Comparative study of synthesis of methylamines from carbon oxides and ammonia over Cu/A12O3

Methylamines have been synthesized from carbon dioxide, hydrogen and ammonia using Cu/Al₂O₃ catalysts with different copper loading. The reaction was performed in a fixed-bed micro reactor in the temperature range 473–573 K and at 0.6 MPa total pressure. The product amines were mono-, di- and trimethylamine (MMA, DMA, TMA). The distribution of the amines depended mainly on the reaction temperature and the NH₃/CO₂ ratio in the feed gas. At elevated temperatures and higher NH₃ concentrations methanol synthesis is suppressed and MMA is the main amine product, reaching a ratio of MMA:DMA:TMA of 1:0.23:0.07. Conversion and product distribution were compared to that of the corresponding reaction starting from CO or methanol instead of CO₂. With CO conversion was lower but the selectivity to MMA was higher. If CO₂ was replaced by methanol, conversion increased and TMA was the main product. In all experiments a change of space velocity had relatively little influence on both conversion and distribution of amines.     

An EXAFS study of Cu/ZnO and Cu/ZnO-Al2O3 methanol synthesis catalysts

Cu K-absorption edge and EXAFS measurements on binary Cu/ZnO and ternary Cu/ ZnO-Al₂O₃ catalysts of varying compositions on reduction with hydrogen at 523 K, show the presence of Cu microclusters and a species of Cu¹⁺ dissolved in ZnO apart from metallic Cu and Cu₂O. The proportions of different phases critically depend on the heating rate especially for catalysts of higher Cu content. Accordingly, hydrogen reduction with a heating rate of 10 K/min predominantly yields the metal species (>50%), while a slower heating rate of 0.8 K/min enhances the proportion of the Cu¹⁺ species ( 60%). Reduced Cu/ZnO-Al₂O₃ catalysts show the presence of metallic Cu (upto 20%) mostly in the form of microclusters and Cu¹⁺ in ZnO as the major phase ( 60%). The addition of alumina to the Cu/ZnO catalyst seems to favour the formation of Cu¹⁺/ZnO species.     

Prototype high-throughput system for hydrothermal synthesis and X-ray diffraction of microporous and mesoporous materials

In the hydrothermal synthesis of microporous and mesoporous materials a large number of parameters including chemical composition of the mixture, reagent sources, organic templates, temperature, and time play a role. The high-throughput experimental approach facilitates screening of this multi-parameter space for conditions favoring formation of desired zeolite phases and ordered mesoporous materials. A critical issue in the development of a high-throughput system for hydrothermal synthesis is the avoidance of cross-contamination between the individual synthesis volumes. Further important issues are automation of reactant dosing, product filtration, calcination and identification. In this work, a prototype multi-clave was designed with three 5 mL synthesis vials for operation at temperatures up to 200 °C under autogenous pressure. The multi-clave is equipped with a sample tray for filtration, washing and drying of all of the synthesis products at the same time. This multi-filter also serves as the sample holder for X-ray diffraction characterization. The innovation resides in the multi-clave concept and the integration of the entire process from synthesis over product workup to XRD characterization without necessitating individual sample transfer. The performance of the prototype was evaluated with the synthesis of the mesoporous–microporous hybrid material zeotile-2, and of clathrasils.     

Preparation of Cu/ZrO2 catalysts for methanol synthesis from CO2/H2

Cu/ZrO₂ catalysts for methanol synthesis from CO₂/H₂ were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO₂ and selectivity of methanol are higher for DP catalysts than for SP catalysts.     

Active sites in Cu/ZnO/ZrO2 catalysts for methanol synthesis from CO/H2

Among various Cu/ZnO/ZrO₂ catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO₂ obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO₂ catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO₂ catalyst with 15 wt.% of ZrO₂ turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO₂ catalysts is reduced, the Cu²⁺ species present in the ZrO₂ lattice is transformed to Cu⁺ species. This leads to the speculation that the addition of ZrO₂ to Cu/ZnO catalysts gives rise to the formation of Cu⁺ species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO₂ catalyst in addition to Cu metal particles. Consequently, the ratio of Cu⁺/Cu⁰ is an important factor for the specific activity of Cu/ZnO/ZrO₂ catalyst for methanol synthesis.     

