Decorating Single-Atom Catalysts with CO for Efficient Methane Conversion

Direct methane conversion has advantages such as low energy consumption,less processes,and being more economical.However,it is difficult to activate methane at room temperature due to the high dissociation energy of C-H bonds of methane.Additionally,the target products,such as methanol,acetic acid,and other oxygenates,are prone to overoxidation,resulting in the generation of CO_(2).Therefore,the design of catalysts with high activity and selectivity is important.

A review of the direct oxidation of methane to methanol

This article briefly reviewed the advances in the process of the direct oxidation of methane to methanol （DMTM） with both heterogeneous and homogeneous oxidation. Attention was paid to the conversion of methane by the heterogeneous oxidation process with various transition metal ox‐ides. The most widely studied catalysts are based on molybdenum and iron. For the homogeneous gas phase oxidation, several process control parameters were discussed. Reactor design has the most crucial role in determining its commercialization. Compared to the above two systems, aque‐ous homogenous oxidation is an efficient route to get a higher yield of methanol. However, the cor‐rosive medium in this method and its serious environmental pollution hinder its widespread use. The key challenge to the industrial application is to find a green medium and highly efficient cata‐lysts.

Biosynthesis of poly-3-hydroxybutyrate with a high molecular weight by methanotroph from methane and methanol

Poly-3-hydroxybutyrate （PHB） can be produced by various species of bacteria. Among the possible carbon sources, both methane and methanol could be a suitable substrate for the production of PHB. Methane is cheap and plentiful not only as natural gas, but also as biogas. Methanol can also maintain methanotrophic activity in some conditions. The methanotrophic strain Methylosinus trichosporium IMV3011 can accumulate PHB with methane and methanol in a brief nonsterile process. Liquid methanol （0.1%） was added to improve the oxidization of methane. The studies were carried out using shake flasks. Cultivation was performed in two stages： a continuous growth phase and a PHB accumulation phase under the conditions short of essential nutrients （ammonium, nitrate, phosphorus, copper, iron （Ⅲ）, magnesium or ethylenediamine tetraacetate （EDTA）） in batch culture. It was found that the most suitable growth time for the cell is 144 h. Then an optimized culture condition for second stage was determined, in which the PHB concentration could be much increased to 0.6 g/L. In order to increase PHB content, citric acid was added as an inhibitor of tricarboxylic acid cycle （TCA）. It was found that citric acid is favorable for the PHB accumulation, and the PHB yield was increased to 40% （w/w） from the initial yield of 12% （w/w） after nutrient deficiency cultivation. The PHB produced is of very high quality with molecular weight up to 1.5 × 10^6Da.

Methane formation route in the conversion of methanol to hydrocarbons

The influence factors and paths of methane formation during methanol to hydrocarbons （MTH） reaction were studied experimentally and thermodynamically. The fixed-bed reaction results show that the formation of methane was favored by not only high temperature, but also high feed velocity, low pressure, as well as weak acid sites dominated on deactivated catalyst. The thermodynamic analysis results indicate that methane would be formed via the decomposition reactions of methanol and DME, and the hydrogenolysis reactions of methanol and DME. The decomposition reactions are thermal chemistry processes and easily occurred at high temperature. However, they are influenced by catalyst and reaction conditions through DME intermediate. By contrast, the hydrogenolysis reactions belong to catalytic processes. Parallel experiments suggest that, in real MTH reactions, the hydrogenolysis reactions should be mainly enabled by surface active H atom which might come from hydrogen transfer reactions such as aromatization. But H2 will be involved if the catalyst has active components like NiO.

