Cu/SiO2催化剂在醋酸甲酯加氢制乙醇反应中失活比较

采用固定床微型反应器考察Cu/ZnO和Cu/SiO₂催化剂在醋酸甲酯加氢制乙醇反应中的稳定性,分别反应1 000 h和750 h后,Cu/ZnO和Cu/SiO2催化剂均失活。采用物理吸附、DTG、原位XRD和H₂-TPR等对失活前后Cu/ZnO和Cu/SiO₂催化剂进行比较。结果表明,Cu/ZnO和Cu/SiO₂催化剂在醋酸甲酯加氢制乙醇反应中失活机理不同,Cu/ZnO 催化剂失活的主要原因是Cu晶粒长大,催化剂上ZnO晶粒同时长大;Cu/SiO₂催化剂失活主要原因是积炭物种对催化剂孔道的堵塞和对活性位的覆盖。     

Methanol synthesis over Cu/SiO2 catalysts

The rates of CO and CO/CO₂ hydrogenation at 4.2 MPa and 523 K are reported for a series of Cu/SiO₂ catalysts containing 2 to 88 wt.% Cu. These catalysts were prepared on a variety of silica sources using several different Cu deposition techniques. In CO/CO₂ hydrogenation, the rate of methanol formation is proportional to the exposed Cu surface area of the reduced catalyst precursor, as determined by N₂O frontal chromatography. The observed rate, 4.2×10^–3 mole CH₃OH/Cu site-sec, is within a factor of three of the rates reported by others over Cu/ZnO and Cu/ZnO/Al₂O₃ catalysts under comparable conditions. These results suggest that the ZnO component is only a moderate promoter in methanol synthesis. Hydrogenation of CO over these catalysts also gives methanol with high selectivity, but the synthesis rate is not proportional to the Cu surface area. This implies that another type of site, either alone or in cooperation with Cu, is involved in the synthesis of methanol from CO.     

Cu2O/Cu/SiO2纳米复合物的制备及光催化性质研究

采用正硅酸乙酯和硫酸铜为原料,通过Sol-gel法制备了Cu2O/Cu/SiO2纳米复合物。研究了反应中各种因素对产物的影响,确定了最佳反应条件。利用SEM、XRD、EDX、UV-vis、FT-IR、PL等对产物进行了表征。光催化分解有机物实验证明所得产物具有较好的光催化活性。     

Thermal expansion behavior of Cu/Cu2O cermets with different Cu structures

Cu/Cu₂O cermets were prepared with Cu₂O matrix imbedded with branch-like or spherical Cu powders. The coefficients of thermal expansion (CTE) of them were tested. The CTE curves can be divided into three segments. From 25 °C to 150 °C, CTEs were found to decrease with temperatures. The CTEs were influenced by the structure of the conductor phase. For cermets prepared with spherical Cu, the increase in CTEs was basically linear with temperatures above 150 °C. In contrast, cermets with same Cu content prepared with branch-like Cu had a CTE with an increasing rate as the temperature rose from 150 °C to 900 °C, and the increasing rates in these temperature range are much higher than those prepared with spherical Cu.     

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.     

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce_1-xCu_xO_2- mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce_1-xCu_xO_2- mixed oxides indicated that Cu²⁺ ions were dissolved in CeO₂ lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO₂ promotes the reduction of the Cu²⁺ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu²⁺ species in the Ce_1-xCu_xO_2- mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu²⁺ species which dissolved into the CeO₂ lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO₂. The Ce_1-xCu_xO_2- mixed oxides were reduced to form Cu/CeO₂ catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL₂O₃ catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO₂ (over 97%) and H₂. A 3.8wt% Cu/CeO₂ catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol^-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL₂O₃ (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO₂ catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO₂ support. Slow deactivations were observed over the 3.8wt% Cu/CeO₂ catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H₂ at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO₂ catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.     

多孔碳负载Cu2O/Cu双相催化剂的制备及其在对硝基苯酚还原中的应用

采用溶剂热合成和气氛焙烧后处理方法制备了多孔碳负载的Cu2O/Cu双相纳米晶,并系统探究了该催化剂在对硝基苯酚催化还原中的催化活性。XRD表征表明在空气中焙烧金属有机框架材料Cu-BTC可以得到CuO纳米材料,而在氮气气氛中焙烧Cu-BTC则可以得到多孔碳负载的Cu2O/Cu双相纳米晶材料。论文通过扫描电镜和透射电镜对比了不同条件下制备的铜基催化剂的微观形貌,相对于空气气氛中制备的CuO催化剂,氮气气氛中制备的Cu2O/Cu双相催化剂具有更小的粒径、分散度和高比表面积。对硝基苯酚催化还原实验结果表明, 相对于空气气氛中制备的CuO催化剂,氮气气氛中制备的Cu2O/Cu双相催化剂在对硝基苯酚的还原中具有更高的催化活性。     

