甲烷氧化细菌催化二氧化碳生物合成甲醇的研究

甲烷氧化细菌中包含的甲烷单加氧酶(MMO)、甲醇脱氢酶(ADH)、甲醛脱氢酶(FaldDH)、甲酸脱氢酶(FateDH)经过一系列反应能够把甲烷深度氧化生成二氧化碳，并生成一定的能量物质．把二氧化碳还原为甲醇是一个需要能量的过程，目前还没有已知的有机体在温和条件下完成这一反应．研究发现，甲基弯菌Methylosi-nus trichosporium IMV 3011可以催化二氧化碳生物转化生成甲醇．在休眠的悬浮细胞中充人二氧化碳后，反应一段时间在反应液中检测到了甲醇．二氧化碳转化成甲醇是一个需要能量推动的反应，为了补充反应所消耗的能量．反应一段时间后需要用甲烷进行再生，以恢复细胞中的还原当量NADH．我们进行了反应再生的交替连续批式反应，甲醇积累量能够维持在一个比较稳定的水平．理论上，反应不会增加温室效应，这是一个有效的、环境友好的、可恢复的反应过程．     

甲烷生物催化氧化制甲醇:固定化细胞催化剂的制备及其催化性能的研究

研究了利用无机载体（活性炭、氧化铝、分子筛等）吸附法和天然藻胶（海藻酸钙等）包埋法制备的固定化甲烷氧化细菌的催化性能及其在生物反应器中的反应，结果表明，在进行甲烷制甲醇的反应中、活性炭吸附制备的固定化细胞的操作稳定性最好，但其初始酶活性与休止游离细胞相比损失了６０％￣８０％，海藻酸钙包埋的固定化细胞初始酶活性高（与游离细胞相比，可保持５５％￣９０％的酶活性），但反应中甲醇累积速度很低，而双重介质（     

二氧化碳存在下甲烷氧化细菌催化甲烷生物合成甲醇

 在甲烷单加氧酶和脱氢酶系的作用下,甲烷氧化细菌Methylosinus trichosporium IMV 3011可以把甲烷氧化成二氧化碳. 在反应体系中充入一定比例的二氧化碳后,检测到了甲醇的积累. 混合气中CO2,CH4,O2和N2的体积比为2∶1∶1∶1时甲醇的积累量达到最大. 在超滤膜反应器中进行了连续反应,利用反应混合气产生的压力将生成的甲醇从反应体系中分离. 连续反应198 h后甲醇的积累量没有明显下降.     

温和条件下催化甲烷氧化制甲醇研究进展

甲烷是燃料或化工生产中最丰富的碳基能源之一,将甲烷转化为液体或固体化学原料将成为全球能源供应的转折点.目前,许多催化此类反应的工作已有大量研究和报道.在这些反应中,甲烷选择性氧化制甲醇被认为是天然气就地价值化的一条有前途的途径.这使得甲烷低温选择性氧化制甲醇技术的发展变得非常迫切,本文综述了CH₄的活化和催化转化,指出了针对特定反应的催化剂的发展趋势.讨论了理想条件下甲烷氧化制取甲烷的反应研究以及Au–Pd合金类、ZSM-5类、MOFs类、单原子类等催化剂对甲烷氧化过程的影响及其催化转化机理.最后,对温和条件下催化甲烷氧化制甲醇催化剂未来发展提出了展望和挑战.     

NOx催化的甲烷气相氧化反应

 考察了没有固体催化剂时NOx对甲烷气相氧化的催化作用，并用原位红外光谱研究了CH4－O2－NOx体系随温度的变化．实验结果表明，NOx对甲烷气相氧化有很高的催化活性．在20％CH4－10％O2体系中加入0．05％～0．2％的NO后，反应温度可降低200～300℃，在650～700℃下反应时，CH4转化率和CO选择性可分别达到38％和90％，产物中的n（H2）／n（CO）比为0．4～0．7．反应产物中可观察到有甲醛、甲醇和乙烯等，通过改变反应条件可以控制各组分的相对浓度．     

甲醇驱动的环氧丙烷连续生物合成

采用甲醇蒸气作为碳源对甲基弯菌IMV 3011进行驯化培养,然后逐渐增加液态甲醇的浓度使其适应,得到了能耐受甲醇(φ(MeOH)=1%)的甲基弯菌IMV 3011.对甲基弯菌IMV 3011进行甲烷-甲醇共培养可得到大量具有甲烷单加氧酶(MMO)活性的细胞.研究了添加甲醇对甲基弯菌IMV 3011生长和MMO活性的影响,发现甲醇能够促进甲基弯菌IMV3011的生长.在批式反应器中,添加甲醇能够提高甲基弯菌IMV 3011的催化环氧化能力,说明甲醇可以作为电子供体通过再生辅酶NADH驱动环氧丙烷合成.考察了在膜反应器中用细胞悬浮液连续合成环氧丙烷的可行性.结果表明,通过192 h连续抽提产物环氧丙烷,避免了其对环氧化反应的抑制,流出液中环氧丙烷的浓度仍保持在1.35 mmol/L左右.     

