Electrochemical reduction of carbon dioxide to ethylene at a copper electrode in methanol using potassium hydroxide and rubidium hydroxide supporting electrolytes

The electrochemical reduction of CO₂ with a Cu electrode was investigated in methanol using potassium hydroxide and rubidium hydroxide supporting salts. The main products from CO₂ were methane, ethylene, carbon monoxide and formic acid. The maximum current efficiency for ethylene was of 37.5%, at −4.0 V versus Ag/AgCl, saturated KCl in KOH/methanol. The typical ratios of current efficiency for ethylene/methane, r_f(C₂H₄)/r_f(CH₄), were 2.3 and 6.7, in KOH/methanol and RbOH/methanol-based electrolytes, respectively. In KOH/methanol, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was depressed to below 3.3%. On the basis of this work, the high efficiency electrochemical CO₂-to-ethylene conversion method appears to be achieved. Future work to advance this technology may include the use of solar energy as the electric energy source. This research can contribute to the large-scale manufacturing of fuel gases from readily available and inexpensive raw materials, CO₂-saturated methanol from industrial absorbers (the Rectisol process).     

Electrochemical reduction of high pressure CO2 at a Cu electrode in cold methanol

The electrochemical reduction of high pressure CO₂ with a Cu electrode in cold methanol was investigated. A high pressure stainless steel vessel, with a divided H-type glass cell, was employed. The main products from CO₂ by the electrochemical reduction were methane, ethylene, carbon monoxide and formic acid. In the electrolysis of high pressure CO₂ at low temperature, the reduction products were formed in the order of carbon monoxide, methane, formic acid and ethylene. The best current efficiency of methane was of 20% at −3.0 V. The maximum partial current density for CO₂ reduction was approximately 15 mA cm⁻². The partial current density ratio of CO₂ reduction and hydrogen evolution, i(CO₂)/i(H₂), was more than 2.6 at potentials more positive than −3.0 V. This work can contribute to the large-scale manufacturing of fuel gases from readily available and inexpensive raw materials, CO₂-saturated methanol from industrial absorbers (the Rectisol process).     

Electrochemical conversion of carbon dioxide to methane in aqueous NaHCO3 solution at less than 273 K

The electrochemical reduction of CO₂ on a Cu electrode was investigated in aqueous NaHCO₃ solution, at low temperature. A divided H-type cell was employed, the catholyte was 0.65 mol dm⁻³ NaHCO₃ aqueous solution and the anolyte was 1.1 mol dm⁻³ KHCO₃ aqueous solution. The temperature during the electrolysis of CO₂ was decreased stepwise to 271 K. Methane and formic acid were obtained as the main products. The maximum Faradaic efficiency of methane was 46% at −2.0 V and 271 K. The efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was significantly depressed with decreasing temperature. Based on the results of this work, the proposed electrochemical method appears to be a viable means for removing CO₂ from the atmosphere and converting it into more valuable chemicals. The synthesis of methane by the electrochemical method might be of practical interest for fuel production and the storage of solar energy.     

The Electro-Reduction of Carbon Dioxide in a Continuous Reactor

This paper reports an investigation into the electro-reduction of CO₂ in a laboratory bench-scale continuous reactor with co-current flow of reactant gas and catholyte liquid through a flow-by 3D cathode of 30^# mesh tinned-copper. Factorial and parametric experiments were carried out in this apparatus with the variables: current (1–8 A), gas phase CO₂ concentration (16–100 vol%) and operating time (10–180 min), using a cathode feed of [CO₂ + N₂] gas and 0.45 m KHCO₃(aq) with an anolyte feed of 1 m KOH(aq), in operation near ambient conditions (ca. 115 kPa(abs), 300 K). The primary and secondary reactions here were respectively the reduction of CO₂ to formate (HCOO⁻) and of water to hydrogen, while up to ca. 5% of the current went to production of CO, CH₄ and C₂H₄. The current efficiency for formate depended on the current density and CO₂ pressure, coupled with the hydrogen over-potential plus mass transfer capacity of the cathode, and decreased with operating time, as tin was lost from the cathode surface. For superficial current densities ranging from 0.22 to 1.78 kA m⁻², the measured values of the performance indicators are: current efficiency for HCOO⁻ = 86–13%, reactor voltage = 3–6 Volt, specific energy for HCOO⁻ = 300–1300 kWh kmol⁻¹, space-time yield of HCOO⁻ = 2 × 10⁻⁴–6 × 10⁻⁴ kmol m⁻³ s⁻¹, conversion of CO₂ = 20–80% and yield of organic products from CO₂ = 6–17%.     