Influence of embedding Cu nano-particles into a Cu/SiO2/Pt structure on its resistive switching

Cu nano-particles (Cu-NPs) were embedded into the SiO₂ layer of a Cu/SiO₂/Pt structure to examine their influence on resistive switching characteristics. The device showed a reversible resistive switching behavior, which was due to the formation and rupture of a Cu-conducting filament with an electrochemical reaction. The Cu-NPs enhanced the local electric field within the SiO₂ layer, which caused a decrease in the forming voltage. During successive switching processes, the Cu-NP was partially dissolved, which changed its shape. Therefore, the switching voltages were not reduced. Moreover, the Cu-NPs caused a non-uniform Cu concentration within the SiO₂ layer; thus, the Cu-conducting filament should be formed in a high Cu concentration region, which improves switching dispersion. The Cu-NPs within the SiO₂ layer stabilize the resistive switching, resulting in a larger switching window and better endurance characteristics.     

Binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] nanocomposites: formation, characterization and catalytic performance in partial ethanol oxidation

Cuprous oxide agglomerates composed of 4-10 nm Cu2O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O2CCCH3NOMe](2)·2H2O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu2O. The precursor decomposes either in air or under argon to yield CuO2 by in situ redox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu2O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4-10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu2O/ZnO/MWCNT] clearly reveal that Cu2O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu2O/MWCNT] and [Cu2O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu2O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu2O/ZnO/MWCNT] composite shows preferential hydrogen and CO2 formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.     

氧化亚铜-活性炭复合光催化材料的制备与表征

以硫酸铜、亚硫酸钠为原料、明胶为分散剂,以活性炭为载体,采用原位合成法制备氧化亚铜一活性炭复合光催化剂。为了研究活性炭对复合光催化材料的影响,表征了复合光催化剂的相结构,光谱特征和表面形貌。测试结果显示活性炭的存在影响了氧化亚铜的相结构,但并没有影响氧化亚铜的能阀结构。在可见光条件下,对苯酚的光催化测试结果显示,氧化亚铜一活性炭复合光催化剂的光催化活性要高于氧化亚铜的光催化活性。     

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.     

A new method of low-temperature methanol synthesis on Cu/ZnO/Al2O3 catalysts from CO/CO2/H2

A new synthesis method of low-temperature methanol proceeded on Cu/ZnO/Al₂O₃ catalysts from CO/CO₂/H₂ using 2-butanol as promoters. The Cu/ZnO/Al₂O₃ catalysts were prepared by co-impregnation of r-Al₂O₃ with an aqueous solution of copper nitrate and zinc nitrate. The total carbon turnover frequency (TOF), the yield and selectivity of methanol were the highest by using the Cu/ZnO/Al₂O₃ catalyst with copper loading of 5% and the Zn/Cu molar ratio of 1/1, which precursor were not calcined, and reduced at 493 K. The activity of the catalysts increased due to the presence of the CuO/ZnO phase in the oxidized form of impregnation Cu/ZnO/Al₂O₃ catalysts. The active sites of the Cu/ZnO/Al₂O₃ catalyst for methanol synthesis are not only metallic Cu but also special sites such as the Cu–Zn site, i.e. metallic Cu and the Cu–Zn site work cooperatively to catalyze the methanol synthesis reaction.     

Electro-reduction of Cu2O to Cu in urea/1-ethyl-3-methylimidazolium chloride

Journal of Applied Electrochemistry - Urea/1-ethyl-3-methylimidazolium chloride (urea-EMIC) was developed to electrodeposit Cu from Cu2O at room temperature. Density, viscosity and conductivity of...     

Ablation-Resistance of Combustion Synthesized TiB2–Cu Cermet

TiB₂–Cu ceramic–metal composites were prepared by combustion synthesis of elemental titanium, boron, and copper powders. The synthesized product consisted of two phases: TiB₂ and copper. The addition of copper improved the strength and fracture toughness, thermal expansion coefficient, and thermal conductivity of TiB₂. Thermal shock and ablation resistances of TiB₂–Cu composites were studied using a plasma torch arc heater. Monolithic TiB₂ failed catastrophically when the plasma arc flow reached the specimen surface. However, no cracks were found on the ablation surface of the TiB₂–Cu ceramic–metal composites. The fractional mass loss was 4.09% for a TiB₂–40Cu composite, which was close to the traditional W/Cu alloys. Volatilization of metal binder and mechanical erosion of TiB₂ were observed to be the major ablation mechanisms. An ablation process model is proposed for the TiB₂–Cu composites.     

