Catalytic wet air oxidation of phenol over CeO2-TiO2 catalyst in the batch reactor and the packed-bed reactor

CeO2-TiO2 catalysts are prepared by coprecipitation method, and the activity and stability in the catalytic wet air oxidation (CWAO) of phenol are investigated in a batch reactor and packed-bed reactor. CeO2-TiO2 mixed oxides show the higher activity than pure CeO2 and TiO2, and CeO2-TiO2 1/1 catalyst displays the highest activity in the CWAO of phenol. In a batch reactor, COD and TOC removals are about 100% and 77% after 120 min in the CWAO of phenol over CeO2-TiO2 1/1 catalyst at reaction temperature of 150 degrees C, the total pressure of 3 MPa, phenol concentration of 1000 mg/L, and catalyst dosage of 4 g/L. In a packed-bed reactor using CeO2-TiO2 1/1 particle catalyst, over 91% COD and 80% TOC removals are obtained at the reaction temperature of 140 degrees C, the air total pressure of 3.5 MPa, the phenol concentration of 1000 mg/L for 100 h continue reaction. Leaching of metal ions of CeO2-TiO2 1/1 particle catalyst is very low during the continuous reaction. CeO2-TiO2 1/1 catalyst exhibits the excellent activity and stability in the CWAO of phenol.     

Simultaneous soot combustion and nitrogen oxides storage on potassium-promoted hydrotalcite-based CoMgAlO catalysts

A series of potassium-promoted hydrotalcite-based CoMgAlO mixed oxide catalysts used for simultaneous soot combustion and nitrogen oxides storage were prepared by impregnation method. The techniques of TG/DTA, XRD, H2-TPR and in situ DRIFTS were employed for catalyst characterization. Over the catalyst containing 7.5% or 10% K, the soot ignition temperature (Ti=260 degrees C) and total removal temperature (Tf=390 degrees C) are decreased by 180 degrees C and 273 degrees C, respectively, as compared with the uncatalyzed reaction. The results of kinetic calculation show that the presence of K-promoted catalysts decreases the activation energy of soot combustion from 207kJ/mol to about 160kJ/mol. When 400ppm NO is introduced, lower characteristic temperatures or higher reaction rate for soot oxidation is achieved. Simultaneously, relatively larger nitrogen oxides storage capacity is obtained. It is revealed by H2-TPR that the addition of K increases the amount of active Co sites and the mobility of bulk lattice oxygen due to the low melting point of K-containing compounds, the low valence of K+ and the strong interaction between K and Mg(Al). For nitrogen oxides storage, different routes via chelating bidentate nitrates, monodentate nitrates and ionic nitrates are confirmed by in situ DRIFTS over the CoMgAlO catalysts with potassium loadings of 0, 1.5 and 7.5%, respectively.     

Effect of submicron grains on ionic conductivity of nanocrystalline doped ceria

Doped ceria has been considered for high oxygen ion conductivity for solid oxide fuel cells. In the present study, 20 mole% samarium doped nano ceria powder was prepared by wet chemical synthesis and sintered at different temperatures to retain submicron grains (> 92-96% density). ionic conductivity of the sintered pellets was measured using impedance spectroscopy as a function of temperature (200-800 degrees C). The total maximum conductivity was 1.0 x 10(-2)S.cm(-1) (at 600 degrees C) for samples sintered at 1200 degrees C. The activation energy at higher test temperature decreases with the decrease in the sintering temperature (by 25%). The grain boundary, grain interior conductivity and activation energy of the electrolyte were correlated to the resulting microstructure. It has been demonstrated that use of doped nano ceria powder as precursor not only reduced the sintering temperature but also provided segregation free grain boundary for engineering higher conductivity dense electrolytes.     