Oscillation of electrical current during direct methane oxidation over Ni-added LSCF–GDC anode of solid oxide fuel cells

Solid oxide fuel cells are studied under direct methane feeding with 10–70% CH₄. When either La_0.58Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)–Ce_0.9Gd_0.1O_1.95 (GDC) or Ni-added LSCF–GDC composite is used as the anode, the oscillations of the electrical current and the formation rates of CO and CO₂ occur. The oscillation of the electrical current can be explained by a mechanism of periodic oxidation–reduction of the bulk lattice of the anode, with the determining factor being the build-up of the concentration of the oxygen vacancies to a certain extent. As the methane concentration increases, the current density increases and becomes larger with Ni addition. Higher methane concentration leads to higher possibility to induce the oscillation, to start it earlier, and to result in a larger amplitude. Ni addition inhibites the occurrence of the oscillation of the electrical current but promotes that of the CO₂ formation rate.     

Electrochemical promotion of toluene combustion on an inexpensive metallic catalyst

Electrochemical promotion of the complete catalytic oxidation of toluene at 310 °C is reported, using a Ag/YSZ/Ag two electrode system where Ag films were deposited on YSZ from AgNO₃ aqueous solution followed by reduction in H₂. After on-stream activation, a non-negligible conversion (about 30%) at OCV is reached and then the rate of the catalytic toluene conversion into CO₂ and H₂O can be multiplied by a factor higher than 1.5, by application of a small negative current (about—4 μA cm⁻²). The associated Faradaic efficiency is very high and may exceed −13,000.     

Thermodynamic performance of O2/CO2 gas turbine cycle with chemical recuperation by CO2-reforming of methane

This paper proposes a novel power cycle system composed of chemical recuperative cycle with CO₂–NG (natural gas) reforming and an ammonia absorption refrigeration cycle. In which, the heat is recovered from the turbine exhaust to drive CO₂–NG reformer firstly, and then lower temperature heat from the turbine exhaust is provided with the ammonia absorption refrigeration system to generate chilled media, which is used to cool the turbine inlet gas except export. In this paper, a detailed thermodynamic analysis is carried out to reveal the performance of the proposed cycle and the influence of key parameters on performance is discussed. Based on 1 kg s⁻¹ of methane feedstock and the turbine inlet temperature of 1573 K, the simulation results shown that the optimized net power generation efficiency of the cycle rises up to 49.6% on the low-heating value and the exergy efficiency 47.9%, the new cycle system reached the net electric-power production 24.799 MW, the export chilled load 0.609 MW and 2.743 kg s⁻¹ liquid CO₂ was captured, achieved the goal of CO₂ and NO_x zero-emission.     

钙钛矿型混合导体透氧膜SrFe0.6Cu0.3Ti0.1O3－δ的制备与表征

Dense membrane with the composition of SrFe0.6Cu0.3Ti0.1O3-δ （SFCTO） was prepared by solid state reaction method. Oxygen permeation flux through this membrane was investigated at operating temperature ranging from 750℃ to 950℃ and different oxygen partial pressure. XRD measurements indicated that the compound was able to form single-phased perovskite structure in which part of Fe was replaced by Cu and Ti. The oxygen desorption and the reducibility of SFCTO powder were characterized by thermogravimetric analysis and temperature programmed reduction analysis, respectively. It was found that SFCTO had good structure stability under low oxygen pressure at high temperature. The addition of Ti increased the reduction temperature of Cu and Fe. Performance tests showed that the oxygen permeation flux through a 1.5 mm thick SFCTO membrane was 0.35-0.96 ml·min ^-1·cm^-2 under air/helium oxygen partial pressure gradient with activation energy of 53.2 kJ·mol^-1. The methane conversion of 85%, CO selectivity of 90% and comparatively higher oxygen permeation flux of 5 ml·min^-1·cm^- 2 were achieved at 850℃, when a SFCTO membrane reactor loaded with Ni-Ce/Al2O3 catalyst was applied for the partial oxidation of methane to syngas.     