Application of in-plasma catalysis and post-plasma catalysis for methane partial oxidation to methanol over a Fe_2O_3-CuO/γ-Al_2O_3 catalyst

Methane partial oxidation to methanol （MPOM） using dielectric barrier discharge over a Fe2O3-CuO/γ-Al2O3 catalyst was performed.The multicomponent catalyst was combined with plasma in two different configurations,i.e.,in-plasma catalysis （IPC） and post-plasma catalysis （PPC）.It was found that the catalytic performance of the catalysts for MPOM was strongly dependent on the hybrid configuration.A better synergistic performance of plasma and catalysis was achieved in the IPC configuration,but the catalysts packed in the discharge zone showed lower stability than those connected to the discharge zone in sequence.Active species,such as ozone,atomic oxygen and methyl radicals,were produced from the plasma-catalysis process,and made a major contribution to methanol synthesis.These active species were identified by the means of in situ optical emission spectra,ozone measurement and FT-IR spectra.It was confirmed that the amount of active species in the IPC system was greater than that in the PPC system.The results of TG,XRD,and N2 adsorption-desorption revealed that carbon deposition on the spent catalyst surface was responsible for the catalyst deactivation in the IPC configuration.

Direct partial oxidation of methane to methanol:Reaction zones and role of catalyst location

Direct partial oxidation of methane to methanol was investigated in a specially designed reactor. Methanol yield of about 7%-8% was obtained in gas phase partial oxidation. It was proposed that the reactor could be divided into three reaction zones, namely pre-reaction zone, fierce reaction zone, and post-reaction zone, when the temperature was high enough to initiate a reaction. The oxidation of methane proceeded and was completed mostly in the fierce reaction zone. When the reactant mixture entered the post-reaction zone, only a small amount of produced methanol would bring about secondary reactions, because molecular oxygen had been exhausted in the fierce reaction zone. A catalyst, if necessary, should be placed either in the pre-reaction zone, to initiate a partial oxidation reaction at a lower temperature, or in the fierce reaction zone to control the homogeneous free radical reaction.

Photoelectrocatalytic oxidation of methane into methanol and formic acid over ZnO/graphene/polyaniline catalyst

ZnO/graphene/polyaniline(PANI) composite is synthesized and used for photoelectrocatalytic oxidation of methane under simulated sun light illumination with ambient conditions. The photoelectrochemical(PEC) performance of pure ZnO, ZnO/graphene, ZnO/PANI, and ZnO/graphene/PANI photoanodes is investigated by cyclic voltammetry(CV),chronoamerometry(J–t) and electrochemical impedance spectroscopy(EIS). The yields of methane oxidation products,mainly methanol(CH_3OH) and formic acid(HCOOH), catalysed by the synthesized ZnO/graphene/PANI composite are 2.76 and 3.20 times those of pure ZnO, respectively. The mechanism of the photoelectrocatalytic process converting methane into methanol and formic acid is proposed on the basis of the experimental results. The enhanced photoelectrocatalytic activity of the ZnO/graphene/PANI composite can be attributed to the fact that graphene can efficiently transfer photo-generated electrons from the inner region to the surface reaction to form free radicals due to its superior electrical conductivity as an inter-media layer. Meanwhile, the introduction of PANI promotes solar energy harvesting by extending the visible light absorption and enhances charge separation efficiency due to its conducting polymer characteristics.In addition, the PANI can create a favorable π-conjunction structure together with graphene layers, which can achieve a more effective charge separation. This research demonstrates that the fabricated ZnO/graphene/PANI composite promises to implement the visible-light photoelectrocatalytic methane oxidation.

Recent Progress in Direct Partial Oxidation of Methane to Methanol

The direct conversion of methane to methanol has attracted a great deal ofattention for nearly a century since it was first found possible in 1902, and it is still achallenging task. This review article describes recent advancements in the direct partial oxidationof methane to methanol. The history of direct oxidation of methane and the difficulties encounteredin the partial oxidation of methane to methanol are briefly summarized. Recently reporteddevelopments in gas-phase homogeneous oxidation, heterogeneous catalytic oxidation and liquid phasehomogeneous catalytic oxidation of methane are reviewed.