THE INFLUENCE OF SYNTHESIS PARAMETERS ON THE PRODUCTION OF MULTIWALLED CARBON NANOTUBES BY THE FERROCENE CATALYZED PYROLYSIS OF TOLUENE

A high yield (∼32 wt.%) of multiwalled carbon nanotubes was obtained in an iron catalyzed reaction. This was achieved in the temperature range 800-1000°C under an atmosphere of H₂/Ar by an improved solution injection method in a horizontal reactor using toluene as carbon source and ferrocene as catalyst precursor. The pyrolysis temperature, ferrocene concentration, solution feeding rate and carrier gas flow rate all influenced the yield of carbon nanotubes and the thickness of the aligned carbon nanotube films. The carbon nanotubes was prepared in high purity using optimized pyrolysis conditions.     

化学镀制备高温质子导体镍电极及其电化学性能

采用化学镀在高温质子导体CaZr_0.9In_0.1O_3-δ (CZI)的电解质陶瓷表面沉积金属镍电极, 通过SEM显微结构分析比较了酸刻蚀和还原工艺对电极形貌以及电极-电解质界面的影响。结果表明, 使用HNO₃-HCl混合刻蚀液, 并以水合肼为还原剂的二次化学镀可获得颗粒均匀细小且界面结合良好的镍电极。通过电化学阻抗谱并结合浓差电池等方法研究比较了以化学镀镍电极和涂覆焙烧铂电极为电极, CZI为电解质的对称电池的电导率和质子迁移率。工作温度为800℃时, 镍电极高温质子导体的总电导率为4.131×10^-4 S/cm, 并且工作温度在400℃以上时, 镍电极对称电池的质子迁移率均接近100%。这些结果表明, 二次化学镀制备的镍电极具有与铂电极相近的电化学性能, 而成本则更低, 可以取代Pt电极用于高温质子导体的电化学器件中。     

Study of Ln0.6Sr0.4Co0.8Mn0.2O3-δ (Ln=La, Gd, Sm or Nd) as the cathode materials for intermediate temperature SOFC

Perovskite type oxides Ln_0.6Sr_0.4Co_0.8Mn_0.2O_3−δ (Ln=La, Gd, Sm, or Nd) have been prepared by the solid state reaction of corresponding oxides. The crystal parameters of the compositions were determined by XRD powder diffraction, which revealed that all the compositions have orthorhombic structure. The reaction test of all samples with Ce_0.8Gd_0.2O_1.9 was carried out at 1200 °C for 48 h, and no reaction product was detected by XRD. The change in mass of La_0.6Sr_0.4Co_0.8Mn_0.2O_3−δ as a function of temperature was determined by thermogravimetric analysis (TGA). The electrical conductivity of the sintered samples were measured as a function of temperature from 200 to 1000 °C. The highest conductivity of about 1400 S cm⁻¹ was found in La_0.6Sr_0.4Co_0.8Mn_0.2O_3−δ. The cathodic polarization of these oxides electrodes deposited on Ce_0.8Gd_0.2O_1.9 tablet was studied at 500-800 °C in air.     

Influence of Lithium Oxide Addition on the Sintering Behavior and Electrical Conductivity of Gadolinia Doped Ceria

Ceria-based electrolytes have been widely researched in intermediate-temperature solid oxide fuel cell (SOFC), which might be operated at 500-600?C. Sintering behavior with lithium oxide as sintering additive and electrical conductivity of gadolinia doped ceria (Gd0.1Ce0.9O2δ, GDC10) electrolyte was studied in this paper by X-ray di?raction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). As the results, the fully dense GDC10 electrolytes are obtained at a low temperature of 800?C with 2.5 mol% Li2O as sintering additive (called 5LiGDC800). During sintering process, lithium oxides adsorbed by around GDC10 surface help to sinter at 800?C and are kept at the grain boundary of GDC10 in the end. The fine grains of 100-400 nm and high electrical conductivity of 0.014 S/cm at 6000C in 5LiGDC800 were achieved, which contributed to the lower sintering temperature and enhanced grain boundary conductivity, respectively. Lithium, staying at grain boundary, reduces the depletion of oxygen vacancies in the space charge layers and increases the oxygen vacancy concentration in the grain boundary, which leads to improve the total electrical conductivity of 5LiGDC800.     

