Reduction of NiAl2O4 containing catalysts for steam methane reforming reaction

Reducibility of a NiAl₂O₄ containing catalyst was studied. On a measurement of NiAl₂O₄ concentration in a catalyst, a peak area ratio of NiAl₂O₄ in XRD analysis was verified to express the NiAl₂O₄ concentration. The reducibility of NiAl₂O₄ was confirmed to be dependent on the calcining temperature to form NiAl₂O₄, not dependent on the calcining time. The catalyst containing NiAl₂O₄ was ascertained to be reduced under convenient conditions to actual plant operations; H₂/N₂ = 30/70 at 1023K for 1 h + steam/CH₄ = 6 at 1023K for 17 h.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.     

Effects of ZrO2-promoter on catalytic performance of CuZnAlO catalysts for production of hydrogen by steam reforming of methanol

When ZrO₂-promoter was added to CuZnAlO catalyst, its methanol conversion H₂ yield and H₂ selectivity improved greatly during production of hydrogen by methanol steam reforming. Using COPZr-2 catalyst that expressed best catalytic performance as an example, the optimized reaction conditions were first confirmed. Then the 150 h stability test of COPZr-2 catalyst showed that the catalyst had good stability: methanol conversion and H₂ yield were kept at 88% and 83%, respectively; and outlet H₂ and CO content were >63% and 0.20–0.31%, respectively. A series of techniques, such as SEM, XRD, XPS, were used to characterize the catalysts with or without ZrO₂-promoter. SEM and XRD results show that ZrO₂-promoter can improve the dispersion of CuO and Cu crystallites. XPS results show that ZrO₂-promoter can lower Al content on the surface of catalyst in effect, and weaken the interaction between CuO and Al₂O₃ so as to avoid the generation of CuAl₂O₄ spinel-type compound.     

Hydrogen from steam reforming of ethanol. characterization and performance of copper-nickel supported catalysts

The effect of the copper loading and calcination temperature on the structure and performance of Cu/Ni|K|γ-Al₂O₃ catalysts is examined. TPR, XRD and N₂O chemisorption techniques are employed. Activity and selectivity measurements are carried out considering steam reforming of ethanol as the test reaction.

The appearance of CuO phase depends on copper loading and calcination temperature, whereas NiAl₂O₄ phase is present in all the analyzed samples. Copper dispersion is favored at lower copper loading. TOF values indicate that steam reforming of ethanol should be a structure-sensitivity reaction, at least under the experimental conditions used in this work.     

Energy-efficient conversion of propane to propylene and ethylene over a V2O5/CeO2/SA5205 catalyst in the presence of limited oxygen

Oxidative conversion of propane to propylene and ethylene over a V₂O₅/CeO₂/SA5205 (V:Ce=1:1) catalyst, with or without steam and limited O₂, has been studied at different temperatures (700–850 °C), C₃H₈/O₂ ratio (4.0), H₂O/C₃H₈ ratio (0.5) and space velocity (3000 cm³ g⁻¹ h⁻¹). The propane conversion, selectivity for propylene and net heat of reaction (ΔHr) are strongly influenced by the reaction temperature and presence of steam in the reactant feed. In the presence of steam and limited O₂, the process involves a coupling of endothermic thermal cracking and exothermic oxidative conversion reactions of propane which occur simultaneously. Because of the coupling of exothermic and endothermic reactions, the process operates in an energy-efficient and safe manner. The net heat of reaction can be controlled by the reaction temperature and concentration of O₂. The process exothermicity is found to be reduced drastically with increasing temperature. Due to the addition of steam in the feed, no coke formation was observed in the process.     

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

The preparation of LiCo_yMn_xNi_1−x−yO₂ from LiOH·H₂O, Ni(OH)₂ and γ-MnOOH in air was studied in detail. Single-phase LiCo_yMn_xNi_1−x−yO₂ (0y0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1z1.11 for y=0.2) and the Co doping level (0.05y0.2) do not significantly affect the discharge capacity of Li_zCo_yMn_0.2Ni_0.8−yO₂. The doping of Co into LiMn_0.2Ni_0.8O₂ accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn_0.2Ni_0.8O₂ is determined to be 4, the formation of a solid solution between LiCo_yNi_1−yO₂ and Li₂MnO₃ is confirmed.     

