Catalytic behavior of YBa2Cu3O7-x in the partial oxidation of ethanol to acetaldehyde

The partial oxidation of ethanol to acetaldehyde was performed over YBa₂Cu₃O_7-x in a flow reactor. The catalytic characteristics of YB₂Cu₃O_7-x were compared with those of an individual oxide comprising the YBa₂Cu₃O_7-x . The structural change of YBa₂Cu₃O_7-x and the other catalysts after the reaction was measured by means of XRD and XPS, and it was found that the high oxidation state of copper in YBa₂Cu₃O_7-x was responsible for the higher activity and the higher selectivity for acetaldehyde.     

Characteristics of Y1Ba2Cu3O7-x high-T c superconductor prepared by partial melting process

The superconducting Y₁Ba₂Cu₃O_7-x (123) and the Y₂Ba₁Cu₁O₅(211) powders in this study were prepared by pyrophoric synthesis method with Y₂O₃ (99.9 %), BaCO₃ (99.9 %), and CuO (99.9 %) powders. Samples of 123 and 211 pellets were first prepared and then piled to have a 123/211/123 arrangement before a partial melting process was applied for phase change of the center piece (211) to 123 phase through a peritectic reaction. The process parameters were a melting temperature of 1,040–1,070 °C and the mass of the 123 piece ranging from 0.4 to 1.2 g. The superconductivity, such as critical temperature (T_c), and mass susceptibility(χ) of bulk 123 and 211 samples were measured by AC four point probe method and AC susceptometer, respectively. The experimental results can be summarized as follows: the best preparation condition in the range examined was a melting temperature of 1,060 °C and mass ratio [123(A)/211(B)] of 2:1 with melting time of 30 minutes to yield the T_c of 88.5 K.     

The catalytic activity of the ceramic superconductor YBa2Cu3O7 − δ

The superconductivity of the ceramic solid YBa₂Cu₃O_{7 ? δ}, prepared by heating Y₂O₃, BaCO₃ and CuO at 920°C for 22 h, was checked by the Meissner effect. Chemical analysis established the formula of the compound prepared. A thermostated aqueous suspension of the superconductor, treated with a solution of H₂O₂, produced oxygen, whose volume was measured at intervals in a gas burette. From the initial rates of the first-order reaction at different temperatures, the activation enthalpy and entropy were 16 kJ mol^?1 and ?210 J K^?1 mol^?1 respectively. The rates of gas evolution were similar to those obtained when a MnO₂ sample was used as a catalyst. Neither the superconductor nor its semiconductor phase photocatalysed the decomposition of KMnO₄ solution. Evidence of the catalysed decomposition of N₂H⁺₅ by the superconductor is presented.     

Catalytic hydrogenation of CO over the doped perovskite oxide YBa2Cu3O7-x catalysts

Perovskite oxide structured YBa₂Cu₃O₇-x(YBCO) has been first prepared by carbonate precipitation and then modified with palladium or ruthenium by impregnation on the perovskite oxide, while cobalt was co-precipitated simultaneously in the same pH range with perovskite oxide. After characterization the catalysts were used in the temperature range 300–450°C, in the pressure range 1–9 atmospheres and for H₂/CO ratios in the range 1–4 in a differential plug flow reactor for the hydrogenation of carbon monoxide to give hydrocarbons. The perovskite oxide (YBCO) 20% (w/w) and doped 2% (w/w) cobalt oxide catalyst were prepared by the wet chemical method from their nitrate solutions and oxidized at 950°C. Perovskite oxide (Dursun, G. & Winterbottom, J. M., J. Chem. Technol Biotechnol. 63 (1995) 113–16) was also doped with palladium and ruthenium metal by impregnation followed by oxidation at 250°C. The catalysts prepared were characterized by using TemperatureProgrammed Reduction (TPR) to observe the reduction temperature and also to measure total and metal surface area. The modified perovskite oxide on alumina, ruthenium- and cobalt-doped catalysts, has been shown to give a better conversion and also selectivity towards saturated hydrocarbons compared with palladium-doped catalyst. The temperature effect of these catalysts is more consistent, giving a steady increase of conversion with increasing temperature. Although increase of pressure increases the conversion, it causes very little change in product distribution. The activation energy of palladium- and ruthenium-doped, and cobalt co-precipitated catalysts for the reaction has been measured to be 55 kJ mol⁻¹, 75 kJ mol⁻¹ and 50 kJ mol⁻¹ respectively. A general rate equation of the form r=k[H₂]^m[CO]ⁿ has been observed and found to be applicable at the pressures and temperatures used for the catalytic system studied and found to be m≌1·0 for palladium-doped, m≌1·2 for ruthenium-doped and m≌0·95 for cobalt co-precipitated catalysts as n becomes zero or negligibly less than zero. The mechanism of reaction to produce hydrocarbons from syngas has been deduced from the results. It appeared that the carbon monoxide insertion mechanism has been more evident for palladium-doped catalysts whereas the carbide mechanism plays the main role for the ruthenium-doped and cobalt co-precipitated catalysts. © 1998 Society of Chemical Industry     

