电场增强催化甲烷合成碳二烃催化剂影响研究

本研究提出了在常温、常压电场增强等离子体条件下甲烷直接转化合成碳二烃的洁净工艺 ,在不同的放电电压、放电功率、甲烷进料流量和不同的催化剂作用下 ,甲烷能够以不同的转化率和选择性转变为碳二烃。对影响甲烷转化率和碳二烃选择性的因素 :放电电压、放电功率、甲烷进料流量和催化剂进行了研究 ,对催化剂性能进行了比较 ,并探讨了反应机理。结果表明 ,适宜的工艺条件 :放电电压 2 0kV～ 4 0kV ;输入功率 :2 0W～ 4 0W ;合适的甲烷进料流量 :30mL/min～ 70mL/min。在该条件下 ,碳二烃的选择性可以达到 95 % ;催化剂对甲烷转化率的影响顺序为MnO2 /Al2 O3 >Ni/Al2 O3 >MoO3 /Al2 O3 >Ni/NaY >Pd/ZSM 5 >Ni/H4Mg2 Si3 O4>Ni/ZSM 5 >Co/ZSM 5 >无催化剂。     

On the chemical processing of hydrocarbon surfaces by fast oxygen ions

Solid methane (CH(4)), ethane (C(2)H(6)), and ethylene (C(2)H(4)) ices (thickness: 120 ± 40 nm; 10 K), as well as high-density polyethylene (HDPE: [C(2)H(4)](n)) films (thickness: 130 ± 20 nm; 10, 100, and 300 K), were irradiated with mono-energetic oxygen ions (Φ ~ 6 × 10(15) cm(-2)) of a kinetic energy of 5 keV to simulate the exposure of Solar System hydrocarbon ices and aerospace polymers to oxygen ions sourced from the solar wind and planetary magnetospheres. On-line Fourier-transform infrared spectroscopy (FTIR) was used to identify the following O(+) induced reaction pathways in the solid-state: (i) ethane formation from methane ice via recombination of methyl (CH(3)) radicals, (ii) ethane conversion back to methane via methylene (CH(2)) retro-insertion, (iii) ethane decomposing to acetylene via ethylene through successive hydrogen elimination steps, and (iv) ethylene conversion to acetylene via hydrogen elimination. No changes were observed in the irradiated PE samples via infrared spectroscopy. In addition, mass spectrometry detected small abundances of methanol (CH(3)OH) sublimed from the irradiated methane and ethane condensates during controlled heating. The detection of methanol suggests an implantation and neutralization of the oxygen ions within the surface where atomic oxygen (O) then undergoes insertion into a C-H bond of methane. Atomic hydrogen (H) recombination in forming molecular hydrogen and recombination of implanted oxygen atoms to molecular oxygen (O(2)) are also inferred to proceed at high cross-sections. A comparison of the reaction rates and product yields to those obtained from experiments involving 5 keV electrons, suggests that the chemical alteration of the hydrocarbon ice samples is driven primarily by electronic stopping interactions and to a lesser extent by nuclear interactions.     

Thermal stability of organopalladium compounds: Non-radical methyl elimination from [PdXMe(PEt3)2]

The thermolysis of the palladium complexes [PdX(Me){P(C₂H₅)₃}₂] (X = Br, I, CN; Me = CH₃, CD₃) in decalin or toluene under argon, in the temperature range 120–160°C, produces methane, ethane and ethylene, in ratios which vary with the temperature. Deuterium labelling shows that the methane is mainly formed through intramolecular abstraction of hydrogen from the phosphine ligands by the coordinated methyl group and not through homolytic fission of the PdMe bond. The thermal stability and the decomposition mechanisms of the organopalladium complexes are compared with those of the platinum analogues, which are remarkably more stable. At the higher temperatures, the thermal decomposition involves cleavage of the PEt bonds in the phosphine ligands, and this leads to the formation of ethane and ethylene. The rate of generation of methane from the PdMe moieties is increased by a factor of 10 by the presence of an excess of dioxygen. Deuterium isotopic labelling shows that the rate increase is accompanied by a change from an intramolecular to a radical mechanism involving the abstraction of hydrogen by the methyl groups.     