Preparation and electrochemical characteristics of LiNi1/3Mn1/3Co1/3O2 coated with metal oxides coating

LiNi_1/3Mn_1/3Co_1/3O₂ prepared by a spray drying method exhibited poor cyclic performance when it was operated at rates of 0.5C and 2C in 3–4.6 V. A metal oxide (ZrO₂, TiO₂, and Al₂O₃) coating (3 wt%) could effectively improve its cyclic performance at both 0.5C and 2C. Electrochemical impedance spectroscopy (EIS) studies suggested that both the surface resistance and the charge transfer resistance of the bare LiNi_1/3Mn_1/3Co_1/3O₂ significantly increase after 100 cycles, whose origin is mainly related to the change in both the particle surface and electrode morphologies. The presence of a thin metal oxide layer could remarkably suppress the increase in the total resistance (sum of the surface resistance and the charge transfer resistance), which was attributed to the improvement in good cyclic performances.     

Cycle characterizations of LiMxMn2−xO4 (M=Co, Ni) materials for lithium secondary battery at wide voltage region

LiM_xMn_2−xO₄ (M=Co, Ni) materials have been synthesized by a melt-impregnation method using γ-MnOOH as the manganese source. Highly crystallized LiM_xMn_2−xO₄ compounds were synthesized at a calcination temperature of 800°C for 24 h in air. All compounds show a single phase except for LiNi_0.5Mn_1.5O₄ based on the X-ray diffraction (XRD) diagram. With the increase of the doping content from 0.1 to 0.5, the capacity of doping materials decreases mainly in the 4 V region.

Although LiM_0.5Mn_1.5O₄ (M=Co, Ni) compound shows a small capacity in the (3+4) V region compared with parent LiMn₂O₄, it is a very effective material in reducing capacity loss in the 3 V region that is caused by the Jahn–Teller distortion. The doping of Co and Ni ions in the LiMn₂O₄ cathode material promotes the stability of this structure and provides an excellent cyclability.     

Effect of preparation conditions of CuO–CeO2–ZrO2 catalyst on CO removal from hydrogen-rich gas

The activities of CuO–CeO₂–ZrO₂ catalysts synthesized by four methods, e.g. sol–gel, co-precipitation, one-step impregnation, and two-step impregnation, were compared for CO removal from hydrogen-rich gas. The influence of the precipitant and calcination temperature on the catalytic activity was investigated, and a series of analytical methods, such as XRD, H₂-TPR, TG-DSC, and SEM, were used to characterize the catalysts. It was indicated that CuO–CeO₂–ZrO₂ catalyst prepared by co-precipitation method exhibits the widest operation temperature range with the 99% conversion of CO and relatively high selectivity. The optimized preparation conditions were confirmed using Na₂CO₃ as a precipitant, and calcining at 500 °C. It was proposed that the high activity and selectivity result from the high dispersion of copper and strong interaction among CuO, CeO₂, and ZrO₂. The effects of precipitants on the grain size and morphology of the catalyst is larger than that of calcination temperature.     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.     

Autothermal reforming of methane over Ni/γ-Al2O3 catalysts: the enhancement effect of small quantities of noble metals

The effect of introducing small amounts of Pt, Pd and Ir (<0.3% by weight) into Ni/γAl₂O₃ catalysts (15% Ni w/w) for the autothermal reforming of methane (ATR) was investigated. While the unpromoted catalyst took the partial oxidation of methane to equilibrium, the promoted ones increased the methane conversion in ATR. No electronic modifications of nickel sites were observed with the addition of noble metals, but they did cause an increase in metal surface area. The effect of noble metals on this reaction, under these conditions, was assigned to this expansion of the metal surface.     

