Development of electrochemical cell with layered composite of the Gd-doped ceria/electronic conductor system for generation of H2–CO fuel through oxidation–reduction of CH4–CO2 mixed gases

This paper shows the recent results on the development of layered composite promoting two types of electrochemical reactions (oxidation and reduction) in one cell. This cell consisted of porous Ni–Gd-doped (GDC) ceria cathode/thin porous GDC electrolyte (50 μm)/porous SrRuO₃–GDC anode. The external electric current was flowed in this cell at the electric field strength of 1.25 and 6.25 V/cm. The mixed gases of CH₄ (30–70%) and CO₂ (70–30%) were fed at the rate of 50 ml/min to the cell heated at 400–800 °C under the electric field. In the cathode, CO₂ was reduced to CO (CO₂ + 2e^? → CO + O^2?) and the formed CO and O^2? ions were transported to the anode through the pores and surface and interior of grains of GDC film. On the other hand, CH₄ was oxidized in the anode to form CO and H₂ through the reaction with diffusing O^2? ions (CH₄ + O^2? → CO + 2H₂ + 2e^?). As a result, H₂–CO mixed fuel was produced from the CH₄–CO₂ mixed gases (CH₄ + CO₂ → 2H₂ + 2CO). This electrochemical reaction proceeded completely at 800 °C and no blockage of gases was measured for long time (>10 h). Only H₂–CO fuel was generated in the wide gas compositions of starting CH₄–CO₂ gases.     

Hydrogen formation from a real biogas using electrochemical cell with gadolinium-doped ceria porous electrolyte

The electrochemical cell consisting of a gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.95) porous electrolyte, Ni–GDC cathode and Ru–GDC anode was applied for the dry-reforming (CH₄+CO₂→2H₂+2CO) of a real biogas (CH₄ 60.0%, CO₂ 37.5%, N₂ 2.5%) produced from waste sweet potato. The composition of the supplied gas was adjusted to CH₄/CO₂=1/1 volume ratio. The supplied gas changed continuously into a H₂–CO mixed fuel with H₂/CO=1/0.949–1/1.312 vol ratios at 800 °C for 24 h under the applied voltage of 1–2 V. The yield of the mixed fuel was higher than 80%. This dry-reforming reaction was thermodynamically controlled at 800 °C. The application of external voltage assisted the reduction of NiO and the elimination of solid carbon deposited slightly in the cathode. The decrease of heating temperature to 700 °C reduced gradually the fraction of the H₂–CO fuel (61.3–18.6%) within 24 h. Because the Gibbs free energy change was calculated to be negative values at 700–600 °C, the above result at 700–600 °C originated from the gradual deposition of carbon over Ni catalyst through the competitive parallel reactions (CH₄→C+2H₂, 2CO→C+CO₂). The application of external voltage decreased the formation temperature of carbon by the disproportionation of CO gas. At 600 °C, the H₂–CO fuel based on the Faraday's law was produced continuously by the electrochemical reforming of the biogas.     

A DFT study of methanol oxidation on Co3O4

By means of spin polarized density functional theory with the GGA + U framework, the reaction mechanism of CH₃OH oxidation on the Co₃O₄ (110)-B and (111)-B surfaces has been investigated. Adsorption situation and a part of reaction cycle for CH₃OH oxidation are clarified. Our results indicated that: i) U value can affect the calculated energetic result significantly; ii) CH₃OH can adsorb with surface lattice oxygen atom (O_2f/O_3f) to form CoO bond directly, and the adsorption of CH₃OH and its decomposition products on (110)-B is more stable than on (111)-B, which means CH₃OH prefers Co^3 + better than Co^2 +; iii) on the (110)-B surface, CH₃OH can form CO₂, H₂O and adsorbed H atom. But on the (111)-B surface, CH₃OH can just form formaldehyde (CH₂O) and adsorbed H atom, this means oxidative capacity of (110)-B (Co^3 +) is higher than (111)-B (Co^2 +). The possible reasons corresponding to the high oxidative of (110)-B come from both Co^3 + and O_2f: Co^3 + tends to bind adsorbed species for further decomposition and O_2f tends to bind more hydrogenation atom involved in methanol due to its low-coordinates number compared to that of O_3f.     