基于ReaxFF的甲烷无氧转化气相机理研究

With the rapid consumption of petrochemical resources and massive exploitation of shale gas, the use of natural gas instead of petroleum to produce chemical raw materials has attracted significant attention. While converting methane to chemicals, it has long seemed impossible to avoid its oxidation into O-containing species, followed by de-oxygenation. A breakthrough in the nonoxidative conversion of methane was reported by Guo et al. (Science 2014, 344, 616), who found that Fe©SiO₂ catalysts exhibited an outstanding performance in the conversion of methane to ethylene and aromatics. However, the reaction mechanism is still not clear owing to the complex experimental reaction conditions. One view of the reaction mechanism is that methane molecules are first activated on the Fe©SiC₂ active center to form methyl radicals, which then desorb into the gas phase to form the ethylene and aromatics. In this study, ReaxFF methods are applied to five model systems to study the gas-phase reaction mechanism under near-experimental conditions. For the pure gas-phase methyl radical system, the main simulation product is ethane after 10 ns simulation, which is produced by the combination of methyl radicals. Although a small amount of ethylene produced by C₂H₆ dehydrogenation can be detected, it is difficult to explain the high selectivity for ethylene in the experiment. When the methyl radicals are mixed with hydrogen and methane molecules, ethane remains the main product, together with some methane produced by the collision of hydrogen with methyl radicals, while ethylene is still difficult to produce. With the addition of hydrogen radicals to the methane atmosphere, methane activation can be enhanced by hydrogen radical collisions, which produce some methyl radicals and hydrogen molecules, but the methyl radicals eventually combine with the hydrogen species to produce methane molecules again. If some hydrogen molecules and methyl radicals are added to the CH₄/H∙ system, the activation of methane molecules by hydrogen radicals will be weakened. Hydrogen radicals are more likely to combine with themselves or with methyl radicals to form hydrogen and methane molecules, and the high selectivity for ethylene remains difficult to achieve. Thermal cracking of C₁₀H₁₂ at high temperature can produce hydrogen radicals and ethylene at the same time, which can partially explain the enhanced methane conversion and ethylene selectivity in the experiment of Hao et al. (ACS Catal. 2019, 9, 9045). Overall, the selective production of ethylene by nonoxidative conversion of methane over Fe©SiO₂ catalyst appears hard to achieve via a gas-phase mechanism. The catalyst surface may play a key role in the entire process of methane transformation.     

Decomposition of 1,1‐dimethyl‐1‐silacyclobutane on a tungsten filament—evidence of both ring C?C and ring Si?C bond cleavages

The decomposition of 1,1‐dimethyl‐1‐silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time‐of‐flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1‐dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si? CH₃ bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C? C bond and a ring Si? C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C? C bond is dominant over that of propene via an initial cleavage of a ring Si? C bond. When the collision‐free condition is voided, secondary reactions in the gas‐phase produce various methyl‐substituted 1,3‐disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3‐tetramethyl‐1,3‐disilacyclobutane originated from the dimerization of 1,1‐dimethylsilene. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient Sunlight-Driven Dehydrogenative Coupling of Methane to Ethane over a Zn(+) -Modified Zeolite

Sun bath: A Zn(+) -modified zeolite catalyst showing superior photocatalytic activity for the activation of a C?H bond converted methane into ethane and hydrogen upon irradiation of sunlight. Light at wavelengths shorter than 390?nm transferred electrons from the zeolite framework to the zinc centers.     

