Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Synthesis, structure and physical properties of the new uranium ternary phase U3Co2Ge7

A new ternary compound, U₃Co₂Ge₇, has been synthesized from the corresponding elements by a high temperature reaction using molten tin flux. It crystallizes in the orthorhombic La₃Co₂Sn₇-type (Pearson's symbol oC24, space group Cmmm, No. 65) with lattice parameters determined from single-crystal X-ray diffraction as follows: a=4.145(2) Å; b=24.920(7); c=4.136(2) Å, V=427.2(3) Å³. Structure refinements confirm an ordered structure having two crystallographically inequivalent uranium atoms, occupying sites with dissimilar coordination. U₃Co₂Ge₇ orders ferromagnetically below 40 K and undergoes a consecutive magnetic transition at 20 K. These results have been obtained from temperature- and field-dependent magnetization, resistivity and heat-capacity measurements. The estimated Sommerfeld coefficient γ=87 mJ/mol-U K² suggests U₃Co₂Ge₇ to be a moderately heavy-fermion material.     

稀土掺杂SiO2与SiO2@Au纳米球

By using EDTA-lanthanide (Eu³⁺， Tb³⁺) coordination compound as precursor， multicolor luminescent SiO₂ nanoshperes were prepared. Also， without any pre-treatment to the surface of SiO₂ nanosphere， a facile strategy was developed for the synthesis of SiO₂@Au core-shell nanospheres.     

Ring opening of methylcyclopentane over Al2O3 and SiO2 supported Rh catalysts

Hydrogenolytic ring opening of methylcyclopentane (MCP) was investigated on Rh/Al₂O₃ and Rh/SiO₂ catalysts, prepared by the incipient wetness method. Strong dependence can be seen in the yield and distribution of ring opening products as a function of temperature and hydrogen pressure. They depended also on the support used. The ring opening reaction required high hydrogen coverage, and was not random (hindered in the vicinity of the methyl group), thus, mainly 2-methylpentane (2MP) and 3-methylpentane (3MP) were formed. The fragments consisted of C₁–C₅ alkanes, with methane andi-pentane as main fragments. This means the possibility of breaking two C−C bonds during one sojourn of the reactant on the catalyst, both taking place far from the substituent. The loose positive correlation between the ratios ofi-pentane/n-pentane and 3MP/n-hexane seems to support this conclusion. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

大尺寸TiO2/SiO2大孔材料的制备及光降解性能

先以三维骨架聚合物为整体型模板,利用硅酸酯原位溶胶-凝胶过程并结合高温烧结的方法制备出大尺寸大孔径的SiO2载体,然后通过钛酸丁酯溶液浸渍、原位水解、煅烧制备出大尺寸的TiO2/SiO2大孔材料并用SEM、TEM、FTIR、XRD和XPS对其表征,结果表明SiO2载体具有三维连续的超薄层,TiO2以纳米薄层方式均匀地沉积在SiO2的三维超薄层上,形成TiO2/SiO2/TiO2三层夹心结构,层与层界面存在Si-O-Ti键,同时复合结构提高了TiO2由锐钛矿相向金红石相的转变温度.以甲基橙为目标降解物考察不同条件下制备的复合材料的光催化活性,采用复合材料吸入甲基橙溶液的方式,并借助甲醇萃取手段研究光降解动力学过程.结果表明,该复合材料具有较好的光降解催化活性,当焙烧温度为600℃和TiO2的负载量为54.5wt%时,其活性最大且降解速率常数达到1.78 h-1.     

微乳法制备纳米TiO2 /SiO2的结构及光催化研究

Nanosized TiO₂ and TiO₂/SiO₂ particles were prepared by hydrolysis of tetrabutyl titanate (TBOT) and tetraethyl orthosilicate (TEOS) in the TX-100 reverse microemulsion. These particles were characterized by TG-DSC, XRD, FTIR, TEM，N₂ adsorption-desorption. Their photocatalytic activity was tested by degradation of methyl orange. The result shows that TiO₂/SiO₂ nanoparticles are with a monodispersed spherical phase and a uniform size distribution，and TiO₂ particles are dispersed on the surface of SiO₂. The band for Ti-O-Si vibration in FTIR was observed, the Ti-O-Si bond increased the stability of anatase TiO₂, suppressed the phase transformation of titania from anatase to rutile. And due to the addition of SiO₂, the average size of titania decreased from 38 nm in pure TiO₂ to 5 nm in TiO₂/SiO₂. It was found, under UV light irradiation, TiO₂/SiO₂ particles showed higher activity than pure TiO₂, and TiO₂/SiO₂(1/1) particles showed the highest photocatalytic activity on the photocatalytic decomposition of methyl orange, which was influenced by crystal structure, particle size, crystallinity and Surface area Characteristics.     