Coupling of highly exothermic and endothermic reactions in a metallic monolith catalyst reactor: A preliminary experimental study

An LaFe_0.5Mg_0.5O₃/Al₂O₃/FeCrAl metallic monolith catalyst for the exothermic catalytic combustion of methane and an Ni/SBA-15/Al₂O₃/FeCrAl metallic monolith catalyst for the endothermic reforming of methane with CO₂ have been prepared. A laboratory-scale tubular jacket reactor with the Ni/SBA-15/Al₂O₃/FeCrAl catalyst packed into its outer jacket and the LaFe_0.5Mg_0.5O₃/Al₂O₃/FeCrAl catalyst packed into its inner tube was devised and constructed. The reactor allows a coupling of the exothermic and endothermic reactions by virtue of their thermal matching. An experimental study in which the temperature difference between the chamber of the external electric furnace and the metallic monolith catalyst bed in the jacket was kept very small, by adjusting the power supply to the furnace, confirmed that the heat absorbed in the reforming reaction does indeed partly come from that evolved in the catalytic combustion of methane, and that the direct thermal coupling of the two reactions in the reactor can be realized in practice. When the temperature of the electric furnace chamber was 1088 K, and the gas hourly space velocities (GHSVs) of the reactant mixtures passed through the inner tube and the jacket were 382 h⁻¹ and 40 h⁻¹, respectively, the conversions of methane and CO₂ in the reforming reaction were 93.6% and 91.7%, respectively, and the heat efficiency reached 81.9%. Stability tests showed that neither catalyst underwent deactivation during 150 h on stream.     

Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

Synthesis of a highly active carbon-supported Ir–V/C catalyst for the hydrogen oxidation reaction in PEMFC

The active, carbon-supported Ir and Ir–V nanoclusters with well-controlled particle size, dispersity, and composition uniformity, have been synthesized via an ethylene glycol method using IrCl₃ and NH₄VO₃ as the Ir and V precursors. The nanostructured catalysts were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The catalytic activities of these carbon-supported nanoclusters were screened by applying on-line cyclic voltammetry and electrochemical impedance spectroscopy techniques, which were used to characterize the electrochemical properties of fuel cells using several anode Ir/C and Ir–V/C catalysts. It was found that Ir/C and Ir–V/C catalysts affect the performance of electrocatalysts significantly based on the discharge characteristics of the fuel cell. The catalyst Ir–V/C at 40 wt.% displayed the highest catalytic activity to hydrogen oxidation reaction and, therefore, high cell performance is achieved which results in a maximum power density of 563 mW cm⁻² at 0.512 V and 70 °C in a real H₂/air fuel cell. This performance is 20% higher as compared to the commercial available Pt/C catalyst. Fuel cell life test at a constant current density of 1000 mA cm⁻² in a H₂/O₂ condition shows good stability of anode Ir–V/C after 100 h of continuous operation.     

Effect of Co and Rh promoter on NOx storage and reduction over Pt/BaO/Al2O3 catalyst

Effect of cobalt and rhodium promoter on NO_x storage and reduction (NSR) kinetics was investigated over Pt/BaO/Al₂O₃. Kinetics of 2% cobalt loading over Pt/BaO/Al₂O₃ demonstrated highest NO_x uptake during lean cycle, while reduction efficiency during rich cycle appeared most poor. In contrast to this, rhodium showed suppressing effect of NO_x uptake during lean cycle and demonstrated an enhanced effect for the higher efficiency of NO_x reduction during rich cycle. DRIFT study for NO_x uptake and regeneration confirmed formation of surface BaNO_x from the band at 1300 cm⁻¹ and formation of bulk BaNO_x from the band at 1330 cm⁻¹.     