The effects of enrichment by H2 on propagation speeds in adiabatic flat and cellular premixed flames of CH4 + O2 + CO2

Experimental studies of adiabatic flat and cellular premixed flames of (CH₄ + H₂) + (O₂ + CO₂) are presented. The hydrogen content in the fuel was varied from 0% to 35% and the oxygen content in the oxidizer was 31.55%. These mixtures could be formed when oxy-fuel combustion technology is combined with hydrogen enrichment. Non-stretched flames were stabilized at atmospheric pressure on a perforated plate burner. A heat flux method was used to determine propagation speeds under conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of methane + hydrogen + carbon dioxide + oxygen mixtures were found in satisfactory agreement with the detailed kinetic modeling employing the Konnov mechanism. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Visual and photographic observations of the flames were performed to quantify their cellular structure. The results obtained in the present work in (CH₄ + H₂) + O₂ + CO₂ mixtures are in good accordance with the previous observations for different fuels, CH₄, C₂H₆ and C₃H₈. The enrichment by hydrogen leads to: the increase of the laminar burning velocities; the increase of the number of cells observed; the decrease of the mean cell diameter. The flame acceleration due to cellularity was not affected by the hydrogen enrichment.     

Controllable synthesis of α-MoC1-x and β-Mo2C nanowires for highly selective CO2 reduction to CO

Transition metal carbides are attractive catalysts because of their similar properties to precious metals. Here, we report the controllable synthesis of α-MoC_1-x and β-Mo₂C nanowires as highly active and selective catalysts for CO₂ reduction to CO (CO₂ + H₂ → CO + H₂O, reverse water-gas shift reaction, RWGS). CO₂ conversion of > 60% together with nearly 100% CO selectivity was achieved at 600 °C, H₂:CO₂ molar ratio of 4:1, and space velocity of 36,000 mL g^− 1 h^− 1. A formate decomposition mechanism for the RWGS reaction was proposed based on the in-situ DRIFTS results.     

CO2 hydrogenation to methanol at pressures up to 950 bar

The methanol synthesis from CO₂ hydrogenation is of great interest because it offers a way to mitigate the anthropogenic CO₂ emissions and gives the opportunity to produce methanol from renewable and recyclable feedstock. Methanol is a key component in the chemical industry and can serve as fuel. In this work the high pressure approach of the transformation of CO₂ to methanol is investigated based on the energy balance for the production of 1 Mt methanol per year from air-captured CO₂ and hydrogen from water electrolysis. The energy efficiency is almost pressure independent and is comparable to literature values. The energy consumption for the compression of CO₂ and H₂ accounts only for 26% of the total energy consumption. Experimental investigations of the CO₂ hydrogenation at 950 bar show up to 15 times larger methanol space time yields (STY_methanol) compared to literature values where CO₂ was hydrogenated to methanol at 30 bar.     

Methane dry reformer by application of chemical looping combustion via Mn-based oxygen carrier for heat supplying and carbon dioxide providing

In this study, the production of H₂ utilizing chemical looping combustion (CLC) in a methane dry reformer assisted by H₂ perm-selective membranes in a CLC-DRM configuration has been investigated. CLC via employment of a Mn-based oxygen carrier generates large amounts of heat in addition to providing CO₂ as the raw material for the dry reforming (DR) reaction. The main advantage of the CLC-DRM configuration is the simultaneous capturing and consuming of CO₂ as a greenhouse gas for H₂ production.A steady state one dimensional heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC-DRM configuration. Simulation results show that CH₄ is completely consumed in the fuel reactor (FR) of the CLC-DRM and pure CO₂ is captured by condensation of H₂O. Also, CH₄ conversion and H₂ yield reach 73.46% and 1.459 respectively at the outlet of the DR side in the CLC-DRM. Additionally, 4562 kmol h⁻¹ H₂ is produced in the DR side of the CLC-DRM.Finally, results indicate that by increasing the FR feed temperature up to 880 K, CH₄ conversion and H₂ production are enhanced to 81.15% and 4790 kmol h⁻¹ respectively.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