Vapor–liquid equilibrium of systems containing alcohols,water, carbon dioxide and hydrocarbons using SAFT

The statistical associating fluid theory (SAFT) equation of state is employed for the correlation and prediction of vapor–liquid equilibrium (VLE) of eighteen binary mixtures. These include water with methane, ethane, propane, butane, propylene, carbon dioxide, methanol, ethanol and ethylene glycol (EG), ethanol with ethane, propane, butane and propylene, methanol with methane, ethane and carbon dioxide and finally EG with methane and ethane. Moreover, vapor–liquid equilibrium for nine ternary systems was predicted. The systems are water/ethanol/alkane (ethane, propane, butane), water/ethanol/propylene, water/methanol/carbon dioxide, water/methanol/methane, water/methanol/ethane, water/EG/methane and water/EG/ethane. The results were found to be in satisfactory agreement with the experimental data except for the water/methanol/methane system for which the root mean square deviations for pressure were 60–68% when the methanol concentration in the liquid phase was 60 wt.%.     

甲醇直接气相羰基化反应动力学

甲醇直接气相羰基化研究 ,是在无任何促进剂下 ,ＣＯ与甲醇直接进行羰基化反应 ,这与目前公认的甲醇必须有碘化物作用下构成催化循环的间接羰化不同 ,在催化理论上有可能提出新的羰基化机理。彭峰等在甲醇直接气相羰基化方面 ,对具有高活性与选择性的非铑非卤素Ｍｏ Ｃ催化剂体系进行了系列研究 ,并取得了较好的实验结果[1～ 5] 。有碘甲烷参与的甲醇羰基化液相或者气相反应 ,大多数文献认为控制步骤是碘化物中Ｃ -Ｉ键的解离及ＣＯ的插入 ,羰基化反应是由一系列平行和连串反应组成的[6～ 8] 。催化剂类型不同得到的动力学参数也不相同 ,难…     

脉冲电晕等离子体作用下甲烷偶联反应的研究 Ⅱ.反应添加气的影响

脱氢偶联;脉冲电晕等离子体作用下甲烷偶联反应的研究 Ⅱ.反应添加气的影响     

Identifying Different Types of Catalysts for CO2 Reduction by Ethane through Dry Reforming and Oxidative Dehydrogenation

The recent shale gas boom combined with the requirement to reduce atmospheric CO₂ have created an opportunity for using both raw materials (shale gas and CO₂) in a single process. Shale gas is primarily made up of methane, but ethane comprises about 10 % and reserves are underutilized. Two routes have been investigated by combining ethane decomposition with CO₂ reduction to produce products of higher value. The first reaction is ethane dry reforming which produces synthesis gas (CO+H₂). The second route is oxidative dehydrogenation which produces ethylene using CO₂ as a soft oxidant. The results of this study indicate that the Pt/CeO₂ catalyst shows promise for the production of synthesis gas, while Mo₂C‐based materials preserve the C? C bond of ethane to produce ethylene. These findings are supported by density functional theory (DFT) calculations and X‐ray absorption near‐edge spectroscopy (XANES) characterization of the catalysts under in situ reaction conditions.     

Application of Si‐doped graphene as a metal‐free catalyst for decomposition of formic acid: A theoretical study

Using density functional theory calculations, the adsorption and catalytic decomposition of formic acid (HCOOH) over Si‐doped graphene are investigated. For the stable adsorption geometries of HCOOH over Si‐doped graphene, the electronic structure properties are analyzed by adsorption energy, density of states, and charge density difference. A comparison of the reaction pathways reveals that both dehydration and dehydrogenation of HCOOH can occur over Si‐doped graphene. The estimated reaction energies and the activation barriers suggest that for the dehydration of HCOOH on the Si‐doped graphene, the rate‐controlling step is H + OH → H₂O reaction. For the dehydrogenation of HCOOH, the rate‐determining step is the breaking of the C? H bond of the HCOO group to form the CO₂ molecule and the atomic H. Our results reveal that the low cost Si‐doped graphene can be used as an efficient nonmetal catalyst for O? H bond cleavage of HCOOH. © 2015 Wiley Periodicals, Inc.     

