The effect of active oxygen species in nano-ZnCr2O4 spinel oxides for methane catalytic combustion

The nano-ZnCr₂O₄ spinel oxides was synthesized by a ethylene glycol mediated solvothermal method. Catalytic combustion of methane test showed that an excellent activity over nano-ZnCr₂O₄ with T_10% = 300 °C and T_90% = 400 °C. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption-desorption measurements (BET) indicated that a uniform nano-ZnCr₂O₄ spinel oxides particles with the high surface area (96.2 m²g⁻¹) was successfully synthesized. Oxygen temperature programmed desorption (O₂-TPD) profile revealed there were two obvious desorption of oxygen species from nano-ZnCr₂O₄ in the range of 300–400 °C and 500–700 °C. It was clear that the desorption temperature range of the first oxygen species coincided with the methane catalytic combustion temperature. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Cr⁶⁺ was present in the lattice of ZnCr₂O₄ apart from Cr³⁺. High valence cations of chromium in crystal lattice probable caused the presence of interstitial oxygen species in the structure to maintain the electroneutrality. Additionally, Raman spectra proved that there is the interstitial oxygen species in the crystal lattice of ZnCr₂O₄. Therefore, the excellent catalytic activity for methane combustion was contributed to the flexible interstitial oxygen in the ZnCr₂O₄.     

Exploring the undrained cyclic behavior of methane-hydrate-bearing sediments using CFD–DEM

Based on the mechanical experimental results of methane hydrate (MH), a bond contact model considering the rate-dependency of MH is proposed. A CFD–DEM scheme considering fluid compressibility is used to simulate a series of undrained cyclic shear tests of numerical methane-hydrate-bearing sediment (MHBS) samples. The dynamic behavior, including stress–strain relationship, dynamic shear modulus, and damping ratio, is investigated. In addition, the force chains, contact fabric and averaged pure rotation rate (APR) are examined to investigate the relationships between micromechanical variables and macromechanical responses in the DEM MH samples. The effects of temperature, confining pressure and MH saturation are also analyzed. Due to the micro-structural strengthening by the MH bonds, no obvious change in microscopic quantities is observed, and the samples remain at the elastic stage under the applied low-shear stress level. When confining pressure and MH saturation increase, the dynamic elastic modulus increases, while the damping ratio decreases. An increasing temperature (leading to weakening of MH bonds) can lower the dynamic elastic modulus, but has almost no impact on the damping ratio. On the contrary, an increasing cyclic shear stress level lowers the damping ratio, but has almost no effect on the dynamic elastic modulus.     

Acidity Modification of ZSM-5 for Methane Conversion in Co-feeding Method with MTA Reaction

Acidity plays a vital role in methane conversion by co-feeding method, which is one of the best strategies to improve the utilization and gentle the reaction conditions of methane. In this work, Zn, Ni, Mo, La, Ga, Fe and Co-impregnated ZSM-5 zeolites have been prepared with the same substitutions to variate the acidities and tested in co-aromatization of methanol with methane. It is demonstrated that the new medium-strong acid sites formed by metal and strong acid sites are the key role to activate methane in co-reaction. Zn-modified ZSM-5 catalyst is preferred to exhibit the best methane conversion of 12%, whose aromatic selectivity increases from 27.2% to 52.2% compared with that of HZSM-5. Besides, the addition of methane further improves the production of high-valued aromatics compared with methanol to aromatics (MTA) reaction.     

Cobalt ferrite for direct cracking of methane to produce hydrogen and carbon nanostructure: Effect of temperature and methane flow rate

Cobalt ferrite (CoFe₂O₄) was used as a catalyst for direct methane cracking. The reaction was accomplished in a fixed bed reactor at normal atmospheric pressure, while gas flow rate (20–50 mL/min) and reaction temperature (800–900 °C) were varied. The fresh CoFe₂O₄ morphology is sponge-like particle with inverse spinel structure as revealed from SEM and XRD results. The methane conversions and hydrogen formation rate were increased with reaction temperature, while catalyst stability and induction period decreased. Increases of gas flow rate > 20 mL/min led to a decrease the overall catalytic activity of CoFe₂O₄ for methane cracking. The XRD results of spent catalysts revealed that CoFe alloy was the active phase of methane cracking. TGA analysis showed that the largest amount of deposited carbon was 70.46 % at (20 mL/min, 900 °C), where it was 34.40 % at (50 mL/min, 800 °C). The deposited carbon has the shape of spherical carbon nanostructures and/or nano sprouts as observed with SEM. Raman data confirmed the graphitization type of the deposited carbon.     