A first-principles study on the role of hydrogen in early stage of graphene growth during the CH4 dissociation on Cu(1 1 1) and Ni(1 1 1) surfaces

The influence of hydrogen for CH₄ dissociation on Cu(1 1 1) and Ni(1 1 1) surfaces has been investigated by using the density functional theory. The two possible reactions, i.e. H-abstraction reaction (CH_x + H → CH_x−1 + H₂) and direct dehydrogenation reaction (CH_x + H → CH_x−1 + 2H), are studied. Our results show that H-abstraction reaction has higher energy barrier than direct dehydrogenation reaction on Cu(1 1 1), while for Ni(1 1 1), only the direct dehydrogenation reaction is observed. The microkinetic analysis supports that H-abstraction reaction is less competitive than the direct dehydrogenation reaction at broad coverage of H atom on Cu(1 1 1) surface. The major intermediate changes from CH to CH₃ on Cu(1 1 1) and Ni(1 1 1) with the increase of H₂ partial pressure. Furthermore, the behavior of free C atoms on both clean and H pre-adsorbed metal surfaces is discussed. The adsorbed H atom hinders the polymerization of the C atoms on Cu(1 1 1), resulting in sufficient time for C relaxed to the most stable site and further lead to a prefect graphene pattern formation, while H atom has little effect on such process for Ni(1 1 1).     

MLCT interaction in [Rh(II)2(CO3)4]4 −( x L)

Complexes of the type [Rh^II₂(CO₃)₄(H₂O)L]^n − with L = N-methylpyrazinium⁺ and 1-heptyl-4-(4-pyridinyl)pyridinium⁺ cations display intense long-wavelength (Rh(II) to L) MLCT absorptions. With L = H₂O, MLCT absorptions are not identified, but the photoreactivity of the complex in aqueous solution supports the assumption that (Rh(II) to CO₃^2 −) MLCT excited states are accessible. Upon irradiation with white light, Rh(II) is photooxidized while carbonate is reduced to CO. The efficiency of this photolysis is very low. However, the occurrence of this photoredox reaction is, nevertheless, of general interest with regard to the photochemical reduction of CO₂.     

Large area deposition of boron doped nano-crystalline diamond films at low temperatures using microwave plasma enhanced chemical vapour deposition with linear antenna delivery

We report on the preparation and characterisation of boron (B) doped nano-crystalline diamond (B-NCD) layers grown over large areas (up to 50 cm × 30 cm) and at low substrate temperatures (< 650 °C) using microwave plasma enhanced linear antenna chemical vapour deposition apparatus (MW-LA-PECVD). B-NCD layers were grown in H₂/CH₄/CO₂ and H₂/CH₄ gas mixtures with added trimethylboron (TMB). Layers with thicknesses of 150 nm to 1 μm have been prepared with B/C ratios up to 15000 ppm over a range of CO₂/CH₄ ratios to study the effect of oxygen (O) on the incorporation rate of B into the solid phase and the effect on the quality of the B-NCD with respect to sp³/sp² ratio. Experimental results show the reduction of boron acceptor concentration with increasing CO₂ concentration. Higher sp³/sp² ratios were measured by Raman spectroscopy with increasing TMB concentration in the gas phase without CO₂. Incorporation of high concentrations of B (up to 1.75 × 10²¹ cm³) in the solid is demonstrated as measured by neutron depth profiling, Hall effect and spectroscopic ellipsometry.     