Kinetics of the catalysed decomposition of N2H by the ceramic superconductor YBa2Cu3O7–δ

This paper describes an extractive membrane bioreactor developed to extract and biodegrade toxic organic pollutants present in chemical industry wastewaters. The technology is applicable to wastewaters emanating in organic synthesis operations which are not treatable by conventional ‘direct’ biological treatment due to extremes of pH, high salt contents, or otherwise hostile organic compositions, and also to wastewaters that contain volatile organic compounds. A laboratory scale prototype demonstrating the technology has been operated continuously over periods of several months, using industrially produced wastewaters. No pre-conditioning or dilution of the wastewaters is necessary prior to treatment, which removes and destroys over 99% of the toxic organics present.     

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.     

Coprecipitation synthesis and sintering property of (YbxSm1-x)2Zr2O7 ceramic powders

Abstract

Abstract

(Yb_xSm_1-x)₂Zr₂O₇ (0<x<1·0) ceramic powders were synthesised with chemical coprecipitation and calcination method. Thermal decomposition behaviour of precipitates was studied by differential scanning calorimetry-thermogravimetry. The powders were characterised by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy. The synthesised powders have a particle size of about 100?nm, and exhibit to a certain extent agglomeration. The sintering behaviour of (Yb_xSm_1-x)₂Zr₂O₇ powders was studied by pressureless sintering method at 1550-1700°C for 10?h in air. The relative densities of (Yb_xSm_1-x)₂Zr₂O₇ ceramics increase with increasing sintering temperature, and reach above 95% when sintered at 1700°C for 10?h in air. Sm₂Zr₂O₇ and (Yb_0·1Sm_0·9)₂Zr₂O₇ ceramics have a pyrochlore structure; however, (Yb_xSm_1-x)₂Zr₂O₇ (0·3<x<1·0) ceramics exhibit a defective fluorite type structure.     

A thermogravimetric study of the partial oxidation of methanol for hydrogen production over a Cu/ZnO/Al2O3 catalyst

The partial oxidation of methanol for the production of hydrogen was investigated in both a fixed-bed microreactor and in a thermogravimetric analyzer (TG-FTIR) from 180 °C to 250 °C using a commercial Cu/ZnO/Al₂O₃ catalyst. In the microreactor, a hot spot in the undiluted catalyst bed of 4 K and 32 K was observed at 180 °C and 220 °C, respectively. Methanol conversion was strongly accelerated between 180 °C and 220 °C. In the TG-FTIR experiments, the reduced copper was completely oxidized to cuprite, Cu₂O, with increasing time-on-stream in the presence of oxygen and methanol (O₂/MeOH = 0.5) at 180 °C. The selectivity to formaldehyde increased in the same manner as the catalyst was oxidized to cuprite. In contrast, at 250 °C the catalyst remained completely reduced for the same O₂/MeOH ratio. Two main reaction pathways are proposed explaining the influence of the copper oxidation state on the product distribution.     

Cu插层H_2Ti_3O_7复合材料的制备与表征

文章采用剥离–重堆积法制备Cu-Ti3O7插层材料。该材料为多级介孔结构,表面积为182 m2·g–1。可见光下(300 W氙灯,加滤光片,λ≥420 nm),插层材料对MB的降解率为59.1%。插层材料的高光催化活性主要来自于层间的Cu2+有效地调节了半导体的能带结构,减小了带隙宽度,拓展了材料的光响应范围。     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cu2O/TiO2催化甲醛乙炔化反应的载体效应

