An investigation on the reaction mechanism for the partial oxidation of methane to synthesis gas over platinum

The partial oxidation of methane to synthesis gas has been investigated by admitting pulses of pure methane, pure oxygen and mixtures of methane and oxygen to platinum sponge at temperatures ranging from 973 to 1073 K. On reduced platinum the decomposition of methane results in the formation of surface carbon and hydrogen. No deposition of carbon occurs during the interaction of methane with a partly oxidised catalyst. Oxygen is present in three different forms under the conditions studied: platinum oxide, dissolved oxygen and chemisorbed oxygen species. Carbon monoxide and hydrogen are produced directly from methane via oxygen present as platinum oxide. Activation of methane involving dissolved oxygen provides a parallel route to carbon dioxide and water. Both platinum oxide and chemisorbed oxygen species are involved in the oxidation of carbon monoxide and hydrogen. In the presence of both methane and dioxygen at a stoichiometric feed ratio the dominant pathways are the direct formation of CO and H₂ followed by their consecutive oxidation. A Mars-van Krevelen redox cycle is postulated for the partial oxidation of methane: the oxidation of methane is accompanied by the reduction of platinum oxide, which is reoxidised by incorporation of dioxygen into the catalyst.     

Partial oxidation of methane over platinum metal gauze

The partial oxidation of methane to synthesis gas has been studied over a platinum gauze catalyst. The experiments were carried out at atmospheric pressure with a single gauze in a quartz reactor heated in an electric furnace. The furnace temperature was varied in the range 200–900°C and the space time in the range 0.00021–0.00042 s. The feed consisted of a mixture of CH₄O₂Ar2110 and carbon oxides and water were the main products. Oxygen was only partly consumed and relatively small amounts of hydrogen were formed.     

Electrocatalytic methane coupling in the absence of oxygen on a high-temperature proton-conducting electrolyte

Electrocatalytic reaction of methane on the La_0.6Sr_0.4MnO₃ (LSM) anode of electrochemical cells based on SrO(CeO₂)_0.95(YbO_1.5)_0.05 (SCY) as a high-temperature, proton-conducting solid-electrolyte yields ethane and ethylene. Electric current is generated at zero voltage when methane is present in the anode compartment.     

Electrochemical investigation of platinum electrode in solid electrolyte cell

Electro-oxidation of platinum film electrode deposited on yttria-stabilized zirconia (YSZ) is examined in situ using potential programmed voltammetry at 450 °C in oxygen containing atmosphere. Under prolonged anodic oxidation different sorts of oxidized species are formed which are consumed subsequently during a linear cathodic potential scan resulting in three distinct reduction peaks, one of them being fairly reversible while the two others strongly irreversible. Higher oxidation potential and longer time of polarization favor the irreversible processes. The coexistence of three electrochemical processes is explained with the extension of the triple phase boundary. The rapid first process is identified as formation of PtO_x at the electrode/metal interface, the second process - a much slower, parallel one - is related to the phenomenon of oxygen backspillover at the metal/gas interface, and the slowest third process - consecutive to the first one - is attributed to growth of the PtO_x layer at the electrode/metal interface toward the bulk of the metal by analogy to electro-oxidation of platinum in aqueous liquid electrochemistry.     

聚合物基镁离子固态电解质的研究进展Q

镁离子电池因其比容量高、资源丰富、环境友好、安全性高(无枝晶)等优势,在储能电池领域脱颖而出.然而,镁金属负极在液态电解质中易钝化,导致其电化学性能不佳.因此,开发高效适用的固态电解质对实现高性能、实用化镁离子电池至关重要.聚合物电解质具有优异的机械稳定性、电化学稳定性、热稳定性且离子电导率高、成本低.但镁离子较高的电荷密度和较强的溶剂化作用限制了其在固态电解质中的解离与扩散.从纯固态聚合物电解质、凝胶聚合物电解质、复合聚合物电解质3个方面综述了国内外聚合物基镁离子固态电解质的离子电导率对解决镁金属负极钝化效应的贡献及其应用研究进展,指出聚合物基镁离子固态电解质当前面临的挑战并对其研究方向进行了建议和展望.     

The effect of electrochemical oxygen pumping on the rate of CO oxidation on Au electrode-catalyst

The effect of electrochemical pumping of oxygen on the rate of carbon monoxide oxidation on Au electrode-catalyst in a solid oxygen conducting electrolyte cell has been demonstrated. The induced change in the reaction rate at the cathodic polarization of an Au electrode was an order of magnitude higher than the rate of O^2– pumping from the reaction zone through the electrolyte. The anodic polarization of the Au electrode (O^2– pumping to the reaction zone through the electrolyte) caused purely Faradaic changes in the reaction rate.     