甲烷氧化菌利用甲烷生产聚羟基脂肪酸的研究进展

化学合成塑料主要来自于不可再生的化石能源,化学合成塑料的大量使用既消耗了大量能源物质,也带来了严重的环境问题。而生物合成的高分子化合物聚羟基脂肪酸,具有与合成塑料相似的物理性质,生产原料具有可再生性,同时在环境能快速降解,结构多样可以满足不同用途等多种优点,成为合成塑料最佳的替代品。甲烷氧化菌能以甲烷为唯一碳源和能源物质生长,并在细胞内合成大分子聚羟基脂肪酸。利用甲烷氧化菌转化甲烷合成聚羟基脂肪酸不仅可以大幅降低生产成本,同时也减少了温室气体的排放。本文就甲烷氧化菌合成聚羟基脂肪酸的生物代谢途径,甲烷为原料生产聚羟基脂肪酸的方法及优缺点等方面进行了分析。     

Experimental investigation on the dissociation conditions of methane hydrate in the presence of imidazolium-based ionic liquids

In this work, the performance of nine ionic liquids (ILs) as thermodynamic hydrate inhibitors is investigated. The dissociation temperature is determined for methane gas hydrates using a high pressure micro deferential scanning calorimeter between (3.6 and 11.2) MPa. All the aqueous IL solutions are studied at a mass fraction of 0.10. The performance of the two best ILs is further investigated at various concentrations. Electrical conductivity and pH of these aqueous IL solutions (0.10 mass fraction) are also measured. The enthalpy of gas hydrate dissociation is calculated by the Clausius–Clapeyron equation. It is found that the ILs shift the methane hydrate (liquid + vapour) equilibrium curve (HLVE) to lower temperature and higher pressure. Our results indicate 1-(2-hydroxyethyl) 3-methylimidazolium chloride is the best among the ILs studied as a thermodynamic hydrate inhibitor. A statistical analysis reveals there is a moderate correlation between electrical conductivity and the efficiency of the IL as a gas hydrate inhibitor. The average enthalpies of methane hydrate dissociation in the presence of these ILs are found to be in the range of (57.0 to 59.1) kJ ⋅ mol⁻¹. There is no significant difference between the dissociation enthalpy of methane hydrate either in the presence or in absence of ILs.     

Phase equilibrium measurements of (methane + benzene) and (methane + methylbenzene) at temperatures from (188 to 348) K and pressures to 13 MPa

New isothermal pTxy data are reported for (methane + benzene) and (methane + methylbenzene (toluene)) at pressures up to 13 MPa over the temperature range (188 to 313) K using a custom-built (vapor + liquid) equilibrium (VLE) apparatus. The aim of this work was to investigate literature data inconsistencies and to extend the measurements to lower temperatures. For (methane (1) + benzene (2)), measurements were made along six isotherms from (233 to 348) K at pressures to 9.6 MPa. At temperatures below 279 K there was evidence of a solid phase, and thus only vapor phase samples were analyzed at these temperatures. For the (methane (1) + methylbenzene (3)) system, measurements were made along seven isotherms from T = (188 to 313) K at pressures up to 13 MPa. Along the 198 K isotherm, a significant change in the data’s p,x slope was observed indicating (liquid + liquid) equilibria at higher pressures. The data were compared with literature data and with calculations made using the Peng–Robinson (PR) equation of state (EOS). For both binary systems our data agree with much of the literature data that also deviate from the EOS in a similar manner. However, the data of Elbishlawi and Spencer (1951) for both binary systems, which appear to have received an equal weighting to other data in the EOS development, are inconsistent with the results of our measurements and data from other literature sources.     

Effect of the order of Ni and Ce addition in SBA-15 on the activity in dry reforming of methane

Dry reforming of methane has been carried out on SBA-15 catalysts containing 5 wt% Ni and 6 wt% Ce. The effect of the order of Ni and Ce impregnation on the catalytic activity has been studied. Both metals were added using the “two-solvent” method that favors metal dispersion inside the pores. Characterizations by XRD (low and high angles), N₂ sorption, SEM and TEM of the materials after metal addition and calcination indicate good preservation of the porosities and high NiO and CeO₂ dispersion inside the porous channels. Reduction was carried out before the catalytic tests and followed by TPR measurements. The most active reduced catalyst was the Ni–Ce/SBA-15 sample prepared by impregnating cerium first, then nickel. All catalysts were highly active and selective towards H₂ and CO at atmospheric pressure. Full CH₄ conversion was obtained below 650 °C. The higher performances compared to those reported in the literature for mesoporous silica with supported Ni and Ce catalysts are discussed.     

Selective Oxidation of Methane into Methanol Under Mild Conditions

Selective oxidation of methane to methanol under mild conditions has been considered as a dream reaction but suffers from poor efficiency due to the strong C-H bond of methane and easy overoxidation of the methanol product. For overcoming these problems, a series of strategies has been developed for improving methanol productivity with oxidants of hydrogen peroxide and even a mixture of oxygen and hydrogen at mild temperatures. Significant achievements in these strategies using effective catalysts, such as supported metal nanoparticles, colloidal metal nanoparticles, and metal@zeolites are briefly concluded. Moreover, the current challenges, future perspectives for preparing active, selective, and stable catalysts, have been discussed. The zeolite fixed metal nanoparticle structure has been found to boost the reaction by benefiting the formation and enrichment of peroxide intermediates, which might guide the development of more efficient catalysts.