Reaction of YBa2Cu3O7-δ Powder with NOx Gas in an Aerosol Reactor

Thermodynamic calculations predict, and experiments verify, that YBa₂Cu₃O₇-₈ (123) powder is unstable in the presence of NO_x-containing aerosol reactor exhaust gases at temperatures below about 600°C. Powders collected above the stability temperature are single-phase 123, while powders collected at lower temperature contain Ba(NO₃)₂ formed by reaction of the powder with NO_x, after exit from the hot zone.     

限碳背景下燃煤电厂对策分析与电化学催化还原技术进展

分析了目前CO₂减排的压力和趋势,以电化学催化还原为技术核心,结合燃煤排放特点,对电化学体系进行了优选,提出限碳背景下燃煤电厂的减排策略。在缓解日益严峻的CO₂减排和温室效应问题的同时,将大体量废弃的CO₂转化为具有利用价值的产品是碳捕集与利用的必由之路。对CO₂电化学催化还原技术的过程原理进行简要阐述,围绕电极、电解质、CO₂溶解性、反应器形式进行讨论,结合电化学催化还原技术特点和燃煤电厂结构特征,对大体量、低浓度CO₂电化学催化还原条件进行筛选,确定了以Cu基气体扩散电极-离子液体-连续式反应器为核心的基本电化学体系,进而提出燃煤电厂烟气中CO₂电化学催化还原对策,但在向实际应用转化过程中该技术仍面临非理想气源中杂质的影响、还原电流密度低引发的产物生成速率慢、电极寿命短、产物多样性伴随的分离及提纯难度大等障碍,为面向应用的技术发展指明了研究方向。     

Optimization of a Composite Working Electrode for a New Family of Electrochemical Cell for NO Decomposition

The electrochemical properties of a composite (NiO) _x −(yttria-stabilized zirconia (YSZ))_{1– x} working electrode for a new type of electrochemical cell for NO decomposition in the presence of excess oxygen are investigated. It is shown that the dependence of the NO conversion on the value of the current passed through the electrochemical cell with a nanoporous (NiO) _x −(YSZ)_{1– x} working electrode is linear and that the value of current efficiency depends on the NO and O₂ gas concentrations only (η= [NO] /([NO] + 2[O₂]). The optimum NiO addition (35% by volume) to the YSZ resulted in a decrease of the cell operating voltage and, as a result, in a decrease in the electrical power required for NO decomposition. The observed high performance of the composite working electrode at this composition is consistent with the effective medium percolation theory, which predicts the ambipolar transport behavior of the composite mixed ionic−electronic (YSZ–NiO) conductors as a function of the volume fraction of each of the randomly distributed constituent phases.     

Formation of Silicalite-1 in Channels of Novel SiO2–ZrO2 Porous Glass Tubes Used as Both a Silica Source and a Substrate

Silicalite-1 has been prepared using a novel SiO₂–ZrO₂ porous glass tube as both a silica source and a substrate. The SiO₂–ZrO₂ glass tube was found to possess sufficient physical strength to enable practical use as a separation and catalytic membrane after silicate-1 deposition within its channel. This is in contrast to porous SiO₂ glass which cannot be used to synthesize a silicalite-1 deposited membrane with enough physical strength to perform gas permeance measurements.     

Improvement of NO2 a Sensing Performances by an Additional Second Component to the Nano-Structured NiO Sensing Electrode of a YSZ-Based Mixed-Potential-Type Sensor

Nano-sized NiO powder was modified by the addition of BaO, La₂O₃, and CuO (10 wt% each) to change its morphology and electrochemical catalytic activities. Then, the NO _x -sensing characteristics of mixed-potential-type YSZ-based planar sensor attached with each of the obtained NiO-based samples as a sensing electrode (SE) were examined at elevated temperatures. As a result, the CuO-added NiO SE was found to give a large enhancement in the NO₂ sensitivity as well as the NO₂ selectivity at 800°C even under a wet condition, in comparison with the pure NiO SE.     