Bimetallic Ni–Mo nitride@C3N4 for highly active and stable water catalysis

Non-noble metal electrocatalysts for water cracking have excellent prospects for development of sustainable and clean energy. Highly efficient electrocatalysts for the oxygen evolution reaction (OER) are very important for various energy storage and conversion systems such as water splitting devices and metal‒air batteries. This study prepared a NiMo₄@C₃N₄ catalyst for OER and hydrogen evolution reaction (HER) by simple methods. The catalyst exhibited an excellent OER activity based on the response at a suitable temperature. To drive a current density of 10 mA·cm⁻² for OER and HER, the overpotentials required for NiMo₄@C₃N₄-800 (prepared at 800 °C) were 259 and 118 mV, respectively. A two-electrode system using NiMo₄@C₃N₄-800 needed a very low cell potential of 1.572 V to reach a current density of 10 mA·cm⁻². In addition, this catalyst showed excellent durability after long-term tests. It was seen to have good catalytic activity and broad application prospects.     

Design of low cost gas sensor based on SrTiO3 and BaTiO3 films

We have prepared SrTiO3/BaTiO3 multilayer film on alumina substrates by a sol-gel technique and investigated their response for sensing ethanol vapor. The surface morphology of the films were characterized by atomic force microscope (AFM) showing that the grain size of the films increase up to 40 nm as the annealing temperature increased to 1000 degrees C. The ethanol sensors based on SrTiO3/BaTiO3 thin films were fabricated by applying interdigitated gold electrodes by sputtering technique. The ethanol sensing characteristics of SrTiO3/BaTiO3 thin films were quantified by the change in resistance of the sensors when they were exposed to ethanol. The optimum operating tempearature of these sensors was found to be 350 degrees C. In addition, the film annealed at 1000 degrees C exhibited p-type gas sensing behavior with the best sensitivity of 30-100 for low ethanol concentration in the range of 100-1000 ppm.     

Hierarchical N-Doped Porous Carbons for Zn–Air Batteries and Supercapacitors

Nitrogen-doped carbon materials with a large specific surface area,high conductivity,and adjustable microstructures have many prospects for energy-related applications.This is especially true for N-doped nanocarbons used in the electrocatalytic oxygen reduction reaction(ORR)and supercapacitors.Here,we report a low-cost,environmentally friendly,large-scale mechanochemical method of preparing N-doped porous carbons(NPCs)with hierarchical micro-mesopores and a large surface area via ball-milling polymerization followed by pyrolysis.The optimized NPC prepared at 1000°C(NPC-1000)offers excellent ORR activity with an onset potential(Eonset)and half-wave potential(E1/2)of 0.9 and 0.82 V,respectively(vs.a reversible hydrogen electrode),which are only approximately 30 mV lower than that of Pt/C.The rechargeable Zn–air battery assembled using NPC-1000 and the NiFe-layered double hydroxide as bifunctional ORR and oxygen evolution reaction electrodes offered superior cycling stability and comparable discharge performance to RuO2 and Pt/C.Moreover,the supercapacitor electrode equipped with NPC prepared at 800℃ exhibited a high specific capacity(431 F g^−1 at 10 mV s^−1),outstanding rate,performance,and excellent cycling stability in an aqueous 6-M KOH solution.This work demonstrates the potential of the mechanochemical preparation method of porous carbons,which are important for energy conversion and storage.     

Characterizations of tungsten carbide as a non-Pt counter electrode in dye-sensitized solar cells

Tungsten carbide particles as a counter electrode for dye-sensitized solar cells are prepared by heating layered tungsten oxides at 700, 800, and 900 °C. In particular, the sample heated at 800 °C reveals dominant WC structure and relatively high specific surface area. The improved photoelectrochemical properties of the sample prepared at 800 °C may be due to both catalytic activity of WC phase and high active sites for iodide reduction in comparison with other electrodes.     

