show a sensitivity enhancement in resistance and capacitance when ethanol is near the surface, so converted into different products.     

以乙二醇为电子给体在CuO/TiO2上光催化分解水制氢

采用浸渍、热分解的方法在TiO₂纳米颗粒上负载CuO制备得到光催化剂CuO/TiO₂。研究了以乙二醇为电子给体,在CuO/TiO₂上光催化分解水制氢的反应过程。重点分析考察了影响光催化产氢速率的因素如CuO的负载量、反应时间、光催化剂用量、乙二醇初始浓度等,同时对光催化制氢的反应机理进行了初步探讨。结果表明,氙灯光源模拟太阳光下最佳产氢速率达到604.5μmol·h^-1·g^-1;CuO/TiO₂催化剂改善了光吸收性能、减少了光生载流子的复合速率,CuO可以起到传输电子的作用;乙二醇为电子给体很可能经过羟基乙醛进一步被氧化。     

以乙二醇为电子给体在CuO/TiO2上光催化分解水制氢

采用浸渍、热分解的方法在TiO₂纳米颗粒上负载CuO制备得到光催化剂CuO/TiO₂。研究了以乙二醇为电子给体,在CuO/TiO₂上光催化分解水制氢的反应过程。重点分析考察了影响光催化产氢速率的因素如CuO的负载量、反应时间、光催化剂用量、乙二醇初始浓度等,同时对光催化制氢的反应机理进行了初步探讨。结果表明,氙灯光源模拟太阳光下最佳产氢速率达到604.5 μmol·h^-1·g^-1;CuO/TiO₂催化剂改善了光吸收性能、减少了光生载流子的复合速率,CuO可以起到传输电子的作用;乙二醇为电子给体很可能经过羟基乙醛进一步被氧化。     

Synergistic Catalysis of SnO2/Reduced Graphene Oxide for VO2+/VO2+ and V2+/V3+ Redox Reactions

In spite of their low cost, high activity, and diversity, metal oxide catalysts have not been widely applied in vanadium redox reactions due to their poor conductivity and low surface area. Herein, SnO₂/reduced graphene oxide (SnO₂/rGO) composite was prepared by a sol–gel method followed by high-temperature carbonization. SnO₂/rGO shows better electrochemical catalysis for both redox reactions of VO²⁺/VO₂⁺ and V²⁺/V³⁺ couples as compared to SnO₂ and graphene oxide. This is attributed to the fact that reduced graphene oxide is employed as carbon support featuring excellent conductivity and a large surface area, which offers fast electron transfer and a large reaction place towards vanadium redox reaction. Moreover, SnO₂ has excellent electrochemical activity and wettability, which also boost the electrochemical kinetics of redox reaction. In brief, the electrochemical properties for vanadium redox reactions are boosted in terms of diffusion, charge transfer, and electron transport processes systematically. Next, SnO₂/rGO can increase the energy storage performance of cells, including higher discharge electrolyte utilization and lower electrochemical polarization. At 150 mA cm⁻², the energy efficiency of a modified cell is 69.8%, which is increased by 5.7% compared with a pristine one. This work provides a promising method to develop composite catalysts of carbon materials and metal oxide for vanadium redox reactions.     

From Adsorbent to Photocatalyst: The Sensitization Effect of SnO2 Surface towards Dye Photodecomposition