Preferential Activation of Primary C?H Bonds in the Reactions of Small Alkanes with the Diatomic MgO+. Cation

The C? H bond activation of small alkanes by the gaseous MgO^+. cation is probed by mass spectrometric means. In addition to H‐atom abstraction from methane, the MgO^+. cation reacts with ethane, propane, n‐ and iso‐butane through several pathways, which can all be assigned to the occurrence of initial C? H bond activations. Specifically, the formal C? C bond cleavages observed are assigned to C? H bond activation as the first step, followed by cleavage of a β‐C? C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO^+. for the attack of primary C? H bonds. This feature represents a notable distinction of the main‐group metal oxide MgO^+. from various transition‐metal oxide cations, which show a clear preference for the attack of secondary C? H bonds. The results of complementary theoretical calculations indicate that the C? H bond activation of larger alkanes by the MgO^+. cation is subject to pronounced kinetic control.     

Time‐dependent density functional theory study on the electronic excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in aqueous solution: 4AP and 4AP–(H2O)1,2 clusters

The time‐dependent density functional theory (TDDFT) method has been carried out to investigate the excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in hydrogen‐donating water solvent. The infrared spectra of the hydrogen‐bonded solute?solvent complexes in electronically excited state have been calculated using the TDDFT method. We have demonstrated that the intermolecular hydrogen bond C? O···H? O and N? H···O? H in the hydrogen‐bonded 4AP?(H₂O)₂ trimer are significantly strengthened in the electronically excited state by theoretically monitoring the changes of the bond lengths of hydrogen bonds and hydrogen‐bonding groups in different electronic states. The hydrogen bonds strengthening in the electronically excited state are confirmed because the calculated stretching vibrational modes of the hydrogen bonding C?O, amino N? H, and H? O groups are markedly red‐shifted upon photoexcitation. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electroniclly excited state of chromophores in hydrogen‐donating solvents exists in many other systems in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Palladium‐Catalyzed Reductive Insertion of Alcohols into Aryl Ether Bonds

Palladium on carbon catalyzes C?O bond cleavage of aryl ethers (diphenyl ether and cyclohexyl phenyl ether) by alcohols (R?OH) in H₂. The aromatic C?O bond is cleaved by reductive solvolysis, which is initiated by Pd‐catalyzed partial hydrogenation of one phenyl ring to form an enol ether. The enol ether reacts rapidly with alcohols to form a ketal, which generates 1‐cyclohexenyl?O?R by eliminating phenol or an alkanol. Subsequent hydrogenation leads to cyclohexyl?O?R.     

Hydride Ligands Make the Difference: Density Functional Study of the Mechanism of the Murai Reaction Catalyzed by [Ru(H)(2) (H(2) )(2) (PR(3) )(2) ] (R=cyclohexyl)

The catalytic cycle for the Murai reaction at room temperature between ethylene and acetophenone catalyzed by [Ru(H)(2) (H(2) )(2) (PMe(3) )(2) ] has been studied computationally at the B3PW91 level. The active species is the ruthenium dihydride complex [Ru(H)(2) (PMe(3) )(2) ]. Coordination of the ketone group to Ru induces very easy C?H bond cleavage. Coordination of ethylene after ketone de-coordination, followed by ethylene insertion into a Ru?H bond, creates the Ru?ethyl bond. Isomerization of the complex to a Ru(IV) intermediate creates the geometry adapted to C?C bond formation. Re-coordination of the ketone before the C?C coupling lowers the energy of the corresponding TS. The highest point on the potential energy surface (PES) is the TS for the isomerization to the Ru(IV) intermediate, which prepares the catalyst geometry for the C?C coupling step. Inclusion of dispersion corrections significantly lowers the height of the overall activation barrier. The actual bond cleavage and bond forming processes are associated to low activation barriers because of the presence of hydrogen atoms around the Ru center. They act as redox buffers through formation and breaking of H?H bonds in the coordination sphere. This flexibility allows optimal repartition of the various ligands according to the change in stereoelectronic demands along the catalytic cycle.     