Microwave-assisted hydrothermal synthesis and catalytic activity study of crednerite-type CuMnO2 materials

A new and "flexible" microwave-assisted hydrothermal (MWH) synthesis of crednerite CuMnO₂ materials is proposed. Single-phase compounds are synthesized by means of the MWH method in a significantly shorter time than by conventional hydrothermal heating. CuMnO₂ single-phase compounds are obtained in the 80–180 °C temperature range, with times ranging from 5 min to 1 h, starting from nitrate reactants. The structure and the phase composition were studied by X-Ray diffraction and FT-IR spectroscopy, and reveal that all samples crystallize within the crednerite structure with the C2/m space group and without other impurities. The surface area is 59.5 m²/g for the sample obtained at 120 °C, 5 min, and 76.8 m²/g for the sample obtained at 80 °C, 5 min, respectively. The morphological analysis by transmission electron microscopy revealed plate-like nanoparticles, 20–50 nm in diameter. As application, in the case of the as-obtained products the catalytic activity was tested for hydrogen evolution in aqueous sulphide solution.     

水热一步法合成SO42-/Zr-PHTS及其催化性能

在低酸度硫酸体系中,以P123(EO₂₀PO₇₀EO₂₀)为模板剂水热法一步合成硫酸化锆掺杂PHTS固体酸催化剂(SO₄^2-/Zr-PHTS),利用XRD、TEM、N₂吸附-脱附以及NH₃-TPD、Py-FTIR等手段对其进行表征。结果表明,SO₄^2-/Zr-PHTS具有有序的六方相介孔结构,具有以L酸为主的弱、中强度的酸性中心;随着硅锆摩尔比的增加,其酸量逐渐减少,比表面积逐渐增加,孔容、孔径无显著变化。SO₄^2-/Zr-PHTS在催化四氢呋喃聚合中表现出良好的反应性能,推测固体酸的表面酸性和孔结构决定着催化四氢呋喃聚合的反应性能。     

Cu/TiO_2-SiO_2催化剂的制备及糠醛选择加氢活性研究

采用溶胶凝胶-水热法制备Cu/TiO2-SiO2催化剂,并运用XRD、BET对催化剂进行表征,以糠醛选择加氢制糠醇反应为探针,考察载体组成及Cu含量对催化剂活性的影响。结果表明,载体中引入适量的TiO2能够抑制Cu晶粒的增长,改善Cu粒子在催化剂中的分散性。载体中TiO2质量分数40%,Cu负载量(质量分数)20%时,制备的Cu/TiO2-SiO2催化剂具有较好的催化活性。     

Effect of Sb addition on SbxSn1-xS thin films: The structural,morphological, and linear/nonlinear optical changes for optoelectronic applications

The current paper reports the changes in the structural and optical properties of antimony-doped tin sulfide ternary (Sb_xSn_1-xS) (x = 0, 0.05, 0.1, 0.15, 0.2) thin films synthesized by the thermal evaporation technique on a glass substrate. Structural characterization techniques such as X-ray diffraction and Raman spectroscopy of the prepared sample revealed that the thin films are crystalline in nature. The nanoflake-like structure was found from the surface morphological analysis performed by field emission scanning electron microscopy. The concentration of the compositional elements was confirmed from the energy dispersive X-ray analysis. The linear and nonlinear optical parameters were calculated by using the transmission data obtained from UV–vis spectroscopy in the range of 800–1100 nm. The optical measurements showed an increase in transmittance and shifting of the absorption edge. The optical bandgap increased (1.239–1.378 eV) and the refractive index decreased with the increase of Sb concentration, satisfying the Moss rule. The nonlinear susceptibility and the nonlinear refractive index (n₂) decreased with Sb content. The changes in both linear and nonlinear parameters by varying the antimony doping concentration could be helpful for controlling the optical properties of Sb_xSn_1-xS thin films and could be a suitable candidate for many photonics and optoelectronic applications.     

Ti_2SnC原位自生TiC_(0.5)增强Cu基复合材料的制备及压缩特性

本文以Ti_2SnC陶瓷为先驱体,利用其高温下与Cu的反应原位自生TiC_(0.5)颗粒增强Cu基复合材料并研究了其压缩特性。通过差热分析、X射线衍射和扫描电子显微镜等手段分析了Ti_2SnC与Cu的反应行为,并探讨了制备工艺对复合材料的物相组成、增强相形貌及材料特性的影响。结果表明,Ti_2SnC与Cu在900°C就开始发生反应,Ti_2SnC中的部分Sn原子逃逸扩散到Cu基体内,留下TiC_(0.5)作为增强相颗粒;随着温度的升高,反应程度加剧;当温度达到1150°C时,Ti_2SnC全部分解,形成亚微米TiC_(0.5)增强Cu(Sn)复合材料。TiC_(0.5)颗粒随保温时间增加而更加均匀地分布在基体内。对于初始Ti_2SnC体积含量为30%的TiC_(0.5)/Cu(Sn)复合材料,保温时间从0 h增加至2 h,其抗压强度和压缩变形率分别从1109 MPa±11 MPa和24.4%±0.6%增加到1260 MPa±22 MPa和28.9%±1.1%。     