Direct conversion of methane to methanol by electrochemical methods

A convenient method for methane(CH_(4))direct conversion to methanol(CH_(3)OH)is of great significance to use methane-rich resources,especially clathrates and stranded shale gas resources located in remote regions.Theoretically,the activation of CH_(4) and the selectivity to the CH_(3)OH product are challenging due to the extreme stability of CH_(4) and relatively high reactivity of CH_(3)OH.The state-of-the-art‘methane reforming-methanol synthesis’process adopts a two-step strategy to avoid the further reaction of CH_(3)OH under the harsh conditions required for CH_(4) activation.In the electrochemical field,researchers are trying to develop conversion pathways under mild conditions.They have found suitable catalysts to activate the C–H bonds in methane with the help of external charge and have designed the electrode reactions to continuously generate certain active oxygen species.These active oxygen species attack the activated methane and convert it to CH_(3)OH,with the benefit of avoiding over-oxidation of CH_(3)OH,and thus obtain a high conversion efficiency of CH_(4) to CH_(3)OH.This mini-review focuses on the advantages and challenges of electrochemical conversion of CH4 to CH_(3)OH,especially the strategies for supplying electro-generated active oxygen species in-situ to react with the activated methane.

Selective Oxidation of Methane to Methanol Using Molecular Oxygen on MoOx/(LaCoO3+Co3O4)Catalysts

Comparatively high CH3OH selectivity (60.0%) and yield (6.7%) were obtained on MoOx/(LaCoO3+Co3O4) catalysts in selective oxidation of methane to methanol using molecular oxygen as oxidant. The interaction between MoOx and La-Co-oxide modified the molecular structure of molybdenum oxide and the ratio of O7O ' on the catalyst surface, which controlled the catalytic performance of MoOx/(LaCoO3+Co3O4) catalysts.

Effect of Dimethyl Ether Co-feed on Catalytic Performance of Methane Dehydroaromatization over Mo/HZSM-5 Catalyst

The effect of dimethyl ether (DME) co-feed on the catalytic performance of methane dehy-droaromatization (MDA) over 6Mo/HZSM-5 catalyst was investigated as a function of DME concentration under reaction conditions of T=1023 K, p=101 kPa and SV=1500 ml/(g·h). A high benzene yield was obtained and the stability of the catalyst was improved by adding 1.5%DME to the CH4 feed. The C6H6 yield was as high as ca. 10% even after reaction for 6 h. The stability of the catalyst was further improved when DME concentration in the co-feed gas was increased to an appropriate value. TGA and TPO results of the used 6Mo/HZSM-5 catalyst showed that the amount of coke on the used catalyst was reduced and the chemical nature of the coke was changed. When 1.5%DME was added to the CH4 feed, the coke formed on the catalyst could be burned off more easily than that when only CH4 was used as reactant. It is supposed that the oxygen in DME may play a role in preventing the coke burnt off at lower temperature from transforming into the coke burnt off at higher temperature, which results in the improvement of the stability of the catalyst.

Formation of Methane and Ethylene in Methanol Conversion over HZSM-5 Catalyst

Primary formation of methane and secondary formation of ethylene in methanol conversion are evidenced by temperature-programmed-surface- reaction of adsorbed methanol on HZSM-5 catalyst.A reaction mechanism accounts for the observed results is described.

Photocatalytic oxidation of methane to methanol over zinc titanate supported silver catalysts

The direct activation of methane under mild condition to achieve highly selective of oxygenates is a challenging project.In this study,a well dispersed silver supported ZnTiO_(3) catalyst was prepared to achieve selective preparation of methanol from methane and water under mild condition.X-ray diffraction,transmission electron microscopy and X-ray photoelectron spectroscopy characterizations demonstrate that silver species are uniformly dispersed on ZnTiO_(3) surface in the form of metallic silver nanoparticles.The photoelectric characterizations reveal that the addition of silver species enhances light absorption and promotes charge separation of the catalysts.Under the reaction conditions of 50℃and 3 MPa,the methanol is obtained as the only liquid product over the designed Ag/ZnTiO_(3) catalyst under light irradiation.In this photocatalytic process,the holes generated by ZnTiO_(3) activate water to produce intermediate·OH,which further reacts with methane to synthesize methanol.The silver species as co-catalysts extend the light absorption range of ZnTiO_(3) as well as promote charge separation.