Electrochemical characteristics and cycle performance of LiMn2O4/a-Si microbattery

A LiMn₂O₄ thin film and an amorphous Si (a-Si) thin film were prepared by radio-frequency (rf) magnetron sputtering. Each thin film was electrochemically evaluated by cyclic voltammetry (CV) and galvanostatic cycling. The rate of capacity fade on cycling was monitored as a function of the voltage window and current density. This was compared with the cycle performance of cathode and anode using two kinds of electrolyte, 1 M LiPF₆ in EC/DMC and PC, for 100 cycles. It was found that the discharge capacity of optimized LiMn₂O₄/a-Si full-cell reached 24 μAh/(cm²-μm) in the first cycle, and a reversible capacity of about 16 μAh/(cm² μm) was still maintained after 100 cycles. In a voltage window of 3.0–4.2 V, LiMn₂O₄/a-Si full-cell exhibits relatively stable cycle performance compared to a voltage window of 2.75–4.2 V.     

Electrochemical performance of Nd0.6Sr0.4Co0.5Fe0.5O3−δ–Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm⁻² at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes with 0.1 mg cm⁻² (0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ followed by firing at 700 °C (but the electrolyte–Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm⁻² at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.     

Preliminary attempt to enhance the hydrogenation of carbon dioxide to methane on cobalt oxide catalyst by adding CuO---ZnO---Cr2O3

Hydrogenation of carbon dioxide (CO₂) was carried out on cobalt oxide catalyst (Co₃O₄) at atmospheric pressure. The hydrogenation proceeded even at 473K. Total conversion reached a maximum (ca 55%) at 573K. Methane (ca 50%) and small amounts of CO (3–5%) were produced during the hydrogenation. It is indicated that the reaction proceeds on partially reduced Co₃O₄. An attempt to enhance the hydrogenation of CO₂ was carried out by adding CuO---ZnO---Cr₂O₃ as a cocatalyst and as a result, the yield of methane was selectively increased.     

Effect of Co content on performance of LiAl1/3−xCoxNi1/3Mn1/3O2 compounds for lithium-ion batteries

Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were studied via the combination of computational and experimental approach. The calculated voltage curve of LiNi_1/3Al_1/3Mn_1/3O₂ compound is presented, indicating it is of great potential for a cathode material of lithium-ion batteries. Unfortunately, it was found that the LiNi_1/3Al_1/3Mn_1/3O₂ compound without impurity phase could not be synthesized via a sol–gel process. To obtain a layered compound without impurity phase, partial of Al is replaced by Co in LiNi_1/3Al_1/3Mn_1/3O₂ compound in this study. Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were synthesized via sol–gel reaction at 900 °C under a oxygen stream. Single phase of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ in 1/6  x  1/3 region could be prepared successfully. The discharge capacity and conductivity increased with an increase in the Co-substitution content. The enhancement of the conductivity and phase purity by the introduction of Co content shows profound influence on the performance of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ compounds.     

Mo2C/Al2O3的制备及其催化二甲醚水蒸气重整性能研究

通过浸渍沉淀法结合程序升温碳化法制备了Mo₂C/Al₂O₃复合催化剂,并应用于二甲醚水蒸气重整催化体系的研究。考察了二甲醚水解催化载体、水解功能组分Al₂O₃与重整功能组分Mo₂C的比例、反应物浓度对复合催化剂活性的影响。结果表明,β-Mo₂C与γ-Al₂O₃载体以Mo/Al = 1/1耦合后能够高效催化二甲醚重整制氢,其最佳进料水醚比为5,最适反应温度为400℃。     

Effect of support on catalytic properties of Rh catalysts for steam reforming of 2-propanol

Catalytic performance of Rh catalyst supported on CeO₂, Al₂O₃, SiO₂, ZrO₂, MgO or TiO₂ for steam reforming of 2-propanol has been studied. The performance was greatly influenced by the type of the supports through interactions between Rh and supports. CeO₂-supported Rh catalyst resulted in the highest selectivity among the catalysts studied here. It probably has a longer catalytic life than Al₂O₃-supported catalysts actually known to be stable, because the amount of coke deposited on it was much smaller than that on the Al₂O₃-supported one. This mitigation of coke deposition has been explained by a reduction and oxidation cycle of CeO₂.     