大肠杆菌异源表达pmoB及催化甲烷氧化生成甲醇的研究

颗粒甲烷单加氧酶(pMMO)是甲烷氧化菌中催化甲烷氧化生成甲醇的一种酶.Methylococcus capsulatus IMV3021的pMMO活性位点是pmoB亚基,该亚基是一种可溶性蛋白.我们研究将pmoB亚基进行异源表达及生物催化活性的验证.当培养基中烟酰胺腺嘌呤二核苷酸(NADH)浓度为5 mmol/L时,可以观察到异源表达pmoB亚基具有催化甲烷氧化成甲醇活性,生成甲醇浓度为1.04 mmol/L.研究pMMO活性对于开发能直接将甲烷转化成甲醇的新型、环保催化剂有非常重要意义.     

含钒杂多酸催化发烟硫酸中甲烷液相部分氧化反应

 以H5PV2Mo10O40 为催化剂,在发烟硫酸中进行了甲烷液相部分氧化,考察了催化剂用量、反应温度、反应时间和发烟硫酸浓度等工艺条件对反应收率的影响. 甲烷在反应中首先转化为硫酸甲酯,硫酸甲酯随后水解为甲醇. 对于甲烷液相部分氧化反应,发烟硫酸中游离的SO3是非常重要的影响因素. 在工艺条件为催化剂用量7.0 mmol, 反应温度473 K, 反应压力3.5 MPa, 反应时间3 h和发烟硫酸中SO3含量50%时,甲烷转化率可达48.5%, 目的产物甲醇收率为41.5%.     

甲烷直接催化氧化制备甲醇近期研究进展北大核心CSCD

甲烷合成甲醇的方法包括间接法和直接催化氧化(DMTM)法,但是间接法对设备要求高,且甲烷转化率与甲醇选择性均不理想,DMTM法可通过一步反应高选择性制备甲醇,有巨大的应用潜力。对于甲烷DMTM法合成甲醇,均相催化体系通常需要特殊反应介质与贵金属催化剂相结合,虽然反应效率高,但对反应设备有腐蚀性,产物不易分离,应用前景差。液相-异相催化一般使用H_(2)O_(2)作为氧化剂,Au、Pd、Fe和Cu等金属元素作为催化剂主要活性组分,·OH是主要的氧化活性物,可在低温下实现甲烷的活化氧化。因此,异相催化体系是目前研究的主流。气相-异相催化主要使用O_(2)和N_(2)O为氧化剂,前者氧化性更强,后者对于产品选择性更好,此外,厌氧体系中H_(2)O也可直接作为氧供体,常用Cu、Fe、Rh等元素作为催化剂。沸石分子筛是使用最广泛的载体,金属氧化物、金属有机骨架化合物(MOFs)和石墨烯也均有涉及,多金属协同催化已经取得了很好的效果。本文主要总结与概述了热催化甲烷直接催化氧化制备甲醇的近年相关研究,并对今后的研究方向做出了展望。     