Growth of zinc oxide nanorods, tetrapods, and nanobelts without catalyst

Zinc oxide (ZnO) nanostructures with various morphologies have been synthesized without catalyst in a one-step simple redox process. The results show that ZnO nanorods, nanobelts, and tetrapods with hexagonal needled arms could be synthesized via thermal treatment of a mixture of zinc oxide and charcoal powder in a muffle furnace at 1000-1200 degrees C for 240 min. XRD analyses showed that polycrystalline ZnO phase with wurtzite crystal structure was formed. At a relatively low temperature, 1000 degrees C, the ZnO structure was found to be a bundle of denser nanorods. By increasing the reaction temperature to 1100 degrees C, tetrapod-like structures of needle-like arms with pyramidal tips were formed. With the increase of temperature up to 1200 degrees C, the morphology of ZnO nanostructures changed from nanorods and tetrapods to coalescence grains. Reaction temperature was found to be the most important experimental parameter that played an important role in controlling the mode, mechanism of growth, and formation of different ZnO morphologies.     

MnOx-CeO2-Al2O3 mixed oxides for soot oxidation: activity and thermal stability

MnO(x)-CeO(2)-Al(2)O(3) mixed oxides were prepared by impregnating manganese acetate and cerium nitrate on alumina powders using the sol-gel method. The thermal stabilities of MnO(x)-CeO(2) and Al(2)O(3)-modified mixed oxides were evaluated by treating at 800 °C in dry air flow for 20h. The introduction of Al(2)O(3) markedly increases the textural stability of the catalyst with a relatively high dispersion of MnO(x) and CeO(2), remaining a strong synergistic effect between these two oxides. The NO oxidation activity of the ternary oxides experiences a smaller loss after high-temperature calcination, and a low soot oxidation temperature is attained in the presence of NO.     

Synthesis of yttria-doped bismuth oxide powder by carbonate coprecipitation for IT-SOFC electrolyte

Yttria-doped bismuth oxide (YBO) powders were synthesized by ammonium carbonate coprecipitation for the preparation of electrolytes of an intermediate temperature solid oxide fuel cell (IT-SOFC). The starting salts were yttrium and bismuth nitrate. The crystal structures and the morphological characteristics of the particles were analyzed by XRD and SEM, respectively. The ionic conductivity of the sintered pellet was measured by an electrochemical impedance analyzer. The size of the calcined YBO powders were in the range of 20-100 nm as measured by SEM images. The YBO pellets had a face-centered cubic structure, and their crystallite size was about 54-88 nm. The ionic conductivity of the YBO pellets sintered at 800 degrees C was observed to be 2.7 x 10(-1) Scm-(-1) at 700 degrees C. The ball-milling of the YBO powder before it was pelletized was found to have been unrequired probably because of a good sinterability of the YBO powders that was prepared via the ammonium carbonate coprecipitation method. The results showed that the ammonium carbonate coprecipitation process could be used as the cost-efficient method of producing YBO electrolytes for IT-SOFC.     

Mechanical strength and electrical conductivity of Ni-YSZ cermets fabricated by viscous processing

A method for manufacturing of profiled Ni-YSZ anode support sheets by water-based viscous processing has been developed. Mechanical and electrical properties have been studied and were found to correlate with the microstructures and heat treatment. Electrical conductivities in the order of 1000 S/cm were obtained at 1000°C. The results reveal a linear dependence between the conductivity and pre-test reduction temperature: the conductivity increases by a factor of about 6 when reducing the anode support at 1000°C compared to 650°C. Heat treatment after the reduction at low temperature does not improve the conductivity. Insignificant degradation with time was observed at test temperatures between 800 and 1000°C. However, very high electrical loads did lower the conductivity. The developed microstructure withstood two redox cycles without decrease in conductivity. The mechanical strength of components, optimised with respect to both conductivity and strength, showed little change in strength upon reduction, i.e. when changing the structure from NiO/YSZ to Ni/YSZ, revealing that the YSZ matrix governs the mechanical strength.     

Uptake properties of Ni2+ by nCaO.Al2O3.2SiO2 (n=1-4) prepared from solid-state reaction of kaolinite and calcite

A series of nCaO.Al2O3.2SiO2 samples (n=1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 degrees C for 24 h. All the samples were X-ray amorphous after firing at 600-800 degrees C but had crystallized by 900 degrees C. The main crystalline phases were anorthite (n=1), gehlenite (n=2 and 3) and larnite (n=4). The uptake of Ni2+ by nCaO.Al2O3.2SiO2 samples fired at 800 and 900 degrees C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 degrees C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 degrees C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO.Al2O3.2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.     