利用Sol-Gel法与水热合成法制备纳米TiO2及其光催化活性研究

以Sol-Gel法及水热合成方法制备了纳米TiO2,利用XRD进行了表征,以太阳光为光源,通过对亚甲基蓝溶液的降解反应,考察了两种方法所得样品的光催化活性。结果表明,利用水热合成法制备的锐钛矿型TiO2具有更小的粒径,而通过溶胶-凝胶制得的样品为混晶型TiO2,对亚甲基蓝降解具有较高的光催化活性。     

Electrical and optical study of Cu(In, Ga)Se2 co-evaporated thin films

Co-evaporation technique from three sources was used to prepare Cu(In, Ga)Se₂ polycrystalline thin films for photovoltaic conversion. Their conductivity was studied in the range 20–300 K. The grain boundary scattering mechanism is mainly responsible for the diffusion process in the latter materials. In the low temperature region, we interpret the data in terms of Mott law and the analysis is very consistent with the variable range hopping. However, thermoionic emission is predominant at high temperatures. When the conductivity deviates from the classical grain boundary conduction models, inhomogeneity is then considered and parameters such as the standard deviation and the mean potential barrier height are derived. Transmittance measurements yielded band gap values of 1.07 and 1.64 eV for CuInSe₂ and CuGaSe₂, respectively.     

一步水热合成In2S3/CdIn2S4异质结微球及其光催化性能

利用一步水热法成功制备了In₂S₃/CdIn₂S₄异质结微球催化剂,通过降解甲基橙(MO)、酸性橙Ⅱ(AOⅡ) 和罗丹明B(RhB)来评价所制备催化剂的活性。实验结果表明,In₂S₃/CdIn₂S₄异质结微球对MO、AOⅡ和RhB的光催化降解率分别达到了87%、75%和96%,明显高于催化剂In₂S₃和CdIn₂S₄。瞬态光电流和阻抗测试结果表明,In₂S₃/CdIn₂S₄异质结微球受光激发产生的电子空穴对能快速得到分离。捕获主要活性物种实验表明,该反应体系中主要是超氧自由基和空穴起关键性作用。In₂S₃/CdIn₂S₄异质结微球催化剂重复使用四次,其催化能力依然保持较高水平。In₂S₃/CdIn₂S₄异质结微球活性的增强归因于异质结的形成有助于电子的转移,从而降低了电子空穴对的复合概率。并且合适的能带结构有助于产生大量的光生电子,电子与活性氧的结合最终引起氧化能力的增强。     

The effect of ageing time on co-precipitated Cu/ZnO/ZrO2 catalysts used in methanol synthesis from CO2 and H2

The effect of suspension ageing time during the catalyst precipitation process on the performance of co-precipitated Cu/ZnO/ZrO₂ catalysts in methanol synthesis from CO₂ and H₂ has been studied. The ageing time influenced greatly the physical and chemical characteristics of the catalysts as well as their activity in the methanol synthesis. Prolonged ageing was advantageous, mainly due to both lower sodium contents and enhanced crystallinity of the catalysts.     

Hydrothermal method for the synthesis of Sb2Te3, and Bi0.5Sb1.5Te3 nanoplates and their thermoelectric properties

In this study, a modified hydrothermal method is reported for the preparation of Sb₂Te₃ and Bi_0.5Sb_1.5Te₃ nanoplates and their bulk samples was prepared by spark plasma sintering (SPS). The crystal structure, morphology, and thermoelectric properties were investigated. The microstructure results indicate that the bulk samples consisted nanograins after SPS. The presence of nanograins, high Seebeck coefficient (181 μV/K), high electrical conductivity (763 Ω^?1 cm^?1), and low thermal conductivity (1.15 W/mK) has been achieved in Sb₂Te₃ nanoplate bulk samples. As a result, the dimensionless thermoelectric figure of merit (ZT) of 0.55 at 400 K was achieved. Moreover, the peak ZT shifted to higher temperature compared with other reported results found in literature.     