Production of hydrogen for fuel cells by catalytic partial oxidation of ethanol over structured Ni catalysts

Cordierite monoliths, ceramic foams made from mullite and zirconia–alumina as well as γ-Al₂O₃ pellets were employed as supports for Ni/La₂O₃ structured catalysts for the production of hydrogen by catalytic partial oxidation of ethanol. Although all catalysts were very active for ethanol conversion and very selective towards the desired products, the one supported on the zirconia–alumina ceramic foam produced slightly better results. Tested under a wide variety of process conditions, the catalyst supported on the monolith exhibited excellent catalytic performance and long-term stability. In addition to this catalyst, which was prepared by washcoating the active phase on the support, catalysts were prepared on monoliths by adsorption and sol–gel techniques. Adsorption from solutions produced the catalyst with the weakest performance while the sol–gel method resulted in a catalyst with intriguing behavior. Overall, catalysts produced by washcoating on cordierite monoliths are the most promising candidates for the production of hydrogen by partial oxidation of ethanol. Other supports and preparation methods have the potential to produce better catalytic materials but require further optimization.     

Synthesis and electrochemical studies of the 4 V cathode, Li(Ni2/3Mn1/3)O2

Layered Li(Ni_2/3Mn_1/3)O₂ compounds are prepared by freeze-drying, mixed carbonate and molten salt methods at high temperature. The phases are characterized by X-ray diffraction, Rietveld refinement, and other methods. Electrochemical properties are studied versus Li-metal by charge–discharge cycling and cyclic voltammetry (CV). The compound prepared by the carbonate route shows a stable capacity of 145 (±3) mAh g⁻¹ up to 100 cycles in the range 2.5–4.3 V at 22 mA g⁻¹. In the range 2.5–4.4 V at 22 mA g⁻¹, the compound prepared by molten salt method has a stable capacity of 135 (±3) mAh g⁻¹ up to 50 cycles and retains 96% of this value after 100 cycles. Capacity-fading is observed in all the compounds when cycled in the range 2.5–4.5 V. All the compounds display a clear redox process at 3.65–4.0 V that corresponds to the Ni^2+/3+–Ni^3+/4+ couple.     

Effect of polymorphic phase transformations in Al2O3 film on oxidation kinetics of aluminum powders

Thermogravimetry was used to study the oxidation of aluminum powders at elevated temperatures. Aluminum powders of various particle sizes and surface morphologies were heated in oxygen up to 1500 °C at different heating rates. Partially oxidized samples were recovered from selected intermediate temperatures and the oxide phases present were analyzed by X-ray diffraction. The experimental data were related to current information on stabilities and phase changes of Al₂O₃ polymorphs. Aluminum powders were observed to oxidize in four distinct stages in the temperature range from 300 to 1500 °C. During stage I, from 300 to about 550 °C, the thickness of the natural amorphous alumina layer on the particle surface increases. The rate of this process is controlled by the outward diffusion of Al cations. At about 550 °C, when the oxide layer thickness exceeds the critical thickness of amorphous alumina of about 4 nm, the oxide transforms into γ-Al₂O₃. The specific volume of γ-Al₂O₃ is less than that of amorphous alumina; therefore, the newly formed γ-Al₂O₃ only partially covers the aluminum surface. The oxidation rate increases rapidly at the onset of stage II, but it decreases when the γ-Al₂O₃ layer becomes continuous. During stage III oxidation, the γ-Al₂O₃ layer grows and partially transforms into the structurally similar θ-Al₂O₃ polymorph. Finally, oxidation stage IV is observed after the transition to stable -Al₂O₃ results in an abrupt reduction of oxidation rate. Qualitative analysis of the rates of oxidation at the different stages enables one to understand the wide range of aluminum ignition temperatures observed for particles of different sizes.