以不同温度焙烧的TiO₂为载体,CuCl₂·2H₂O为铜源,NaOH为沉淀剂,L-抗坏血酸钠为还原剂,采用液相还原-沉积沉淀法制备了Cu₂O/TiO₂,借助X射线粉末衍射（XRD）、H₂程序升温还原（H₂-TPR）、N₂-物理吸附、透射电镜（TEM）、X射线光电子能谱（XPS）等手段,研究了TiO₂载体焙烧温度对Cu₂O/TiO₂甲醛乙炔化反应性能的影响。结果表明,低温焙烧得到的TiO₂载体以锐钛矿相存在,与Cu₂O物种间具有弱的相互作用,使得Cu₂O被过度还原为金属Cu,催化活性较低。随着载体焙烧温度的升高,TiO₂中出现金红石相,Cu₂O与载体间相互作用增强,Cu₂O高效转变为乙炔亚铜活性物种,使催化剂表现出最佳的催化性能。     

Al2O3-SiC系制品中添加物α-Cr2O3的行为

以电熔刚玉和SiC为基料的制品中添加适量亚微米级的绿铬(α-Cr2O3)时,烧成过程中α-Cr2O3生长到1～5 μm,并与刚玉表面接触区发生互扩散行为.SiC在氧化层中氧化并形成玻璃纤维,使氧化层的组分变为Al2O3-Cr2O3-SiO2系.所形成的高硅质液相能促进(Al2-x,Crx)O3固溶体析晶,晶体呈较大的六方柱状自形晶,长度达5～20 μm,长径比(a)为5～10.但此液相中不含Cr2O3.     

Effects of space velocity on methanol synthesis from Co2/Co/H2 over Cu/ZnO/Al2O3 catalyst

The space velocity had profound and complicated effects on methanol synthesis from CO₂/CO/H₂ over Cu/ZnO/Al₂O₃ at 523 K and 3.0MPa. At high space velocities, methanol yields as well as the rate of methanol production increased continuously with increasing CO₂ concentration in the feed. Below a certain space velocity, methanol yields and reaction rates showed a maximum at CO₂ concentration of 5–10%. Different coverages of surface reaction intermediates on copper appeared to be responsible for this phenomenon. The space velocity that gave the maximal rate of methanol production also depended on the feed composition. Higher space velocity yielded higher rates for CO₂/ H₂ and the opposite effect was observed for the CO/H₂ feed. For CO₂/CO/H₂ feed, an optimal space velocity existed for obtaining the maximal rate.     

Tailoring the efficient laser-absorption-melting behavior of Bi2O3-B2O3-ZnO-Nd2O3 glass for the OLED encapsulation

The efficient 810 nm laser energy conversion of glass frit had been proven to be the key to the long-term hermetic encapsulation of Organic Light Emitting Display (OLED). A direct laser energy conversion laser-assisted Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ sealing glass material without extra laser absorbent such as carbon black, was designed and systematically investigated. The addition of Nd₂O₃, as glass modifiers with higher cationic field strength, could be conducive to enhancing the polymerization of glass network structure, manifesting that the glass-transition temperature Tg, onset-crystallization temperature Tc and thermal stability ΔT (ΔT = Tc-Tg) increased, while thermal expansion coefficient CTE dropped to 9.72×10⁻⁶/°C and advantageously matched with the glass substrate (8±1×10⁻⁶/°C). More importantly, the absorption rate of BBZ-Nd glass was more than 50 % between 800∼810 nm owing to the 4f-4f electron transition of Nd³⁺ ions, and yet the reflectivity and transmittance of the wavelength at 800–810 nm were lower. As optimal compositions, the addition of 3.0 wt% Nd₂O₃ in Bi₂O₃-B₂O₃-ZnO-Nd₂O₃ glass frit with higher absorption coefficients (80 %) led to instantaneous bonding encapsulation between glass substrates without interfacial cracks or pores with the 808 nm wavelength of the laser at 20 W and 2.4 mm/s.     

A comparative study of the partial oxidation of methane to formaldehyde on bulk and silica supported MoO3 and V2O5 catalysts

The mechanism of the partial oxidation of methane to formaldehyde with O₂ has been investigated on bulk and differently loaded silica supported (4–7 wt%) MoO₃ and (5–50 wt%) V₂O₅ catalysts at 600–650°C in a pulse reactor connected to a quadrupole mass spectrometer. The reaction rate and product distribution in the presence and in the absence of gas-phase O₂ have been evaluated. On bare SiO₂, low and medium loaded silica supported MoO₃ and V₂O₅ catalysts the reaction proceeds via a concerted mechanism involving the activation of gas-phase oxygen on the reduced sites of the catalyst surface as proved by the direct correlation between catalytic activity and density of reduced sites evaluated in steady-state conditions, while on highly loaded catalysts as well as on bulk MoO₃ and V₂O₅ the reaction rate drops dramatically and the reaction pathway via redox mechanism becomes predominant. The results indicate that the surface mechanism is essentially more effective than the redox mechanism enabling also a higher selectivity to HCHO.     