Experimental investigation of fluidized-bed reactor performance for oxidative coupling of methane

Performance of the oxidative coupling of methane in fluidized-bed reactor was experimentally investigated using Mn-Na2WO4/SiO2,La2O3/CaO and La2O3-SrO/CaO catalysts.These catalysts were found to be stable,especially Mn-Na2WO4/SiO2 catalyst.The effect of sodium content of this catalyst was analyzed and the challenge of catalyst agglomeration was addressed using proper catalyst composition of 2%Mn2.2%Na2WO4/SiO2.For other two catalysts,the effect of Lanthanum-Strontium content was analyzed and 10%La2O 3-20%SrO/CaO catalyst was found to provide higher ethylene yield than La2O3/CaO catalyst.Furthermore,the effect of operating parameters such as temperature and methane to oxygen ratio were also reviewed.The highest ethylene and ethane (C2) yield was achieved with the lowest methane to oxygen ratio around 2.40.5% selectivity to ethylene and ethane and 41% methane conversion were achieved over La2O3-SrO/CaO catalyst while over Mn-Na2WO4 /SiO2 catalyst,40% and 48% were recorded,respectively.Moreover,the consecutive effects of nitrogen dilution,ethylene to ethane production ratio and other performance indicators on the down-stream process units were qualitatively discussed and Mn-Na2WO4/SiO2 catalyst showed a better performance in the reactor and process scale analysis.     

低碳烷烃与二氧化碳催化转化研究进展

页岩气革命为低碳经济发展提供了重要契机.在低碳烷烃(甲烷和乙烷)催化转化过程中,以二氧化碳作为氧化剂参与反应,通过C-H键的选择性活化可将页岩气转化为优质化工原料——合成气和乙烯,是一种低碳烷烃转化与二氧化碳资源化利用的工艺路线.本文总结了近年来甲烷干重整与乙烷和二氧化碳反应中与C-H键活化相关的研究进展,分析了甲烷干...     

Reactions of tetrakis(dimethylamino)ethylene with weak acids

Tetrakis(dimethylamino)ethylene reacts in methanol at 25° to give carbon-carbon bond cleavage, substitution of methoxyl for dimethylamino and addition of methanol to the double bond. The principal products are dimethylamine, dimethoxydimethylaminomethane and 1,1,2-trimethoxy-1,2-bis(dimethylamino)ethane. Minor products are methoxydimethylamino-N,N-dimethylacetamide, trimethylamine and dimethyl ether. An oxidation-reduction side reaction forms a very small amount of the radical cation of tetrakis(dimethylamino)ethylene. In the presence of sodium methoxide no carbon-carbon bond cleavage occurs and no radical cation is formed. When methanol is dissolved in tetrakis(dimethylamino)ethylene (methanol 1M), the principal products are 1,1,2-trimethoxy-1,2-bis(dimethylamino)ethane and dimethylamine with small amounts of tris(dimethylamino)methoxyethylene and 1,2-bis(dimethyl amino)-1,2-dimethoxyethylene. Tetrakis(dimethylamino)ethylene and water give dimethylamine and dimethylformamide.     

Fine structure at the carbon 1s K edge in vapours of simple hydrocarbons

Electron yield spectra in the range of 280 ? ?ω ? 300 eV which basically resemble the absorption spectra, have been measured for gaseous methane, ethane, ethylene, benzene and acetylene using synchrotron radiation. The spectra being fairly simple compared to the valence shell absorption are characterized by weak maxima for energies below the ionization threshold for C 1s for methane and ethane whereas additional strong resonances are observed in the spectra from molecules containing π-electrons. The nature of these excitations is discussed on the basis of their term values using information from XPS-measurements.     

Boron Group Ions Direct Conversion of Carbon and Methane into Ethylene in DFT Study

In this study, density functional theory calculations reveal how boron group ions M^+(M = B, Al, Ga, In, and Tl) directly convert carbon and methane into ethylene at room temperature. M^+ reacts with the carbon atom to form the cation MC^+. Then, the reaction of MC^+ with methane leads to the cleavage of metal-carbon bond and the formation of CH2CH2 through C-C coupling, with the ion M^+ serving as a leaving group. The cycle then begins again. The mechanism of C/CH4 system catalyzed by five ion types is investigated herein, and the reasons for the different reactivity of five ion types are determined. The moderate strength of the Al^+-C bond results in Al^+ being the only appropriate catalyst of M^+(M?=?B, Al, Ga, In, and Tl) that can catalyze methane and carbon into ethylene.