Electrocatalytic reforming of carbon dioxide by methane in SOFC system

The reaction of carbon dioxide catalytic reforming with methane is an attractive route because these greenhouse gases can be converted into variable feedstocks. However this reaction is a highly energy consuming and coke forming process. These problems were improved by the electrocatalytic reforming of CO₂ with CH₄ in a solid oxide fuel cell (SOFC) membrane reactor system, which generates high electrical power and synthesis gases. The single cell consists of catalyst electrode (NiO–MgO), counter electrode ((La,Sr)MnO₃) and Y₂O₃ stabilized ZrO₂ (YSZ) electrolyte. The reaction rates of CO₂ and CH₄, and the electrochemical properties were investigated by an on-line GC and impedance-analyzer under open- and closed-circuit conditions, respectively. It was found that reaction rates of CO₂ and CH₄ under the closed-circuit condition were more stable than those of the open-circuit. The results were interpreted that the stability of catalyst anode was maintained by the reaction of oxygen ion transferred from the cathode with the surface carbon formed in the internal CO₂ reforming by CH₄ in SOFC system.     

Electrochemical analysis and convection-enhanced mass transfer synergistic effect of MnOx/Ti membrane electrode for alcohol oxidation

The different electrocatalytic reactors could be constructed for the electrocatalytic oxidation of 2,2,3,3-tetrafluoro-1-propanol(TFP) with two typical MnO_x/Ti electrodes, i.e.the electrocatalytic membrane reactor(ECMR) with the Ti membrane electrode and the electrocatalytic reactor(ECR) with the traditional Ti plate electrode.For the electro-oxidation of TFP, the conversion with membrane electrode(70.1%) in the ECMR was 3.3 and 1.7 times higher than that of the membrane electrode without permeate flow(40.8%) in the ECMR and the plate electrode(21.5%) in the ECR, respectively.Obviously, the pore structure of membrane and convection-enhanced mass transfer in the ECMR dramatically improved the catalytic activity towards the electro-oxidation of TFP.The specific surface area of porous electrode was 2.22 m~2·g~(-1).The surface area of plate electrode was 2.26 cm~2(1.13 cm~2× 2).In addition, the electrochemical results showed that the mass diffusion coefficient of the MnO_x/Ti membrane electrode(1.80 × 10~(-6) cm~2·s~(-1)) could be increased to 6.87 × 10~(-6) cm~2·s~(-1) at the certain flow rate with pump, confirming the lower resistance of mass transfer due to the convection-enhanced mass transfer during the operation of the ECMR.Hence, the porous structure and convection-enhanced mass transfer would improve the electrochemical property of the membrane electrode and the catalytic performance of the ECMR,which could give guideline for the design and application of the porous electrode and electrochemical reactor.     

Electrochemical Determination of the Activity of Na2O in the Pyrochlore Phase of the Sb2O4-NaSbO3 System

Activity of Na₂O in the pyrochlore phase of the system Sb₂O₄-NaSbO₃ has been measured as a function of temperature in the range 1073–1412 K by electromotive force (emf) measurements of the following solid-state electrochemical cells:
The solid electrolyte used in the above electrochemical cells is Na-ß-Al₂O₃, which is an excellent sodium-ion conductor in the temperature range of the measurements. From the measured reversible emf, the activity of Na₂O in the Sb₂O₄-NaSbO₃ system has been calculated. The temperature dependence of the logarithm of the activity of Na₂O in various two-phase regions of the Sb₂O₄-NaSbO₃ system can be represented as
No thermodynamic data have been reported earlier in the literature for the system Sb₂O₄-NaSbO₃, and the present data constitute the first thermodynamic information.     