共沉淀法和模板法制备均匀负载CeO2/ SiO2的研究

CeO2是三效催化剂(简称TWC)中被广泛应用的涂层材料[1],其优良的储放氧能力(OSC)可以扩大TWC的工作窗口,并可以在与γ-Al2O3的相互作用中提高Al2O3的高温稳定性[2]。在高温下,CeO2会因晶粒迅速长大而失去储放氧能力。为了提高CeO2的高温抗烧结能力,以及进一步提高其氧化还原能力,大部分研究者选择了在CeO2晶格中掺入其他离子的方法,如:Zr4 、Pr3 、La3 等[3￣5],这些离子在CeO2晶格中引入了晶格缺陷,不但稳定了结构,而且提高了氧传输能力。SiO2具有很高的化学稳定性、高比表面及高热稳定性,是载体的理想选择。研究表明,CeO2负载…     

SiO2负载氮掺杂TiO2可见光响应光催化剂的制备及性能

以四氯化钛为钛源,尿素为氮源,采用液相水解-沉淀法制得SiO2负载N掺杂TiO2可见光响应TiO2-xNy/SiO2光催化剂(TSN)。以苯酚为模型物,考察了TSN在可见光区、紫外光区及太阳光下的光催化活性,以及催化剂的使用寿命、分离性能。采用XPS、FTIR、UV-Vis DRS、XRD、TEM和低温氮物理吸附等对催化剂的结构进行表征。结果表明,N以阴离子形式进入TiO2体相并置换晶格中的O,适量N掺杂的TSN在紫外光区、可见光区及太阳光下均表现出较高的活性。SiO2与TiO2界面间有Ti-O-Si键形成,结合牢固。N掺杂在TiO2表面生成Ti-O-N键,形成新的能级结构,使催化剂的吸收红移至450~500 nm,诱发TiO2可见光催化活性。SiO2负载可减小TiO2颗粒平均尺寸,增加催化剂比表面积;同时SiO2负载还可改善催化剂的分离性能,提高催化剂使用寿命。     

Mn-Na2WO4/SiO2催化剂表面活性中心结构的DFT研究

Mn Na2WO4/SiO2 is one of the best catalysts for oxidative coupling of methane.To investigate the nature of active centers and the reaction mechanism,the structure of possible metal sites formed by tungsten and manganese over the silica surface were studied using molecular simulation method and ab initio DFT calculations.Silica support exists in the catalyst as 岐瞔ristobalite and its (111) face exposes preferentially to the surface.The calculated results show that tungsten interacts with the silica surface by three or one bridge oxygen atoms to form tetrahedral [WO4],and manganese interacts with single bridge oxygen to form dispersed [MnO4] or exists as oxide clusters.The nature of the molecular orbitals and the electronic structure suggest that the tetrahedral [WO4] site with single bridge oxygen is the most probable active center responsible for methane activation.     

The release of TiO2 and SiO2 nanoparticles from nanocomposites

There is a growing interest in the development of nanocomposites consisting of organic polymers and TiO₂ or amorphous SiO₂ nanoparticles. These nanoparticles may be released from nanocomposites. There is evidence that amorphous SiO₂ and TiO₂ nanoparticles can be hazardous. Thus, in the design of nanocomposites with such nanoparticles, hazard reduction extending to the full nanocomposite life cycle would seem a matter to consider. Options for hazard reduction include: changes of nanoparticle surface, structure or composition, better fixation of nanoparticles in nanocomposites, including persistent suppression of oxidative damage to polymers by nanoparticles, and design changes leading to the release of relatively large particles.     

Selective water sorbents for multiple applications, 7. Heat conductivity of CaCl2?SiO2 composites

In this communication we present experimental data on the low temperature heat conductivity of a consolidated bed made of the CaCl₂/SiO₂ composite material measured by the “hot wire method”. The conductivity appears to increase strongly with a raise of the sorbed water amount and reaches 0.53 W/m K at a high water content when the bed is completely saturated with the salt solution. λ values obtained appear to be much higher than those for zeolite 4A, which is a competitor solid adsorbent proposed for sorption cooling and heating machines. Finally, the influence of the thermal conductivity on the specific power of sorption heat pump based on the “CaCl₂/SiO₂-water” pair is briefly discussed.     

Hydrogenation of Benzonitrile on Sn-Pt/SiO2 Catalysts Prepared by Introducing SnEt4 to Pt/SiO2: Role of Tin

Liquid phase hydrogenation of benzonitrile was studied over Sn-Pt/SiO₂ catalysts prepared by introducing tetraethyl tin onto the 3 wt.% Pt/SiO₂ catalyst. Tin content of the catalysts ranged from 0.05 to 0.63 wt.%, whereas Sn/Pt surface atomic ratios determined by chemisorption measurements were between 0.1 to 3.5. Dibenzylamine selectivity influenced to a small extent by the level of conversion and the Sn/Pt ratio wasca. 75 %. The addition of tin to Pt in the range of (Sn/Pt)_surface = 0.50–1.25 led to an increase in the turnover frequency (TOF) by a factor of 2. TOF showed a maximum at a surface atomic ratio of Sn/Pt = 1. The enhancement of catalyst activity upon the addition of tin is explained by the formation of Sn⁺-Pt ensemble sites on the surface of bimetallic nanoclusters. It is suggested that highly dispersed positively charged tin species, by polarizing the triple bond, enhance the reactivity of the -CN group. Calcination at 300°C followed by re-reduction of the catalysts resulted in a monotonic decrease of specific activity with increasing Sn/Pt ratio.     