Corrosion behavior of high-temperature superconductor YBa2Cu3-yAgyO7-x in the presence of water

Because of the presence of water vapor, YBa₂Cu₃O_7-x degrades easily in the atmosphere and thus very difficult to put it to practical use. When Cu is partially substituted with Ag, however, there is not much a decrease in the critical temperature (T_c) : T_c is 89 K compared with 91 K without substitution. Moreover, partial substitution of Ag increases density, hardness, and superconducting particle size and above all improves considerably its stability in water. In this study YBa₂Cu₃O_7-x and YBa₂Cu_3-yAg_yO_7-x as a result of a partial substitution of Ag for Cu were synthesized by pyrophoric method. We investigated their stabilities in water by XRD, SEM, and EPMA after immersing samples in distilled water for 3 hours. We can see that YBa₂Cu_2.94Ag_0.06O_7-x was the largest particle size and anticorrosion behavior.     

Dynamical Changes in Cu/ZnO/Al2O3 Catalysts

A combination of various transient and steady-state kinetic experiments was used to provide evidence for dynamical changes in a Cu/ZnO/Al₂O₃ catalyst of industrial interest. From these it can be deduced that the reversible structural alterations strongly depend on the reaction conditions as well as on the pretreatment. The pretreatment was found to induce changes in the morphology of the metallic Cu particles to some extent, and surface alloying under more severe reducing conditions.     

The Synergistic Effect of Adsorption-Photocatalysis for Removal of Organic Pollutants on Mesoporous Cu2V2O7/Cu3V2O8/g-C3N4 Heterojunction

Cu₂V₂O₇/Cu₃V₂O₈/g-C₃N₄ heterojunctions (CVCs) were prepared successfully by the reheating synthesis method. The thermal etching process increased the specific surface area. The formation of heterojunctions enhanced the visible light absorption and improved the separation efficiency of photoinduced charge carriers. Therefore, CVCs exhibited superior adsorption capacity and photocatalytic performance in comparison with pristine g-C₃N₄ (CN). CVC-2 (containing 2 wt% of Cu₂V₂O₇/Cu₃V₂O₈) possessed the best synergistic removal efficiency for removal of dyes and antibiotics, in which 96.2% of methylene blue (MB), 97.3% of rhodamine B (RhB), 83.0% of ciprofloxacin (CIP), 86.0% of tetracycline (TC) and 80.5% of oxytetracycline (OTC) were eliminated by the adsorption and photocatalysis synergistic effect under visible light irradiation. The pseudo first order rate constants of MB and RhB photocatalytic degradation on CVC-2 were 3 times and 10 times that of pristine CN. For photocatalytic degradation of CIP, TC and OTC, it was 3.6, 1.8 and 6.1 times that of CN. DRS, XPS VB and ESR results suggested that CVCs had the characteristics of a Z-scheme photocatalytic system. This study provides a reliable reference for the treatment of real wastewater by the adsorption and photocatalysis synergistic process.     

Ambient temperature oxidation of carbon monoxide using a Cu2Ag2O3 catalyst

The mixed copper–silver oxide, Cu₂Ag₂O₃, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu₂Ag₂O₃, aged for 4 h was at least as active as the hopcalite.     

填料型La2O3/Al2O3-Al催化剂的制备及其催化性能

以n水硝酸镧[La(NO3)3·n H2O]为原料,阳极氧化铝(Al2O3-Al)为载体,采用水热合成法将活性组分负载在Al2O3-Al上,制备了填料型固体碱催化精馏元件La2O3/Al2O3-Al,以丙酮缩合制备二丙酮醇为探针反应,考察了制备条件对催化剂性能的影响。采用XRD、SEM对催化剂的性能进行了表征。结果表明,活性组分La2O3均匀分散在载体Al2O3-Al表面上。当La(NO3)3·n H2O与氨水(NH3·H2O)的摩尔比为1∶8,油浴温度为160℃,油浴时间10 h,N2保护下焙烧温度为550℃,焙烧时间为2 h时,催化剂的活性最高,此时丙酮转化率为4.1%,二丙酮醇选择性98%。