Catalytic decomposition of nitrous oxide N 2O: a study for p-block-element lead in PbO—ZrO2/Al2O3 systems

PbO—ZrO₂ catalysts have been prepared by sequential impregnation/calcination onto Al₂O₃ support for high concentration N₂O (27.97 mol%) decomposition. The p-block-element involved material system has been investigated with GC, BET, DTA, XRD and catalytic activity evaluation. It is found that with an atomic ratio Pb:Zr = 1:6 the material system shows the best catalytic performance for the decomposition. The catalyst with this composition has a tetragonal phase of ZrO₂ over reaction temperatures. The catalytic activity observed can be attributed to the presence of Pb cations with mixed valence states in tetragonal ZrO₂ lattice. Doping gases such as H₂O, CO₂, and O₂ are also mixed into the N₂O and studied. It is found that N₂O adsorption is rate-limiting step for the decomposition reaction. The reaction can be described as first order with respect to partial pressure of N₂O, considering that decomposition product O₂ exhibits no inhibition effect on the reaction in high conversion region.     

Preparation optimization of multilayer-structured SnO2–Sb–Ce/Ti electrode for efficient electrocatalytic oxidation of tetracycline in water

In this study, electrodeposition and thermal decomposition were alternatively used for the fabrication of a series of novel multilayer-structured SnO₂-Sb-Ce/Ti (SSCT) electrodes, and their physiochemical and electrochemical properties were investigated for electrochemical oxidation of tetracycline (TC) in aqueous medium. Experimentally, after the SnO₂-Sb-Ce (SSC) composite was electrodeposited for 120 s on the titanium substrate in aqueous solution, the outer thermal coatings composed of SSC were synthesized by a hydrothermal method. Both influences of electrodeposition time (T_ed) and thermal decomposition time (T_td) were investigated to obtain the optimum preparation. It was found that when increasing T_ed to a certain extent a longer lifetime of electrode can be achieved, which was attributed to a more solid interlayer structure. A notable SSCT_Ted,Ttd electrode, i.e., SSCT_3,10, which was prepared through three times of 120 s' electrodeposition (T_ed=3) and ten times of thermal decomposition (T_td=10) obtained the highest oxygen evolution potential 3.141 V vs. SCE. In this selected electrode, when 10 mg·L^-1 initial TC concentration was added to this wastewater, the highest color removal efficiency and mineralization rate of TC were 72.4% and 41.6%, respectively, with an applied electricity density of 20 mA·cm^-2 and treatment time of 1 h. These results presented here demonstrate that the combined application of electrodeposition and thermal decomposition is effective in realization of enhanced electrocatalytic oxidation activity.     

Phase Equilibria in the System ZrO2─InO1.5

Phase equilibria in the system ZrO₂─InO_1.5 have been investigated in the temperature range from 800° to 1700°C Up to 4 mol%, InO_1.5 is soluble in t -ZrO₂ at 1500°C. The martensitic transformation temperature m → t of ZrO₂ containing InO_1.5 is compared with that of ZrO₂ solid solutions with various other trivalent ions with different ionic radii. The diffusionless c → t ' A phase transformation is discussed. Extended solid solubility from 12.4 ± 0.8 to 56.5 ± 3 mol% InO_1.5 is found at 1700°C in the cubic ZrO₂ phase. The eutectoid composition and temperature for the decomposition of c -ZrO₂ solid solution into t -ZrO₂+InO_1.5 solid solutions were determined. A maximum of about 1 mol% ZrO₂ is soluble in bcc InO_1.5 phase. Metastable supersaturation of ZrO₂ in bcc InO _1.5 and conditions for phase separation are discussed.     