锂离子电池用固态电解质的研究现状与展望

目前商业化的锂离子电池多使用有机液态电解质,存在易燃易爆、易泄露等安全风险,而采用固态电解质替代有机液态电解质可以有效提高电池安全性。锂离子电池用固态电解质又可分为无机固态电解质和有机——即聚合物固态电解质。无机固态电解质对高温或其他腐蚀性环境适应性好,适用于在极端工作环境中刚性电池等领域;聚合物固态电解质在柔韧性和可加工性上则优势明显,适用于柔性电池等领域,但这些材料均尚有问题待解决。无机-有机复合的方式,有望综合两种材料的优势,取长补短,提高固态电解质的综合性能和实用价值。     

A high-performance solid oxide fuel cell with a layered electrolyte for reduced temperatures

The application of conventional zirconia-based electrolytes is limited to relatively high temperatures (ie > 750°C) due to their poor conductivities at low temperatures. Doped ceria has much higher conductivities; however, when exposed to fuel, electronic current develops within the material, which impairs cell performance and efficiency. Herein, we report a novel layered electrolyte structure consisting of a 10 µm samaria-doped ceria primary layer and a 2 µm scandia-ceria-stabilized zirconia protection layer on the fuel side. The cell had five layers and was fabricated using a tape casting and ultrasonic spraying technique. By carefully selecting the raw materials, the bilyer electrolyte was sintered to full density at a low temperature of 1250°C. The adverse interdiffusion and undesirable reactions between the two layers were largely avoided. A fuel cell with the layered electrolyte structure, operated on hydrogen fuel, produced a high open circuit voltage 1.07 V and a power density of 321 mW/cm² at 0.8 V and 600°C, 76% improvement compared to the fuel cell with a scandia-stabilized zirconia/samaria-doped ceria bilayer electrolyte reported in literature.     

Quasicatalytic and catalytic selective oxidation of methane to methanol over solid materials: a review on the roles of water

ABSTRACT

To date, although no commercial process for the selective oxidation of methane has been realized, various novel processes with effective solid materials operated at low temperature have been proposed. It is found that the addition of water in any processes not only influences the activity, selectivity, and stability of the solid materials but also affects the extraction efficiency of methanol from the product. Herein, the published results on the roles of water in the methanol production via the quasicatalytic and catalytic selective methane oxidation process using various solid materials in gas and liquid phases at low temperatures are critically reviewed.     

Partial oxidation of methane over nickel-added strontium phosphate

It was found that nickel-added strontium phosphate exhibited high activity and selectivity in partial oxidation of methane. The optimum nickel content could be determined. Over the optimum catalyst, methane conversions and H₂ and CO concentrations in excess of those predicted by the thermodynamic equilibrium were observed. It is believed that the catalytically active species is metallic nickel. This metallic nickel is considered to come from nickel-substituted strontium phosphate under reducing environment, giving highly dispersed nickel metal particles.     

阻燃聚氨酯基固态聚合物电解的制备

摘要：以聚己二酸-1,4-丁二醇酯二醇( PBA) 、六亚甲基二异氰酸酯( HDI)和阻燃剂N，N阻双（2（羟乙基）胺基亚甲基磷酸二乙酯( FCR-6）为主要原料合成阻燃聚氨酯（TPUP），将阻燃聚氨酯与锂盐复合得到阻燃聚氨酯基固态聚合物电解质。采用红外光谱、热重分析、锥形量热、力学测试、电化学窗口、电导率和电池的充放电性能测试等对阻燃聚氨酯基固态聚合物电解质进行了表征和性能测试。研究表明，TPUP具有良好阻燃性能，制备的阻燃电解质TPUP25%Li综合性能最佳，且拉伸强度达到2.09MPa，80℃时离子电导率为3.09M10-4 S/cm，以阻燃电解质组装的全固态锂电池，在80℃时0.2C电流密度下放电容量达到159mA?h/g。     

Acid-base properties and the directions of oxidative transformation of methane over nickel-based catalysts

The reactions of dry (CO₂) reforming and partial oxidation of methane have been investigated in a membrane reactor. The membrane is composed of a dense thin silica (SiO₂) film supported on porous Vycor tubes and was synthesized by chemical vapor deposition. The hydrogen permeance of the membrane was 0.2–0.3 cm³/(cm² min atm) at 600°C combined with a H₂/N₂ selectivity of 200–300. Significant increases in methane conversion were attained in both reactions at 500–750°C, albeit at very low space velocities. The membrane permeance declined by 50% after exposure to feeds containing H₂O, but otherwise exhibited excellent stability under reaction conditions.     