Assembly of an imidazole templated indium-oxalate porous 3D framework with tcj/hc topology: Synthesis,structure and sorption property

A 3D In(III) metal organic framework {[(CH₃)₂NH₂][In₂(Ox)_3.5(Im)]∙H₂O∙DMF}_n (1) (Ox = oxalic acid, Im = imidazole) which is templated by imidazole molecules has been synthesized solvothermally. Compound 1, is an anionic framework with 1D open channels which are filled with (CH₃)₂NH₂⁺, DMF and water molecules. The network exhibits a 3,4-c binodal net with a rare tcj/hc topology. The total solvent accessible volume in the crystal is 43.2%. Sorption studies show that it can adsorb a maximum amount of 47 cm³ g^− 1 of CO₂ gas at 195 K while the uptake of N₂ and CH₄ is negligible.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Methanation of carbon dioxide over mesoporous Ni–Fe–Al2O3 catalysts prepared by a coprecipitation method: Effect of precipitation agent

Mesoporous nickel (30 wt%)–iron (5 wt%)–alumina (denoted as NiFeAl–X) catalysts were prepared by a coprecipitation method with a variation of precipitation agent (X = (NH₄)₂CO₃, Na₂CO₃, NH₄OH, and NaOH), and they were applied to the methane production from CO₂ and H₂. Metal particle size of reduced NiFeAl–X catalysts decreased in the order of NiFeAl–NaOH > NiFeAl–NH₄OH > NiFeAl–Na₂CO₃ > NiFeAl–(NH₄)₂CO₃. In the methanation of CO₂, yield for CH₄ increased in the order of NiFeAl–NaOH < NiFeAl–NH₄OH < NiFeAl–Na₂CO₃ < NiFeAl–(NH₄)₂CO₃. This indicates that the catalytic performance in the methanation of CO₂ was strongly influenced by the identity of precipitation agent.     

Self-assembly and magnetic behavior of 2-aldehyde-8-hydroxyquinolinate-based lanthanide complex

Self-assembly reaction of Ln(NO₃)_3.6H₂O, 2-aldehyde-8-hydroxyquinoline and histamine dihydrochloride affords two mononuclear complex [Ln(hma)(NO₃)₂(CH₃OH)]∙0.5C₄H₁₀ (Ln = Tb (1), Dy (2); Hhma = N-(2-(8-hydroxylquinolinyl)methane(2-(4-imidazolyl)ethylamine)). The structural analysis indicates that they are isomorphous where the Ln^3 + is ligated to one ligand, two nitrates and one methanol molecule. Variable temperature magnetic susceptibility studies reveal the presence of antiferromagnetic interactions in 2 and the dynamic measurement reveals that 2 displays single molecular magnet behavior below 10 K under an applied field of 2000 Oe.     

Semi-rigid N-para-ferrocenyl(benzoyl)amino-acid esters for biomaterials: synthesis and characterization of Fc-C6H4CONHCH(R)CO2Me where Fc = (η5-C5H5)Fe(η5-C5H4) and R=H,CH3,CH2CH(CH3)2,CH2C6H5 and the X-ray crystal structures of Fc-C6H4CO2Me and the l-alanine derivative Fc-C6H4CONHCH(CH3)CO2Me

A series of N-para-(ferrocenyl)benzoyl amino-acid esters, para-Fc(C₆H₄)CONHCH(R)CO₂CH₃ {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄); R = H, CH₃, CH₂CH(CH₃)₂, CH₂C₆H₅}, 3–6 have been prepared by coupling para-(ferrocenyl)benzoic acid to the amino-acid esters (gly, l-Ala, l-Leu, l-Phe) using the standard 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. The compounds were fully characterized by a range of spectroscopic techniques including FAB-MS. The X-ray crystal structures of the parent para-(ferrocenyl)benzoyl methyl ester, Fc-C₆H₄CO₂Me, 1 and a chiral derivative N-{para-(ferrocenyl)benzoyl}-l-alanine methyl ester, Fc-C₆H₄CONHCH(CH₃)CO₂Me, 4 have been determined.     