Gas-Sensing Properties of Spinodally Decomposed (Ti,Sn)O2 Thin Films

The gas-sensing properties of spinodally decomposed (Ti,Sn)O₂ thin films on sapphire substrates were investigated for CO, C₃H₈, and C₂H₅OH, and hydrogen gases at a temperature of 500°C. The variation in the d -spacing of the (101) plane of (Ti_0.5Sn_0.5)O₂ films showed behavior that was typical of spinodal decomposition during annealing at a temperature of 900°C. Transmission electron micrographs of the spinodally decomposed (Ti,Sn)O₂ films on sapphire (0112) substrates revealed the characteristic modulated structure. The modulated lamella microstructure consisted of TiO₂- and SnO₂-rich regions at intervals of ∼10 nm. The films were very sensitive to hydrogen gas and revealed anisotropic electrical conduction that was influenced by the modulated microstructure, which is characteristic of spinodal decomposition.     

Decomposition of Al2TiO5 and Al2(1-x)MgxTi(1+x)O5 Ceramics

The decomposition of Al_{2(1- x )}Mg _x Ti_{(1+ x )}O₅ ceramics in air has been studied between 900° and 1175°C for 0 lessthan equal to x lessthan equal to 0.6. The decomposition temperature versus composition x predicted using a thermodynamic model based on the regular solution approach is in satisfactory agreement with the experimental results. The decomposition kinetics has been studied at 1100°C for x = 0, 0.1, and 0.2 and follows a nucleation and growth mechanism. Random nucleation of the reaction products is hindered by the high elastic stresses that result from the molar volume change related to decomposition because of the small chemical driving force available. Decomposition occurs only at a limited number of sites, probably associated with the presence of impurities and/or glassy phase. The decomposition products grow as nodules formed by an Al₂O₃ (+ MgAl₂O₄ for x > 0) core and a TiO₂ shell. The growth is parabolic for x = 0 and linear for x = 0.1 and 0.2. The rate-controlling step in the decomposition mechanism of pure Al₂TiO₅ ( x = 0) is the transport of Al³⁺ ions through the TiO₂-rutile phase.     

Eutectoid Decomposition of MgO-Partially-Stabilized ZrO2

Euctectoid decomposition of cubic ( c ) ZrO₂ in MgO-partially-stabilized ZrO₂ (Mg-PSZ) has been studied using optical, scanning electron, and transmission electron microscopy. Alloys containing from 8.1 to 18.6 mol% MgO were decomposed by annealing between 1100° and 1300°C for times up to 16 h. The eutectoid products nucleated heterogeneously at the grain boundaries and advanced into the adjoining two-phase grains. Decomposition proceeded as a "cellular" reaction involving the cooperative growth of MgO and a low-solute ZrO₂ phase with either monoclinic ( m ) or tetragonal ( t ) symmetry. The MgO morphology is rodlike and exhibits a well-defined orientation relationship to m -ZrO₂. The rate of eutectoid decomposition was a maximum at 1200°C and was greater in the solute-rich materials at all temperatures. At 1100°C, SrO doping decreased the nucleation rate of the eutectoid product in a 9.7 mol% alloy, thus strongly suppressing the decomposition rates; at the higher decomposition temperatures, the SrO was less effective.     

Chemical Vapor Deposition of CuOx Films by Cul and O2: Role of Cluster Formation on Film Morphology

CuO _x films were deposited on silica substrates by the chemical vapor deposition (CVD) method, using CuI and O₂ as source gases at low pressure in a tubular reactor. The growth mechanism to obtain a dense and uniformly distributed (in the axial direction in a tubular reactor) film was investigated. It was found that the occurrence of homogenous nucleation caused an abrupt increase of deposition rate and made the film porous. Homogeneous nucleation can be prevented by properly selecting reactant concentration, reactor temperature, and reactor diameter. Based on an aerosol diffusion theory from laminar pipe flow, a method of predicting cluster size in this CVD reaction system was proposed. The result showed that the clusters formed by homogeneous nucleation had an average size of about 1 nm in diameter.     