Direct oxidation of methane to oxygenates over heteropolyanions

Partial oxidation of methane to formaldehyde and methanol was studied at atmospheric pressure in the temperature range of 700-750 °C using heteropolycompound catalysts （NH4）6HSiMo11FeO40, （NH4）4PMo11FeO39, and H4PMo11VO40, which were prepared and characterized by various analysis techniques such as infrared, visible UV, XRD and DTA. O2 or N2O was used as the oxidizing agent, and the principal products of the reaction were CH3OH, CH2O, CO, CO2, and water. The conversion and the selectivity of products depend strongly on the reaction temperature, the nature of oxidizing agent, and the composition of catalyst.

Minimizing carbon deposition in plasma-induced methane coupling with structured hydrogenation catalysts

The effect of temperature and hydrogen addition on undesired carbonaceous deposit formation during methane coupling was studied in DBD-plasma catalytic-wall reactors with Pd/Al2 O3, using electrical power to drive the reaction.Experiments with thin catalyst layers allowed comparison of the performance of empty reactors and catalytic wall reactors without significantly influencing the plasma properties.The product distribution varies strongly in the temperature window between 25 and 200℃Minimal formation of deposits is found at an optimal temperature around 75℃ in the catalytic-wall reactors.The selectivity to deposits was c.a.10% with only 9 mg of catalyst loading instead of 45% in the blank reactor,while decreasing methane conversion only mildly.Co-feeding H2 to an empty reactor causes a similar decrease in selectivity to deposits,but in this case methane conversion also decreased significantly.Suppression of deposits formation in the catalytic-wall reactor at 75℃ is due to catalytic hydrogenation of mainly acetylene to ethylene.In the empty reactor,H2 co-feed decreases conversion but does not change the product distribution.The catalytic-wall reactors can be regenerated with H2-plasma at room temperature,which produces more added-value hydrocarbons.

甲醇/甲烷层流扩散火焰碳烟生成的模拟研究

为充分了解甲醇对碳烟生成的影响,构建甲醇/甲烷混合燃烧机理,耦合Moss-Brookes碳烟模型,建立甲醇/甲烷层流火焰燃烧模型,在保证碳流量一定的情况下,研究甲醇掺混比(质量分数)分别为0、10%、20%、30%、40%这5种掺混比的甲醇/甲烷层流扩散火焰的碳烟生成特性。研究结果表明:甲醇的添加会导致火焰的起燃位置降低,从而导致碳烟在火焰更低的位置生成。火焰中碳烟体积分数随甲醇掺混比的增加先增加后减小,在30%甲醇掺混比下火焰的碳烟体积分数峰值达到最大值,碳烟体积分数为4.12×10^(-8)。甲醇掺混比升高会使O和OH的峰值升高,但在30%甲醇掺混时,峰值会在轴向位置发生向上偏移,导致30%甲醇掺混时碳烟体积分数为最大值。

顶空气相色谱-质谱联用法同时测定食品用洗涤剂中的三种成分

建立了顶空气相色谱-质谱联用仪(HS-GC-MS)同时测定食品用洗涤中的甲醛、甲醇和1,4-二噁烷的方法。方法对顶空进样的影响因素进行了单因素方差分析和正交试验,确定最优试验条件;选择强极性色谱柱SH-Rtx-Wax(30 m×0.32 mm×0.25μm)进行分离;采用选择离子扫描(SIM)模式和外标法定量分析。实验结果表明,甲醛、甲醇和1,4-二噁烷分别在8~200,8~200和2~50μg/mL范围内线性关系良好,检出限(LOD)在0.10~0.60μg/mL,定量限(LOQ)在0.29~1.78μg/mL;对实际样品添加低、中、高三个水平进行加标回收和精密度试验,加标回收率在84.0%~101.9%,相对标准偏差(RSD)在0.5%~3.7%。该方法操作简单、灵敏度高、重复性好,能够满足食品用洗涤剂中甲醛、甲醇、1,4-二噁烷同时测定的要求,同时也为我国食品用洗涤剂相关安全指标提供技术依据和参考。