TiO2 / SiO2核 / 壳结构复合粒子的组装及其电化学性能

TiO₂ coated SiO₂ materials as anode for lithium-ion batteries were synthesized via an in situ hydrolysis of tetraethyl orthosilicate under ultrasonic irradiation using nanometer-sized TiO₂ colloids as precursors. The XRD patterns indicate that the as-prepared core/shell particles remain anatase after calcining below 800 ℃. TEM observation shows that the particle size of TiO₂ / SiO₂ composites is ca. 200 nm, and a homogeneous SiO₂ layer is coated on the surfaces of TiO₂ particles. FTIR spectra demonstrate that SiO₂ could have been coated on the surfaces of TiO₂ particles via a chemical bonding. In addition, the first specific charge and discharge capacities of the coated particle electrode were 66.4 mAh·g^-1 and 90.7 mAh·g^-1, respectively, which indicates that the TiO₂ / SiO₂ particles are more stable than the monodispersed TiO₂. Meanwhile, the new material has good lithium intercalation-deintercalation performances.     

Characterization of Cu-ZnO-Cr2O3/SiO2 catalysts and application to dehydrogenation of 2-butanol to 2-butanone

The Cu-ZnO-Cr₂O₃/SiO₂ catalysts were prepared by impregnation method, which exhibited high activity for the dehydrogenation of 2-butanol to 2-butanone. These catalysts were characterized by means of XRD, EPR and BET. The experimental results indicated that (i) the valence states of copper play a key role, (ii) groups of copper atoms were the main active sites in this reaction, and (iii) copper oxide would lead to the condensation product of 5-methyl-3-heptanone.     

Pressure induced phase transformation in U2O(PO4)2

The high pressure behavior of U₂O(PO₄)₂ has been investigated with the help of Raman scattering and X-ray diffraction measurements up to ∼14 and 6.5 GPa, respectively. The observed changes in the Raman spectra as well as the X-ray diffraction patterns suggest that U₂O(PO₄)₂ undergoes a phase transition at ∼6 GPa to a mixture of a disordered ambient pressure phase and a new high pressure phase. The new phase resembles the triclinic mixed-valence phase of uranium orthophosphate (U(UO₂)(PO₄)₂). On release of pressure the initial phase is not retrieved.     

Pressure-induced phase transitions in Al2(WO4)3

The high pressure behavior of aluminum tungstate [Al₂(WO₄)₃] has been investigated up to ∼18 GPa with the help of Raman scattering studies. Our results confirm the recent observations of two reversible phase transitions below 3 GPa. In addition, we find that this compound undergoes two more phase transitions at ∼5.3 and ∼6 GPa before transforming irreversibly to an amorphous phase at ∼14 GPa.     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.     

High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5

Phase transitions in MgAl₂O₄ were examined at 21-27 GPa and 1400-2500 °C using a multianvil apparatus. A mixture of MgO and Al₂O₃ corundum that are high-pressure dissociation products of MgAl₂O₄ spinel combines into calcium-ferrite type MgAl₂O₄ at 26-27 GPa and 1400-2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al₂O₃ corundum and a new phase with Mg₂Al₂O₅ composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg₂Al₂O₅ phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å³, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O₆ octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O₆ octahedra. The structure is related with that of ludwigite (Mg, Fe²⁺)₂(Fe³⁺, Al)(BO₃)O₂. The molar volume of the Mg₂Al₂O₅ phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al₂O₃ corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl₂O₄ among various A²⁺B³⁺₂O₄ compounds.     

吸附法制备CuO-Ag/SiO2纳米复合物

利用吸附法原位制备CuO/SiO2、CuO-Ag/SiO2纳米复合物,研究了不同吸附质体系中预负载的纳米Ag粒子对CuO的影响。结果表明:Ag粒子对CuO的影响因吸附质的不同而不同。以Cu(Ac)2为吸附质,纳米Ag几乎没有影响;以NaOH为吸附质,纳米Ag使得CuO的晶粒粒径增大。这一结果与铜物种对Ag晶粒粒径的影响规律完全不同。通过比较不同吸附质的吸附行为,Cu(OH)2与硅胶表面的相互作用被认为是导致这一现象的原因。