Thermal Stability of Al3BC3

The thermal stability of Al₃BC₃ powder was analyzed. Nearly X-ray-pure Al₃BC₃ powder was obtained through the calcination of the aluminum, B₄C, and carbon mixture at 1800°C in Ar. In contrast to the former investigations, which reported the melting of so called "Al₈B₄C₇" at 1800°C, Al₃BC₃ did not melt up to 2100°C. Instead, it decomposed by the vaporization of aluminum. The decomposition occurred distinctly at 1400° and 1900°C in flowing Ar and a sealed carbon crucible, respectively. The results indicated that the decomposition temperature depended on the partial pressure of aluminum vapour in the atmosphere.     

Low-Pressure Chemical Vapor Deposition of α-Si3N4 from SiF4 and NH3: Kinetic Characteristics

Deposition of α-Si₃N₄ from SiF₄ and NH₃ was systematically studied using an axisymmetric, vertical hot-wall reactor in the temperature range of 1340° to 1490°C. The relationship between process variables and deposition behavior was identified. The deposition process was most strongly influenced by temperature. In general, deposition rate increased exponentially with increased deposition temperature, although reagent depletion in the axial direction caused a rapid decrease in the deposition rate. The deposition rate increased moderately with increased flow rate or decreased NH₃/SiF₄ molar ratio. The decomposition characteristic of pure NH₃ and SiF₄ were studied utilizing mass spectroscopy and compared to thermodynamic predictions in order to assess their influences on the Si₃N₄ deposition process. Finally, the crystallography of Si₃N₄ deposits was correlated as a function of temperature and deposition rate.     

Synthesis of MgAl2O4 Spinel Powder by Combination of Sol–Gel and Precipitation Processes

MgAl₂O₄ spinel precursor was prepared by a novel method combining a sol–gel process with the "traditional" precipitation process. The thermal decomposition and phase development of the precursor were analyzed, and the degree of agglomeration of the calcined powder was assessed by determining its particle size and crystal size. The optimum calcination temperature was determined based on the variation of specific surface areas, crystal size, and particle size. Completely crystallized ultrafine spinel powder ( d ₅₀=600 nm, specific surface area=105 m²/g) was obtained after calcination at 900°C.     

High-Intensity Discharge Lamp with Mo–SiO2 Functionally Graded Material

We show the invention of the new type of hermetically sealed high-intensity discharge lamps, made of Mo–SiO₂ functionally graded material (FGM) as an electrode and a sealing component. In the case of high-intensity discharge lamps with Mo–SiO₂ FGM (FGM lamp), the thermal expansion coefficient between Mo and SiO₂ is functionally graded so that it tolerates a large number of heating cycles, with no cooling system required. Furthermore, lamps survive without breakage. The W electrode is totally separated from the lamp envelope by the FGM, so that no leakage of the luminous elements or gases takes place, when a large gas pressure exists inside a lamp.     

Influence of the reaction conditions on the electrochemical promotion by potassium for the selective catalytic reduction of N2O by C3H6 on platinum

In this work, we have investigated for the first time the selective catalytic reduction of N₂O by C₃H₆ over an electrochemical catalyst (Pt/K-βAl₂O₃). It was evaluated the influence of the reaction conditions (temperature, oxygen concentration, water vapour presence and time on stream treatment under reaction conditions) on the catalytic performance of the electrochemical catalyst. Electrochemical pumping of potassium ions to the Pt catalyst working electrode strongly increased the N₂O reduction rate, activating the catalyst at lower temperatures. However, it was found that the efficiency of the electrochemical promotion decreased as the oxygen concentration increased because of a strong inhibition of propene adsorption and a relative increase of the oxygen coverage. On the contrary, the presence of potassium ions on the Pt catalyst strongly decreased the inhibiting effect of water vapour, increasing the catalytic activity of the catalyst. In addition, the catalyst stability was confirmed by a deactivation study. It was found that a long term treatment at high temperature under operating conditions had a positive effect on the efficiency of the Pt/K-βAl₂O₃ electrochemical catalyst.