甲烷直接氧化制甲醇研究进展概述

目前,天然气转化为高附加值化工产品的应用越来越受到人们关注.甲烷作为天然气的主要成分,其转化和应用是天然气化工领域的重要研究方向.而甲烷直接氧化制甲醇长久以来一直是研究重点.甲烷直接氧化制甲醇与传统的甲烷二步法间接转化相比,有节能和工艺简化的突出特点.然而,甲醇直接氧化制甲醇过程所面临的主要问题有：(1)甲烷分子的活化能很高,需要苛刻的操作条件才能活化参与反应;(2)反应进行的程度难以控制,生成的甲醇会进一步被氧化生成较多副产物,大大降低甲醇收率.因此,高效活化甲烷分子和抑制甲醇深度氧化是促进该过程工业化的重要研究内容.本文主要论述了非均相、气相均相和液相体系中甲烷直接氧化制甲醇的研究进展.在甲烷非均相氧化过程中,采用过渡金属氧化物作为催化剂在高温条件下催化甲烷部分氧化反应,其中,钼系和铁系催化剂的研究最为广泛.研究表明, MoO3可作为催化剂的主要活性组分,尤以 MoO3/Ga2O3催化剂性能最好,得到甲醇收率最高.在铁系催化剂中, Fe-ZSM-5 催化反应的甲醇选择性和收率都相对较高;但是每次反应后催化剂都需要重新活化,这种间歇性操作会增加成本,不利于工业化应用.总之,甲烷的非均相氧化过程存在易形成金属聚集体、催化剂选择性低以及甲醇收率低(5%)等问题,需要深入系统地研究解决.然而,与非均相氧化过程相比,操作较为简单的甲烷气相均相氧化作为目前最有工业前景的过程受到越来越多关注.在此过程中,影响反应的主要因素有反应器、反应条件(反应压力、反应温度和反应时间等)以及添加的介质等.反应器的特殊设计需要考虑的方面有反应产物的分离与转移、反应热的移除以有效提高甲烷的转化率,比如膜反应器对物质的分离作用.反应压力对反应过程的影响较为复杂.基于动力学因素,提高反应压力可以较大幅度地增加甲醇收率,同时最佳反应温度降低,但是,当压力高于8.0 MPa时,设备成本消耗大幅增加.另外,研究表明,进料中加入 NOx作为添加介质可以提高甲烷转化率和甲醇选择性,同时降低初始反应温度.与前两个氧化体系相比,液相均匀氧化过程能够获得较高的甲烷转化率与甲醇选择性.但是液相体系中强腐蚀性介质的使用增加了设备成本,阻碍了该过程工业化的应用进程.因此,促进液相体系工业化的关键就是开发绿色高效的催化剂.     

Methanol permeability in sulfonated poly(etheretherketone) membranes: A comparison with Nafion membranes

Partially sulfonated poly(etheretherketone) (SPEEK) samples were prepared by modification of corresponding poly(etheretherketone) (PEEK) with concentrated sulfuric acid. Membranes cast from these materials were evaluated as polymer electrolytes for direct methanol fuel cells (DMFCs). SPEEK membranes were characterized by ¹H NMR, FT-IR and TGA. The transverse proton conductivities increased from 4.1 to 9.3 × 10⁻³ S/cm with the increase of the degree of sulfonation (DS) from 0.59 to 0.93. These values were comparable with that of Nafion 117 membrane (1.0 × 10⁻² S/cm) measured under the same condition. Nearly one order magnitude difference between transverse conductivity and longitudinal conductivity was found. The methanol permeabilities of the SPEEK membranes were all lower than that of Nafion 117 membrane. The effects of temperature and methanol concentration on the methanol permeability were also studied. In addition, the selectivities of the SPEEK membranes for protons and methanol were all higher than that of Nafion 117 membrane.     

甲醇在Ru(0001)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Ru15为模拟表面,对甲醇在理想的Ru(0001)面三种吸附位置(top,fcc,hcp)的吸附模型进行了几何构型优化,能量计算,Mu lliken布局分析以及振动频率计算,结果表明顶位为最有利的吸附位.这些变化与实验观察到的甲醇在过渡金属表面解离的结果相一致.同时通过对吸附过程的分析推测其可能的解离途径.     

First-Principles Microkinetic Study of Methanol Synthesis on Cu(221) and ZnCu(221) Surfaces

First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO₂ on Cu(221) and CuZn(221) surfaces. It is found that regardless of surface structure, the carbon consumption rate follows the order:CO hydrogenation > CO/CO₂ hydrogenation > CO₂ hydrogenation. The superior CO hydrogenation activity mainly arises from the lower barriers of elementary reactions than CO₂ hydrogenation. Compared to Cu(221), the introduction of Zn greatly lowers the activity of methanol synthesis, in particularly for CO hydrogenation. For a mixed CO/CO₂ hydrogenation, CO acts as the carbon source on Cu(221) while both CO and CO₂ contribute to carbon conversion on CuZn(221). The degree of rate control studies show that the key steps that determine the reaction activity of CO/CO₂ hydrogenation are HCO and HCOO hydrogenation on Cu(221), instead of HCOOH hydrogenation on CuZn(221). The present work highlights the effect of the Zn doping and feed gas composition on methanol synthesis.     

Synthesis of Ga-incorporated SAPO-34s (GaAPSO-34) and their catalytic performance on methanol conversion

This study has been focused on the synthesis of GaAPSO-34s substituted gallium for aluminum in order to improve the acidic property in SAPO-34 crystal. As the result, GaAPSO-34s with various Al/Ga ratios (Al/Ga=∞, 40, 20, 10, 5, and 0) were successfully synthesized. These were characterized by XRD, SEM, ICP, TG-DTA, MAS-NMR, and BET surface areas. The crystallinity identified from the intensity of XRD peak (for angles of 22.5° and 9.7°) and the particle size observed from SEM photographs decreased with an increase in the Ga content incorporated into the SAPO-34 framework. On the other hand, decrease in the acid sites in crystal as a target in this study was confirmed in the Ga-incorporated samples. In particular, a surprising result was that the selectivity to ethylene on methanol conversion increased in catalyst with Al/Ga=20 compared with pure SAPO-34 catalyst. However, in spite of the decreases in acid sites and particle size in catalyst with much more Ga content, the selectivity to ethylene was not enhanced, rather the methane which related to catalytic deactivation increased in GaAPSO-34 catalysts. This is ascribed to collapses of framework of SAPO-34 with an increase in Ga content.     