The surface condition effect of Cu2O flower/grass-like nanoarchitectures grown on Cu foil and Cu film

Cu₂O flower/grass-like nanoarchitectures (FGLNAs) were fabricated directly on two category specimens of Cu foils and Cu film using thermal oxidation method. The FGLNAs are approximately 3.5 to 12 μm in size, and their petals are approximately 50 to 950 nm in width. The high compressive stress caused by a large oxide volume in the Cu₂O layer on the specimen surface played an important role in the growth of FGLNAs. The effects of surface conditions, such as the surface stresses, grain size, and surface roughness of Cu foil and Cu film specimens, on the FGLNA growth were discussed in detail.

PACS

81. Materials science; 81.07.-b Nanoscale materials and structures: fabrication and characterization; 81.16.Hc Catalytic methods     

Effect of Cu powder addition on thermoelectric properties of Cu/TiO2−x composites

Spark plasma sintering was used to fabricate Cu/TiO_2−x composites by adding Cu powder to nonstoichiometric titanium dioxide, TiO_2−x. The composition and crystal forms of the composites were examined. The thermoelectric properties of the composites were measured and the effects of composite formation on these properties were discussed. The rule of mixture (ROM) of composite and general effective medium theory (GEM) were used to investigate the composite effects of the Cu/TiO_2−x composites. The results revealed that the electrical resistivities of the composites was much lower than that of TiO_2−x. As the added amount of Cu powder increased, the electrical properties of the composites shifted from semiconductor behavior to metallic behavior. The thermoelectric performances of the composites improved as a result of composition formation. The thermoelectric performance can be improved by adjusting the balance among electrical resistivity, thermal conductivity and the Seebeck coefficient, based on the composite effects.     

Experimental Study on Photocatalytic Activity of Cu2O/Cu Nanocomposites Under Visible Light

Cu₂O/Cu nanocomposites (NCs) are synthesized using a two-step hydrothermal method, their different phase compositions are obtained by adjusting the reaction time, and then, they are used as photocatalysts to degrade dye Procion Red MX-5B (PR), methylene blue (MB) and methyl orange (MO) under visible-light. Experimental results indicate Cu₂O/Cu NCs exhibit a much higher photocatalytic activity than pure Cu₂O, they remain almost unchanged in their phase compositions in the long photocatalytic reaction process, except for partial oxidation of particle surface. They still exhibit a high photocatalytic activity even at the end of four photocatalytic reaction cycles. It can therefore be concluded that Cu₂O/Cu nanocomposites are good candidates for processing of pollutant water.     

Simple microwave synthesis of TiO2/NiS2 nanocomposite and TiO2/NiS2/Cu nanocomposite as an efficient visible driven photocatalyst

Approximately 47% of solar-terrestrial radiation is visible. It is a great achievement to produce a highly efficient visible driven photocatalyst. Here TiO₂/NiS₂/Cu nanocomposite was prepared as a highly active visible driven photocatalyst. TiO₂/NiS₂/Cu nanocomposite was prepared by microwave method. It degrades 92%, 86%, 87%, and 88% of Rhodamine B (RhB), Methyl orange (MO), Acid Black 1 (AB1), and Acid Brown 214 (AB214), respectively. Adding NiS₂ and Cu to TiO₂ dramatically increased the degradation efficiency from 17% for bare TiO₂ to 92% for TiO₂/NiS₂/Cu nanocomposite under visible light. As-prepared TiO₂/NiS₂/Cu nanocomposite was characterized by SEM, TEM, XRD, DRS, BET, and EDX.     

Catalytic behaviour of Cu/ZrO2 and Cu/ZrO2(SO 4 2− ) in the reduction of nitric oxide by decane in oxygen-rich atmosphere

The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO₂ and Cu/ZrO₂(SO ₄ ^2– ). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO₂ is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO₂ between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO₂(SO ₄ ^2– ). About 40% NO conversion to N₂ is observed with GHSV of 70 000 h^–1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H₂.     

Cu/SiO2催化剂载体预处理工艺的研究

对硝基苯加氢制苯胺Cu/SiO₂催化剂载体的预处理工艺进行研究,考察预处理工艺条件对硅胶孔结构的影响。对经过预处理和未经过预处理的载体制备的催化剂活性进行对比测试,结果表明,预处理载体制备的催化剂,保持高转化率的时间较未经预处理载体制备的催化剂保持高活性的时间长,说明载体经过预处理制备的催化剂达到了延长使用寿命的效果。