The Catalytic Hydrogenation of Carbon Monoxide. The Formation of C1 Hydrocarbons

Abstract

Both the production of methane and methanol from CO and H₂ are important processes in chemical technology. They also have a distinguished history as the formation of methane was first reported by Sabatier and Senderens [1] in 1902. Methanol synthesis from CO and H₂ was first reported by Patart [2] in 1921, and in 1923 Badische Anilin and Soda Fabrik (BASF) announced the synthesis of CH₃OH to the exclusion of other products [3]. The catalytic reactions that produced these two molecules, however, have been subjected to molecular scale studies only recently. We shall review here what is known about the kinetics and mechanisms of these reactions, about the catalytically active surface, and the nature of the surface chemical bond of CO, H₂, and the reaction intermediates.     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

Methane steam reforming over Ni/Ce–ZrO2 catalyst: Influences of Ce–ZrO2 support on reactivity, resistance toward carbon formation, and intrinsic reaction kinetics

Ni/Ce–ZrO₂ showed good methane steam reforming performance in term of stability toward the deactivation by carbon deposition. It was first observed that the catalyst with Ce/Zr ratio of 3/1 showed the best activity among Ni/Ce–ZrO₂ samples with the Ce/Zr ratios of 1/0, 1/1, 1/3, and 3/1. Temperature-programmed oxidation (TPO) experiments indicated the excellent resistance toward carbon formation for this catalyst, compared to conventional Ni/Al₂O₃; the requirement of inlet H₂O/CH₄ to operate without the formation of carbon species is much lower. These benefits are related to the high oxygen storage capacity (OSC) of Ce–ZrO₂. During the steam reforming process, in addition to the reactions on Ni surface (*), the redox reactions between the gaseous components present in the system and the lattice oxygen (O_x) on Ce–ZrO₂ surface also take place. Among these reactions, the redox reactions between the high carbon formation potential compounds (CH₄, CH_x-*n and CO) and the lattice oxygen (O_x) can prevent the formation of carbon species from the methane decomposition and Boudard reactions, even at low inlet H₂O/CH₄ ratio (1.0/1.0).

Regarding the intrinsic kinetic studies in the present work, the reaction order in methane over Ni/Ce–ZrO₂ was observed to be approximately 1.0 in all conditions. The dependence of steam on the rate was non-monotonic, whereas addition of oxygen as an autothermal reforming promoted the rate but reduced CO and H₂ production selectivities. The addition of a small amount of hydrogen increased the conversion of methane, however, this positive effect became less pronounced and the methane conversion was eventually inhibited when high hydrogen concentration was added. Ni/Ce–ZrO₂ showed significantly stronger negative impact of hydrogen than Ni/Al₂O₃. The redox mechanism on ceria proposed by Otsuka et al. [K. Otsuka, T. Ushiyama, I. Yamanaka, Chem. Lett. (1993) 1517; K. Otsuka, M. Hatano, A. Morikawa, J. Catal. 79 (1983) 493; K. Otsuka, M. Hatano, A. Morikawa, Inorg. Chim. Acta 109 (1985) 193] can explain this high inhibition.     

REACTOR-MEMBRANE PERMEATOR CASCADE FOR ENHANCED PRODUCTION AND RECOVERY OF H2 AND CO2 FROM THE CATALYTIC METHANE-STEAM REFORMING REACTION

The catalytic reforming of methane by steam is an important industrial process that produces H₂, CO and CO₂, thus chemically transforming natural gas, coal gas and light hydrocarbon feedstocks to synthesis gas or hydrogen fuel. Methane-steam reforming may consist of a number of reactions depending on the reforming catalyst, operating conditions and feedstock composition, The typical industrially desirable reactions are the reverse of methanation (CH₄ + H₂O = CO + 3H₂) and the water-gas shift (CO + H₂O = CO₂ + H₂). Both reactions are equilibrium limited and the composition of the mixture that exits the reformer is in accordance with the one calculated thermodynarmically. Removal of reaction products at the reactor exit by means of selective membrane permeation can offer improved CH₄ conversions and CO₂ and H₂ yields, assuming the subsequent utilization of the reject streams by a second methane-steam reformer. We numerically investigated the feasibility of a system of two tubular methane-steam reformers, in series with an intermediate permselective polyimide membrane permeator, as means of improving the overall CH₄ conversion and the H₂, CO₂ yields over conventional methane-steam reforming equilibrium reaction-separation schemes that are currently in industrial practice. The unique feature of the permselective polyimide separator is the simultaneous removal of H₂ and CO₂ versus CH₄ and CO from the reformed streams. The utilized 6FDA-3,3', 5,5'-TMB aromatic polyimide was reportedly characterized [10] and found to exhibit superior permselective properties compared with other polyimides of the same or different dianhydride sequence. Conversion and yield of the designed reactor-membrane permeator reforming system can be maximized by optimizing the permselective properties of the membrane material and the design variables of the reactors and the permeator. Product recovery and purity in the permeate stream need to be compromised to overall enhance methane conversion and product yield. The operating variables that were varied to investigate their effect on the magnitude of conversion and yield included the inlet pressure of the first reformer, the temperature of both reformers, and the permeator dimensionless Pe' number (variation of the first two variables results to a drastic change in the composition of the reformed stream that enters into the permeator). The numerical results show that the new reformer-membrane permeator cascade process can be more effective (it can offer increased CH₄ conversions and H₂, CO₂ yields) than conventional equilibrium methane-steam reforming reaction-separation processes currently in practice.     