焦炉煤气催化制甲烷和低碳醇研究进展

冶金煤气是冶金工业产生的气体,处理不当会造成严重的碳排放及空气污染,使钢铁行业碳中和面临巨大挑战。冶金煤气,尤其是其中的焦炉煤气,不仅可作为燃料使用,而且其富含的碳、氢元素是重要的化工资源。通过钢化联产工艺制造化学品实现钢铁行业减排,有望解决温室气体排放、资源浪费、能源消耗和空气污染等环境和能源问题。在催化固碳工艺中,以焦炉煤气催化制甲烷和低碳醇等产品因其过程具有工艺路线短、操作可行性强等优点最受关注。首先介绍了焦炉煤气催化制甲烷和甲醇的工艺条件及反应机理,并介绍助剂和载体等因素对催化剂抗积炭能力及稳定性的影响。其次,强调了构建具有高活性和稳定性的双活性中心对焦炉煤气制其他低碳醇催化剂设计的重要性,并阐述了前体结构和助剂等因素对改性费托合成催化剂和改性甲醇催化剂的影响机制。从反应条件看,甲烷化需较高温度,而制甲醇需较高压力;从工艺复杂程度看,甲烷化最简单,而制甲酸最复杂;从耗氢量看,甲酸不需消耗氢气,而甲烷化耗氢量最大。钢化联产应在综合考虑各种现实因素及产品经济效益的基础上,因地制宜开展催化降碳,不断推动钢化联产技术的创新及清洁能源技术的发展。

Facet-dependent catalytic activity of CeO_(2) toward methanol synthesis from methane

The relationship between CeO_(2) morphology(nano rods,NR;nano cubes,NC;nano octahedra,NO) and methanol synthesis from methane at low reaction temperature was studied by using density functional theory(DFT) and experiments.CeO_(2)(110) displays the lowest energy barriers among CeO_(2)(100),CeO_(2)(111) and CeO_(2)(110) surfaces due to the strongest hybridization between O 2p orbital of OH and Ce4f orbital.As a result,CeO_(2)-NR has the highest methanol yield(1.52 μmol/gcat) compared with CeO_(2)-NC(0.60 μmol/gcat)and CeO_(2)-NO(0.66 μmol/gcat) at 453 K and 101325 Pa.These results show that methanol synthesis from methane at low reaction temperature on CeO_(2)is a morphology sensitive reaction.

氢基绿色工业产品和传统工艺的全生命周期碳足迹对比评估

“双碳”目标下,氢能正成为促进我国可再生能源规模化消纳与实现能源电力系统低碳/零碳排放的重要技术路径之一。在甲烷、甲醇和钢铁等氢能应用的工业过程中,以可再生能源制备的绿色氢气替代传统的工业副产氢可降低工业产品的全生命周期碳足迹,但基于绿氢的新型工业生产方式相对于传统生产方式的降碳能力有待量化评估。文章通过构建基于全生命周期评价理论的碳中和能力量化评估模型,从产业生态学的角度,以绿色甲烷、绿色甲醇和绿色钢铁为对象,根据各产品的生产流程进行碳足迹评价,并将结果与基于传统化石能源生产的产品碳足迹进行对比。结果表明,与传统工艺相比,基于绿氢的新能源系统生产的绿色甲烷、绿色甲醇和绿色钢铁都具有不同程度的碳减排能力。本研究量化评估了基于绿氢的新型工业生产方式在大规模氢能应用时代的深度脱碳能力,为绿氢应用系统接入碳交易市场提供了量化评估指标。