The selective oxidation of methane to ethane and ethylene in a solid oxide electrolyte reactor

A study of the selective oxidative coupling of methane (OCM) to C₂ hydrocarbons (ethane and ethylene) in a solid-state electrochemical reactor made from yttria-stabilized zirconia (YSZ) has been made. Three different catalyst–electrode systems based on silver and two trimetallic formulations of Mn modified alkali (Na and K) tungstates supported on silica were used. A comparison is made between co-fed and electrochemically-supplied oxygen. The electrochemically-supplied oxygen gave higher overall C₂ selectivities than the co-fed method under low current conditions, which was attributed to differences in local methane to oxygen ratios at the catalyst surface. The potassium tungstate supported catalyst gave the best overall C₂ selectivity (86% at 4% C₂ yield).     

Oxidative conversion of methane to syngas over NiO/MgO solid solution supported on low surface area catalyst carrier

Influence of time-on-stream (0.5–15 h), CH₄/O₂ ratio in feed (1.8–8.0), space velocity (6000–510,000 cm³ g⁻¹ h⁻¹), catalyst particle size (22–70 mesh), and catalyst dilution by inert solid particles (diluent/catalyst weight ratio=4) on the performance at different temperatures (600–900°C) of the NiO/MgO solid solution deposited on SA-5205 [which is a low surface area macroporous silica-alumina catalyst carrier] in the oxidative conversion of methane to syngas (a mixture of CO and H₂) has been investigated. The dependence of conversion and selectivity on the space velocity is strongly influenced by the temperature. Both the conversion and selectivity for H₂ and CO are decreased markedly by increasing the CH₄/O₂ ratio in the feed. The catalyst dilution resulted in a small but significant decrease in both the conversion and selectivity for H₂ and CO. The increase in the catalyst particle size had also a small but significant effect on both the conversion and selectivity in the oxidative conversion process. Both the heat and mass transfer processes seem to play significant roles in the oxidative conversion of methane to syngas at a very low contact time or very high space velocity (5.1×10⁵ cm³ g⁻¹ h⁻¹).     

New solid polymer electrolyte membranes for alkaline fuel cells

New solid polymer electrolyte composite membranes have been prepared using chitosan as matrices and incorporating potassium hydroxide as the functional ionic source. These membranes were featured as a three‐layer structure having a porous intermediate layer while the two crosslinked surface layers are dense. Results from impedance spectroscopy analysis showed that the conductivity of some hydrated composite membranes, after hydration for 1 h at room temperature, reached about 10⁻² S cm⁻¹. Several composite membranes were then tested in alkaline fuel cells, using hydrogen as fuel, air as oxidant and platinum as the electrode catalyst. A current density of 35 mA cm⁻² has been achieved at 60 °C with a flow rate of hydrogen at 50 ml min⁻¹ and air at 200 ml min⁻¹. Copyright © 2004 Society of Chemical Industry     

负载型钯催化剂上甲烷催化燃烧的研究进展

概述了负载型钯催化剂对甲烷完全氧化的催化机理,以及钯催化剂在甲烷催化燃烧中的性能特点。     

Partial oxidation of methane to synthesis gas over Rh-hexaaluminate-based catalysts

The partial oxidation of methane to synthesis gas over catalysts consisting of Rh supported on hexaaluminates (BaAl₁₂O₁₉, CaAl₁₂O₁₉ and SrAl₁₂O₁₉) was investigated at atmospheric pressure and high reactant dilution in order to compare their performances within the kinetic-controlling regime. Comparison with the results obtained over a commercial Rh/-Al₂O₃ system indicates that hexaaluminate catalysts are active and selective in this reaction. Despite of the higher surface area of the support, hexaaluminate-supported catalysts were found less stable, active and selective than an -Al₂O₃-supported catalyst.     

Partial oxidation of methane over rhodium catalysts for power generation applications

The partial oxidation of methane (POM) to syngas, i.e. H₂ and CO, over supported Rh catalysts was investigated at atmospheric pressure. The influence of support material, Rh loading and the presence of water vapor on the methane conversion efficiency and the product gas composition was studied. The catalysts containing ceria in the support material showed the highest activity and formation of H₂ and CO. By increasing the Rh loading, a decrease of the ignition temperature was obtained. The addition of water vapor to the reactant gas mixture was found to increase the ignition temperature and the formation of hydrogen, which is favorable for combustion applications where the catalytic POM stage is followed by H₂-stabilized homogeneous combustion.     

Synthesis gas formation by direct oxidation of methane over Rh monoliths

The production of H₂ and CO by catalytic partial oxidation of CH₄ in air or O₂ at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10^–4 and 10^–2 s and compared to previously reported results for Pt-coated monoliths. Using O₂, selectivities for H₂ ( ) as high as 90% and CO selectivities (S _CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O₂ instead of air. The superiority of Rh over Pt for H₂ generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H₂ than on Pt, on which the O+ H OH reaction is much faster.This research was partially supported by DOE under Grant No. DE-FG02-88ER13878-AO2.     

Performance of a direct methanol fuel cell

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.