Semiconductor photocatalysis is considered one of the most promising technologies for water purification from toxic organic dyes. However, to reliably evaluate the possibility of using a given material as a photocatalyst, it is crucial to investigate not only the photocatalytic activity but also its affinity towards various dyes and reusability. In this work, we studied the adsorptive/photocatalytic properties of hollow-spherical raspberry-like SnO₂ and its SnO₂/SnS₂ heterostructures that were obtained via a chemical conversion method using three different concentrations of a sulfide precursor (thioacetamide). The adsorptive/photocatalytic properties of the samples towards cationic rhodamine B (RhB) and anionic indigo carmine (IC) were analyzed using uncommon wall zeta potential measurements, hydrodynamic diameter studies, and adsorption/photodecomposition tests. Moreover, after conducting cyclic experiments, we investigated the (micro)structural changes of the reused photocatalysts by scanning electron microscopy and Fourier-transform infrared spectroscopy. The obtained results revealed that the sensitization of SnO₂ resulted not only in the significantly enhanced photocatalytic performance of the heterostructures, but also completely changed their affinity towards dyes. Furthermore, despite the seemingly best photocatalytic performance, the sample with the highest SnS₂ content was unstable due to its (micro)structure. This work demonstrates that dye adsorption/desorption processes may overlap the results of cyclic photodecomposition kinetics.     

Electronic Structure of Fullerenelike Molecules Based on TiO2, SnO2, and SnS2

Quantum-chemical modeling of electronic structure and interatomic interaction parameters has been performed for a series of fullerenelike cage molecules based on the isoelectronic TiO₂, SnO₂, and SnS₂. The above characteristics are analyzed in relation to the type of atomic configuration, as well as the size and chemical composition of a nanostructure.     

Chemisorbed Oxygen Species over the (110) Face of SnO2

The electronic states of chemisorbed oxygen species on the (110) face of SnO₂ and their variations caused by heat treatments and/or O₂ exposure have been investigated. The reactivities of the chemisorbed oxygen species for methane oxidations were also examined.Four different chemisorbed oxygen species (O₂ ^2-, O_2-, O^-, O_b) were observed, in addition to the lattice oxygen (O^2-), on the surface of the stabilized (110) surface of SnO₂ after O₂ exposure. The O_b species was assumed to be the bridging oxygen at the topmost layer of the SnO₂ (110) surface having no neighboring oxygen vacancies. The electronic state of O_b was converted to O^- upon CH₄ exposure at 473 K by coupling with newly produced vacancies at the bridging site of the SnO₂ (110) surface.     

Microcalorimetric Studies of the Surface Reactivity of Pollutant Gas Atmospheres on Supported SnO2 and Ga2O3 Catalysts

The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry. The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide and also ammonia were measured on these catalytic surfaces. NH₃, SO₂, NO₂ are strongly adsorbed while NO is only physisorbed. The supported Ga₂O₃ samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of SnO₂ decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify the acidity of titania. In all cases, the basicity, probed by SO₂ adsorption, is very strongly affected by the deposition of Ga₂O₃ or SnO₂. The differential heats of NO₂ adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and of the amount of guest oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

EXAFS and XRD Study of the Structural Evolution during Isothermal Sintering of SnO2 Xerogels

The formation of an ordered (crystalline) phase during isothermal sintering of SnO₂ monolithic xerogels, at 200, 250, 300, 400, 500, 600 and 700°C, has been analyzed by the combined use of EXAFS and XRD techniques. For the desiccated gel (110°C), EXAFS results show the formation of small microcrystallites with the incipient cassiterite structure. Between 110 and 250°C, the dehydratation reaction leads to an amorphization evidenced by a decrease of the long and short range crystallographic order. It is due to fissure formation in the xerogel network. For higher temperatures, a continuous coagulation of the crystallites occurs, leading to grain growth. Grain and pore growth obeys the same kinetic relation, so that the microstructure grows by simple enlargement while its morphology is static.     