Preparation and sintering properties in air of silver-coated copper powders and pastes

In this paper, uniform and well dispersed silver-coated copper powders were prepared by replacing reaction at first. The structure and properties of the bimetallic powders were investigated by XRD, SEM and TGA. It was found that anti-oxidization of the silver-coated copper powders increased with the increase of the silver content slightly and a dense coating surface was observed at Ag content of 53.9 wt%. Furthermore, the pastes with relatively low silver content which were prepared from silver-coated copper powders, displayed high conductivity similar to pure silver even after sintering in air. And their sintering properties were also investigated at different temperature in air atmosphere. The film exhibits good electrical properties at sintering temperature between 800 and 900 °C. When the paste from silver-coated copper powder with Ag content of 53.9 wt% was printed on Al₂O₃ substrate and sintered at 800 °C in air, the sheet resistance of the film is 0.036 Ω/□ only.     

Nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition

Nano-polycrystalline vanadium oxide thin films have been successfully produced by pulsed laser deposition on Si(100) substrates using a pure vanadium target in an oxygen atmosphere. The vanadium oxide thin film is amorphous when deposited at relatively low substrate temperature (500 degrees C) and enhancing substrate temperature (600-800 degrees C) appears to be efficient in crystallizing VOx thin films. Nano-polycrystalline V3O7 thin film has been achieved when deposited at oxygen pressure of 8 Pa and substrate temperature of 600 degrees C. Nano-polycrystalline VO2 thin films with a preferred (011) orientation have been obtained when deposited at oxygen pressure of 0.8 Pa and substrate temperatures of 600-800 degrees C. The vanadium oxide thin films deposited at high oxygen pressure (8 Pa) reveal a mix-valence of V5+ and V4+, while the VOx thin films deposited at low oxygen pressure (0.8 Pa) display a valence of V4+. The nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition have smooth surface with high qualities of mean crystallite size ranging from 30 to 230 nm and Ra ranging from 1.5 to 22.2 nm. Relative low substrate temperature and oxygen pressure are benifit to aquire nano-polycrystalline VOx thin films with small grain size and low surface roughness.     

Some properties of thin layers of silica containing carbon and iron oxides prepared by the sol-gel method

Thin layers of silica containing carbon and iron oxides have been prepared by the sol-gel method. The samples were investigated using Auger electron spectroscopy, energy loss, microhardness and Mössbauer effect measurements. It is shown that carbon is located in the pores of the silica network. The electrical conductivity depends on the temperature of heat treatment in the vacuum. The maximum value of conductivity was observed for an annealing temperature about 600 to 800° C. All samples exhibited low activation energy 0.12 eV. It is suggested that the mechanism of conductivity can be interpreted as a tunnelling process of electrons between carbon granules.     

Fabrication and characterization of solid oxide fuel cell electrolyte films by electron beam vapor deposition

Thin films of SDC for SOFC electrolyte were prepared using electron beam deposition technique. The influence of annealing temperature, substrate temperature and e-beam gun power on the structure and surface morphology of the thin films was examined. It was found that the SDC thin films annealed at 800 degrees C consisted of a single cubic phase and the main crystal structure of the thin films represented those of evaporated electrolyte powders. The crystal orientation of the SDC films increased with substrate temperature and decreased with e-beam gun power. The higher XRD peak intensity was observed for the SDC films deposited on NiO-YSZ substrate compared with those on SiO2 substrate due to the polycrystalline structure of the NiO-YSZ substrate. A good adhesion to the substrate and a columnar structure were observed by the fractured cross-sectional view of the SDC films on NiO-YSZ anode substrate. Electrical conductivity of SDC film with 5 microm thickness was observed to be 2.31 x 10(-3) Sm(-1) at 800 degrees C.