Cu／SiO2催化剂的制备及在环己醇脱氢制环己酮反应中的催化性能

采用共沉淀法制备了不同铜／硅物质的量比的Cu／SiO2催化剂,结果表明：在n（Cu）：n（si）=1：2时,DH-0．5-400催化剂在环己醇脱氢制环己酮的反应中表现出优异的催化活性。考察了不同焙烧温度对环己醇脱氢制环己酮的影响。结果表明：焙烧温度400℃时,制备的DH-0．5-400催化剂上的环己酮得率为52．9％,高于其他催化剂。采用XRD和BET对催化剂进行了表征,根据结果,在催化剂中氧化铜是以均匀、高分散的微小纳米粒子或以簇的形式存在,结果增加了与反应物的接触机会,致使DH-0．5-400催化剂显示出高的催化性能和环己酮选择性。     

Creation of the active site for methanol synthesis on a Cu/SiO2 catalyst

The effect of ZnO/SiO₂ in a physical mixture of Cu/SiO₂ and ZnO/SiO₂ on methanol synthesis from CO₂ and H₂ was studied to clarify the role of ZnO in Cu/ZnO-based catalysts. An active Cu/SiO₂ was prepared by the following procedure: the Cu/SiO₂ and ZnO/SiO₂ catalysts with a different SiO₂ particle size were mixed and reduced with H₂ at 523-723 K, and the Cu/SiO₂ was then separated from the mixture using a sieve. The methanol synthesis activity of the Cu/SiO₂ catalyst increased with the reduction temperature and was in fairly good agreement with that previously obtained for the physical mixture of Cu/SiO₂ and ZnO/SiO₂. These results indicated that the active site for methanol synthesis was created on the Cu/SiO₂ upon reduction of the physical mixture with H₂. It was also found that ZnO itself had no promotional effect on the methanol synthesis activity except for the role of ZnO to create the active site. The active site created on the Cu/SiO₂ catalyst was found not to promote the formation of formate from CO₂ and H₂ on the Cu surface based on in situ FT-IR measurements. A special formate species unstable at 523 K with an OCO asymmetric peak at ~1585 cm^-1 was considered to be adsorbed on the active site. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molten salt synthesis of BaTiO3 nanorods: Dielectric,optical properties,and structural characterizations

Single-crystalline perovskite BaTiO₃ (BTO) nanorods were synthesized by (BaTi₂O₅-template) molten salt synthesis (MSS) methods. The effects of process parameters (eg, calcination temperature, reaction time, molten salt content, as well as different phase structures of TiO₂ and barium oxides) on the formation of BTO nanorods and their structural characteristics were systematically investigated. The BTO nanorods synthesized at 800°C for 5 hours by MSS method with the molar salt ratios of BaCO₃:TiO₂ (anatase):NaCl:KCl equal to 1:1:60:60, exhibited smooth and clean surfaces through their lengths. Their diameters were in the range of 130-200 nm with average length of 5 μm. Large-scale amount of BTO nanorods was synthesized by BaTi₂O₅-template MSS method at 650°C with molar salt ratios of BaC₂O₄:BaTi₂O₅ (template):NaCl:KCl equal to 1:1:60:60. The BTO nanorods successfully retained the one-dimensional morphology of the BaTi₂O₅ templates and their lengths were in the range of 5-10 μm with an average diameter of ~300 nm. The single-crystalline nature of individual BTO nanorod was revealed by its selected area electron diffraction patterns and high-resolution TEM images. The BTO nanorods exhibited good optical properties with optical bandgaps in the range of 2.5-2.6 eV. Such optical bandgaps make the present BTO nanorods promising candidates for ferroelectric photovoltaic devices. Dielectric properties of the BTO nanorods synthesized by MSS method were comparatively investigated with the BTO nanorods synthesized by the BaTi₂O₅-template MSS method. It is found that the later BTO nanorods exhibit better dielectric properties and their synthesized temperature is also much lower than the former ones.     

Influence of Mg doping on the structural,optical, and electrical properties of Zn0.95Li0.05O Nanoparticles

This study investigates the effect of Li and Mg codoping on the structural, optical, and electrical properties of the ZnO. Zn_0.95−xLi_0.05Mg_xO (x = 0.00, 0.01, 0.02, 0.03) nanoparticles are synthesized by hydrothermal method. X-ray diffraction (XRD) results confirmed that all samples are polycrystalline with a hexagonal-wurtzite structure. The surface morphology of the samples were examined by Scanning Electron Microscopy (SEM). The SEM analysis showed that all samples exhibit cheese-like plates and the plate sizes increase with Mg addition. Optical properties were examined by UV-VIS diffuse reflectance spectroscopy. The optical measurements indicate that the reflectance edge of the samples have red shift up to 2% Mg doping level, but blue-shift for 3% Mg doping. The optical band gap of Zn_0.95−xLi_0.05Mg_xO nanostructures are calculated as 3.227, 3.214, 3.209, and 3.221 eV with x = 0.00, 0.01, 0.02, 0.03 respectively. Electrical properties including the carrier concentration, Hall mobility, and resistivity were studied using Van-der Pauw method. The temperature resistivity curves of the samples shown typical semiconductor behavior. The carrier concentration decreases with increasing doping level up to 2% Mg, and it slightly increases for 3% Mg. The variation of the Hall mobility for the samples is inversely proportional to the carrier concentration.