A highly thermal stable microporous lanthanide–organic framework for CO2 sorption and separation

A new lanthanide–organic framework formulated as TbL 1 (H₃L = 9-(4-carboxy-phenyl)-9H-carbazole-3,6-dicarboxylic acid), was synthesized under hydrothermal reaction condition. Single-crystal X-ray diffraction analysis shows that 1 crystallizes in a hexagonal P6₅ space group with three-dimensional network and microporous structure. The desolventized framework of 1 shows much higher uptake of CO₂ (43.7 cm³ g^− 1) than that of CH₄ (15.1 cm³ g^− 1) at 1 atm and 273 K, which makes it a potential candidate for CO₂/CH₄ separation.     

A polyhedron-based cobalt-organic framework for gas adsorption and separation

A cobalt-organic framework (1) consisted of close-packed polyhedral cages is isostructural to CPM-35-Ni. The activated sample (1a) can adsorb high H₂ uptake of 88.3 cm³ g^− 1 (0.79 wt.%) at 77 K and 1.0 bar. Remarkably, 1a shows high CO₂ adsorption capacity and good adsorption selectivity for CO₂ over CH₄ and N₂.     

High resolution electron energy loss spectroscopy of hydrogenated polycrystalline diamond: Assignment of peaks through modifications induced by isotopic exchange

In this work we unambiguously determine the origin of the different peaks which appear in the High Resolution Electron Energy Loss Spectrum (HREELS) of hydrogenated polycrystalline diamond films for an incident electron energy of 5 eV and loss energies extending to 700 meV. High quality diamond films deposited by hot filament chemical vapor deposition from various isotopic gas mixtures: ¹²CH₄ + H₂, ¹²CD₄ + D₂, ¹²CH₄ + D₂, ¹²CD₄ + D₂, ¹³CH₄ + H₂ were characterized. The different vibrational modes, fundamentals and overtones, were directly identified through the modifications of the HREEL spectra induced by the isotopic exchange of H by D and ¹²C by ¹³C Three types of peaks were identified: (1) pure C–C related peaks (a diamond optical phonon at ∼ 155 meV and its overtones at 300, 450 and 600 meV), (2) pure C–H related peaks (C–H bend at ∼ 150 meV and C–H stretch of sp³ carbon at 360 meV), (3) coupling of C–H and C–C peaks (510 meV peak due to coupling of the C–H stretch at 360 meV with either the C–C stretch or the C–H bend at ∼ 155 meV). The overtones at 300, 450 and 600 meV (associated with electron scattering at diamond optical phonons) indicate a well defined hydrogenated diamond surface since they are absent in the HREEL spectrum of low energy ion beam damaged diamond surface.     

Optimising H2 production from model biogas via combined steam reforming and CO shift reactions

H₂ production was studied through steam reforming of a clean model biogas in a fluidized-bed reactor followed by two stages of CO shift reactions (fixed-bed reactors). The steam reforming of biogas was performed over 11.5 wt.% Ni/Al₂O₃ and a molar CH₄/CO₂ ratio of 1.5 was employed as clean model biogas. Excess steam resulted in strong inhibition of carbon formation and an almost complete CH₄ (>98%) conversion was achieved.To optimise H₂ production, CO shift reactions were carried out at high (523–723 K) and low temperatures (423–523 K) using commercial catalysts, based on Cu/Fe/Cr and Cu/Zn, respectively. Increasing steam concentrations led to a lean CO, high H₂ product. The final product compositions following low temperature CO shift reaction (steam to dry gas ratio of 1.5 at 483 K) yielded H₂ at 68% and a CO concentration of 0.2% (equivalent to CO conversion of >99%).