Comparison of the performances of Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2, and Nb/BDD anodes on electrochemical degradation of azo dye

In this paper, the preparation conditions of antimony-doped SnO₂ and PbO₂ electrode were optimized for the degradation activity of AO7 dye solution. The results showed that when the doping content of Sb is 8 mol %(SnO₂-Sb(0.08)), the SnO₂ electrode exhibited best activities for the decolorization and mineralization of AO7. The concentration of NaF in electroplating solution had a noticeable effect on PbO₂ electrode for the decolorization of AO7 solution, but little influence on the COD removal rate. The anodic stability tests showed that the electrode prepared in the solution containing 0.10 g l⁻¹ NaF (PbO₂-F(0.10)) was best for environmental application. The comparison of SnO₂-Sb(0.08), PbO₂-F(0.10) and Boron-doped Diamond (BDD) electrodes revealed that a more rapid decolorization rate was obtained on SnO₂-Sb(0.08) and PbO₂-F(0.10) electrodes in dilute AO7 solutions, while higher COD removal rate of concentrated AO7 solutions was on BDD and SnO₂-Sb(0.08) electrodes. The effect of concentration of Na₂SO₄ on the degradation rate of AO7 was very notable on BDD electrode for its highest overpotential of oxygen evolution reaction. In the chloride-containing medium, the decolorization was accelerated greatly but the completed mineralization of AO7 was inhibited with the increasing of chloride ions concentration when these high-overvoltage anodes were used Published in Russian in Elektrokhimiya, 2008, vol. 44, No. 7, pp. 865–875. The text was submitted by the authors in English.     

Surface Modification of Chitosan Films-Grafting Ethylene Glycol Oligomer and Its Effect on Protein Adsorption

This work is a part of a series on surface modification of materials made of chitosan. This report focused on grafting monomethoxy ethylene glycol oligomers (mPEG) on the surface of chitosan films. The chemical reactions were performed by immersing the films in organic solvent containing aldehyde derivative of mPEG. The presence of ethylene glycol moieties was determined by attenuated total reflectance-infrared spectroscopy (ATR-IR) and nuclear magnetic resonance (NMR). The hydrophobicity of the modified surface, determined by air-water contact angle, decreased when the ethylene glycol derivatives were grafted on the film. The modified films were also subjected to protein adsorption study in order to assess their uses in biomedical applications. It was found that the presence of ethylene glycol units reduced the adsorption of proteins (albumin and lysozyme) on the films. We therefore have shown that manipulation of the interaction between chitosan and bio-macromolecules is possible by chemically modifying the surface of chitosan.     

Effect of Ethylene Glycol on the Molecular Organization of H2O in Comparison with Methanol and Glycerol: A Calorimetric Study

Excess partial molar enthalpies of ethylene glycol, H ^E _EG, in binary ethylene glycol–H₂O, and those of 1-propanol, H ^E _IP, in ternary 1-propanol–ethylene glycol (or methanol)–H₂O were determined at 25°C. From these data, the solute–solute interaction functions, H ^E _EG–EG = N(H ^E _EG/n _EG) and H ^E _1P–1P = N(H ^E _1P/n _1P), were calculated by graphical differentiation without resorting to curve fitting. Using these, together with the partial molar volume data, the effect of ethylene glycol on the molecular organization of H₂O was investigated in comparison with methanol and glycerol. We found that there are three concentration regions, in each of which the mixing scheme is qualitatively different from the other regions. Mixing scheme III operative in the solute-rich region is such that the solute molecules are in a similar situation as in the pure state, most likely in clusters of its own kind. Mixing scheme II, in the intermediate region, consists of two kinds of clusters each rich in solute and in H₂O, respectively. Thus, the bond percolation nature of the hydrogen bond network of liquid H₂O is lost. Mixing scheme I is a progressive modification of liquid H₂O by the solute, but the basic characteristics of liquid H₂O are still retained. In particular, the bond percolation of the hydrogen bond network is still intact. Similar to glycerol, ethylene glycol participates in the hydrogen bond network of H₂O via-OH groups, and reduces the global average of the hydrogen bond probability and the fluctuations inherent in liquid H₂O. In contrast to glycerol, there is also a sign of a weak hydrophobic effect caused by ethylene glycol. However, how these hydrophobic and hydrophilic effects of ethylene glycol work together in modifying the molecular organization of H₂O in mixing scheme I is yet to be elucidated.