Raman studies of peroxide formation,decomposition, and reduction on Ba/MgO

Ba/MgO is an active catalyst for the oxidative coupling of methane to form ethane and ethylene. It has been proposed that activation of methane occurs via reaction with peroxide species present at the surface of the catalyst. In the present work, Raman spectroscopy has been used to investigate the formation, decomposition, and reduction of BaO₂ on 4 mol% Ba/MgO. The presence of BaO₂ is evidenced by the presence of a band at 842 cm^–1. The peroxide forms above 300°C but is stable to decomposition at temperatures up to 500°C. Reduction of BaO₂ to BaO proceeds via Ba(OH)₂. BaCO₃ forms when either BaO or BaO₂ is exposed to CO₂. Once formed, BaCO₃ is stable to decomposition in He or O₂ at temperatures up to 500°C. Only BaCO₃ is observed when a mixture of CH₄ and O₂ is passed over the catalyst at 500°C.     

Thermodynamic analysis of carbon dioxide reforming of methane in view of solid carbon formation

A thermodynamic equilibrium analysis on the multi-reaction system for carbon dioxide reforming of methane in view of carbon formation was performed with Aspen plus based on direct minimization of Gibbs free energy method. The effects of CO₂/CH₄ ratio (0.5-3), reaction temperature (573-1473 K) and pressure (1-25 atm) on equilibrium conversions, product compositions and solid carbon were studied. Numerical analysis revealed that the optimal working conditions for syngas production in Fischer-Tropsch synthesis were at temperatures higher than 1173 K for CO₂/CH₄ ratio being 1 at which about 4 mol of syngas (H₂/CO = 1) could be produced from 2 mol of reactants with negligible amount of carbon formation. Although temperatures above 973 K had suppressed the carbon formation, the moles of water formed increased especially at higher CO₂/CH₄ ratios (being 2 and 3). The increment could be attributed to RWGS reaction attested by the enhanced number of CO moles, declined H₂ moles and gradual increment of CO₂ conversion. The simulated reactant conversions and product distribution were compared with experimental results in the literatures to study the differences between the real behavior and thermodynamic equilibrium profile of CO₂ reforming of methane. The potential of producing decent yields of ethylene, ethane, methanol and dimethyl ether seemed to depend on active and selective catalysts. Higher pressures suppressed the effect of temperature on reactant conversion, augmented carbon deposition and decreased CO and H₂ production due to methane decomposition and CO disproportionation reactions. Analysis of oxidative CO₂ reforming of methane with equal amount of CH₄ and CO₂ revealed reactant conversions and syngas yields above 90% corresponded to the optimal operating temperature and feed ratio of 1073 K and CO₂:CH₄:O₂ = 1:1:0.1, respectively. The H₂/CO ratio was maintained at unity while water formation was minimized and solid carbon eliminated.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Carbon-free dry reforming of methane to syngas over NdCoO3 perovskite-type mixed metal oxide catalyst

CoNdO_x (Co/Nd = 1) is a highly promising catalyst for the carbon-free CO₂ reforming of methane. Influence of the Co/Nd ratio on the catalyst performance in the CO₂ reforming and also on the crystalline phases and reduction by temperature programmed reduction (TPR) of the CoNdO_x catalyst has also been investigated. The CoNdO_x (CoNd = 1.0) catalyst consisted of mainly NdCoO₃ perovskite-type mixed metal oxide and it showed not only a high resistance to carbon formation at different process conditions (viz. temperature = 750–900 °C and gas hourly space velocity (GHSV) = 10000–50000 cm³ g^–1 h^–1) but also high activity and selectivity in the CO₂ reforming process. The high resistance to carbon formation for this catalyst is attributed mostly to strong metal (Co°)–support (Nd₂O₃) interactions.     