甲醇-水、乙醇-水体系聚集态的共振散射光谱

自从Ｐａｓｔｅｒｎａｃｋ[1,2]使用普通荧光分光光度计建立共振光散射(ＲＬＳ)技术以来,人们用该技术建立了十分灵敏的蛋白质和核酸的分析方法[3,5]。同时该技术在研究化合物在溶液中的聚集态方面也有了较为广泛的应用,一般认为分子聚集体的形成是引起ＲＬＳ增强的主要原因[6]。已知甲醇、乙醇与水互溶形成均匀的溶液体系,那么在这些溶液体系中是否也存在某种形式的分子聚集体呢?为此本文研究了不同浓度的甲醇水溶液和乙醇水溶液的ＲＬＳ光谱。1　实验部分1 1　试剂和仪器甲醇(上海建鑫化工试剂厂,分析纯,含量%≥99 5);乙醇(安徽特酒总…     

Preparation of iron molybdate catalysts for methanol to formaldehyde oxidation based on ammonium molybdoferrate(II) precursor

It was demonstrated that iron molybdate catalysts for methanol oxidation can be prepared using Fe(II) as a precursor instead of Fe(III). This would allow for reduction of acidity of preparation solutions as well as elimination of Fe(III) oxide impurities which are detrimental for the process selectivity. The system containing Fe(II) and Mo(VI) species in aqueous solution was investigated using UV–Vis spectroscopy. It was demonstrated that three types of chemical reactions occur in the Fe(II)–Mo(VI) system: (i) formation of complexes between Fe(II) and molybdate(VI) ions, (ii) inner sphere oxidation of coordinated Fe(II) by Mo(VI) and (iii) decomposition of the Fe–Mo complexes to form scarcely soluble Fe(III) molybdate, Mo(VI) hydrous trioxide and molybdenum blue. Solid molybdoferrate(II) prepared by interaction of Fe(II) and Mo(VI) in solution was characterized by EDXA, TGA, DTA and XRD and a scheme of its thermal evolution proposed. The iron molybdate catalyst prepared from Fe(II) precursor was tested in methanol-to-formaldehyde oxidation in a continuous flow fixed-bed reactor to show similar activity and selectivity to the conventional catalyst prepared with the use of Fe(III).     

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.     

MEA with double-layered catalyst cathode to mitigate methanol crossover in DMFC

Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm⁻², which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure.     

多孔聚乙酰苯胺纳米纤维载铂催化剂对甲醇的电催化氧化

采用简单的化学氧化聚合法制备了新型多孔结构的聚乙酰苯胺纳米纤维(np-PAANI), 并以此为载体在络合剂的存在下合成了Pt纳米微粒修饰的np-PAANI复合物膜电极C/np-PAANI/Pt. 样品的形貌和结构通过扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)进行了表征. 在0.5 mol·L-1 CH3OH+0.5 mol·L-1 H2SO4混合溶液中考察了C/np-PAANI/Pt催化剂对甲醇的电催化氧化性能. 结果表明, 以np-PAANI负载的Pt催化剂对甲醇的电催化氧化活性和稳定性都比普通PAANI结构及石墨粉负载的Pt催化剂好很多.     

Electrocatalytic activities of binary and ternary composite electrodes of Pd, nanocarbon and Ni for electro-oxidation of methanol in alkaline medium

Films of binary and ternary composites of Pd, nanocarbon (C), and Ni are obtained on glassy carbon electrodes and investigated as electrocatalysts for methanol oxidation (MOR) in alkaline medium. Results show that among the electrocatalysts investigated, the apparent electrocatalytic activity of the Pd-0.5%C electrode is the greatest and that it decreases with increasing percentage of C in the composite. The Pd-0.5%C composite electrode has approximately two times higher activity than that of Pd electrode for MOR under similar experimental conditions. Introduction of Ni (1–2%) into the active Pd-0.5%C catalyst somewhat declines the apparent electrocatalytic activity of the electrode. The onset potential for MOR is observed to be the greatest negative at the Pd-0.5%C composite electrode, which gets shifted towards noble side by 80–100 mV with addition of Ni (1–2%).