MoOx-based catalysts for the oxidative dehydrogenation (ODH) of ethane to ethylene: Influence of vanadium and phosphorus on physicochemical and catalytic properties

The influence of vanadium and phosphorus on the physicochemical properties of the MoO_x oxide and on its catalytic properties in the oxidation of ethane to ethylene is examined. A series of MoO_x, MoVO_x (Mo/V = 11) and MoVPO_x (Mo/V = 11, V/P = 1) catalysts were prepared, characterized by several techniques (BET, XRD, XPS, LRS and ATG) and studied in the oxidative dehydrogenation of ethane to ethene at atmospheric pressure and at the temperature of reaction of 550 °C. Their structural properties, during reduction and re-oxidation, were examined by in situ X-ray diffraction and by X-ray photoelectron spectroscopy after pre-treatment. The sample containing phosphorus is the most active (conversion 14%) and selective to ethylene (SC₂H₄ = 67%). The formation of [PMo₁₁VO₄₀]⁴⁻ is assumed during preparation, and its decomposition during calcination leads to well dispersed phosphate groups and improved interactions between Mo and V species. During the catalytic reaction Mo^VI is stabilised by means of solid solutions of V in Mo₅O₁₄ and in MoO₃ (V_xMo_1−xO_3−x/2). A synergetic effect between these two phases could be responsible for the best performance of Mo₁₁VPO_x as compared to those of MoO_x and Mo₁₁VO_x.     

Bimetallic catalysts for the catalytic combustion of methane using microreactor technology

Pt–W and Pt–Mo based catalysts were evaluated for methane combustion using a sandwich-type microreactor. Alumina washcoated microchannels were impregnated with platinum in combination with and promoted with tungsten and molybdenum and compared with commercially available Pt/Al₂O₃ catalysts. Catalysts were tested in the range of 300–700 °C with flow rates adjusted to GHSV of 74,000 h⁻¹ and WHSV of 316 L h⁻¹ g⁻¹. Catalysts containing tungsten were found to be the most active and the most stable possibly due to a metal interaction effect. A Pt–W/γ-Al₂O₃ containing 4.6 wt% Pt and 9 wt% W displayed the highest activity with full conversion at 600 °C and a selectivity to CO₂ of 99%.     

C,CO and CO2 hydrogenation on cobalt foil model catalysts: evidence for the need of CoO reduction

The hydrogenation of C, CO, and CO₂ has been studied on polycrystalline cobalt foils using a combination of UHV studies and atmospheric pressure reactions in temperature range from 475 to 575 K at 101 kPa total pressure. The reactions produce mainly methane but with selectivities of 98, 80, and 99 wt% at 525 K for C, CO, and CO₂, respectively. In the C and CO₂ hydrogenation the rest is ethane, whereas in CO hydrogenation hydrocarbons up to C₄ were detected. The activation energies of methane formation are 57, 86, and 158 kJ/mol from C, CO, and CO₂, respectively. The partial pressure dependencies of the CO and CO₂ hydrogenation indicate roughly first order dependence on hydrogen pressure (1.5 and 0.9), negative first order on CO (–0.75) and zero order on CO₂ (–0.05). Post reaction spectroscopy revealed carbon deposition from CO and oxygen deposition from CO₂ on the surface above 540 K. The reduction of cobalt oxide formed after dissociation of C-O bonds on the surface is proposed to be the rate limiting step in CO and CO₂ hydrogenation.     

Correlation of methane uptake with microporosity and surface area of chemically activated carbons

Two series of activated carbon discs have been prepared by chemical activation of olive stones with ZnCl₂ and H₃PO₄. Some of the carbons have been post-treated in order to modify their porous texture and/or surface chemical composition. All carbons have been characterized by adsorption of N₂ (−196 °C) and CO₂ (0 °C) and immersion calorimetry into dichloromethane. The volume of methane adsorbed at 25 °C and 3.5 MPa is proportional to the surface area deduced from immersion calorimetry into dichloromethane. Consequently, it is possible to estimate, using a single experiment, the possibility of using activated carbons for the storage of natural gas. On the other hand, the methane uptake can be also correlated to the volume of micropores, provided by the adsorption of N₂ at −196 °C and CO₂ at 0 °C, although the correlations is not as good. Only carbons slightly activated, with low surface area and microporosity below around 0.6 nm, do not adjust the above correlations because they adsorb more methane than the expected, the effect of chemical nature of the carbon surface being almost negligible.