Roles of CO2 and H2O as oxidants in the plasma reforming of aliphatic hydrocarbons

Roles of CO₂ and H₂O as oxidants are discussed based on the data on the substrate conversions and the product distributions in the nonthermal plasma reforming of aliphatic hydrocarbons such as methane, propane, and neopentane from 303 K to 433 K. Only small effects of initial concentrations of hydrocarbons and types of oxidants are observed on hydrocarbon conversions, and the initial chemical interaction between hydrocarbons and the oxidants unlikely occurs. CO₂ and H₂O have shown the comparable oxidation powers in the hydrocarbon reforming. Two molar excess of CO₂ or H₂O to methane is required to oxidize methane carbon atoms to CO and CO₂, and larger amounts of CO₂ or H₂O for propane and neopentane. The different natures of CO₂ and H₂O are reflected in the synthesis gas composition as in the ordinary catalytic reforming processes at higher temperatures: higher H₂ yields and higher H₂ to CO ratios on addition of H₂O.     

Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy

In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH₄/O₂/He (2/1/45) gas mixture with adsorbed CO species over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over H₂ reduced and working state Rh/SiO₂ catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO₂ catalyst. CO₂ is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts is via the reforming reactions of CH₄ with CO₂ and H₂O. The effect of space velocity on the partial oxidation of methane over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO₂ formation during the partial oxidation of methane to synthesis gas over Rh/SiO₂ and Ru/γ-Al₂O₃ catalysts.     

Catalytic synthesis of methanethiol from hydrogen sulfide and carbon monoxide over vanadium-based catalysts

The direct synthesis of methanethiol, CH₃SH, from CO and H₂S was investigated using sulfided vanadium catalysts based on TiO₂ and Al₂O₃. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO₂ and H₂S by COS hydrolysis.

Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H₂S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al₂O₃. The TiO₂, V₂O₅/TiO₂ and V₂O₅/Al₂O₃ catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V₂O₅ in the sulfur exchange reactions taking place in the reaction network of H₂S and CO.     

褐煤热解-气化-制油系统的CO2减排策略

褐煤热解-气化-制油系统是现代煤化工发展的一个重要研究内容。来自系统多个单元产生的CH₄和CO₂如果发生重整反应,将重整得到H₂/CO比值较高的合成气添加到制油流程中,可实现更多的C被固定到产品中而减少CO₂的直接排放量。对CH₄-CO₂和CH₄-H₂O两种重整反应方式、来自煤热解和费托合成两股甲烷气和典型的干粉气化和水煤浆气化两种流程进行了组合研究。分析结果显示,来自热解和费托合成的甲烷重整后不足以提供调节合成气H₂/CO比例所需的氢气,水煤气变换反应对于褐煤制油系统来说是必需的。从C转化成油的角度来看,采用干粉气化和CH₄-H₂O重整的方案是较好的选择。     

Partial oxidation of CH4 and C2H6 over noble metalcoated monoliths

The direct partial oxidation of hydrocarbons offers promising alternatives to chemical synthesis. By replacing endothermic processes such as steam reforming and steam cracking, fast and exothermic oxidation reactions should require much smaller and simpler reactors. However, direct oxidation reactions are much more difficult to manage because of potential heat release in total oxidation and hazardous because of the possibility of homogeneous reactions which are nonselective and can produce flames and explosions. We describe experiments in which monolith catalysts are used for partial oxidation of CH₄ and C₂H₆ to produce synthesis gas or alkenes by direct oxidation at or above atmospheric pressure in pure O₂ in nearly adiabatic reactors operating at 1000°C with very high flowrates (space velocities of 10⁶h⁻¹ and residence times of 10⁻³ s). With methane oxidation we obtain over 90% selectivities to synthesis gas (a 2:1 H₂:CO mixture) with> 90% conversion of the methane and complete conversion of O₂ on Rh coated ceramic monoliths with contact times of 10⁻³ s. With Pt catalysts under the same conditions, the H₂ selectivity drops to 70%; while with Pd, the catalyst rapidly forms carbon. This process appears to be primarily a surface reaction in which CH4 pyrolyzes on the hot Rh surface and the H atoms dimerize and the carbon is oxidized to CO. A model has been constructed which accurately predicts the conversions and selectivities and the variations between Rh and Pt. With higher alkanes, synthesis gas is produced on Rh with comparable selectivities and conversions on metal-coated monoliths. However, with Pt we observe up to 70% selectivity to alkenes with 80% conversion of alkanes at adiabatic temperatures near 1000°C with approximately 5 ms contact times. These results can be explained as occurring by predominantly surface reactions in which the alkane adsorbs to form the alkyl by H abstraction with adsorbed O atoms. Then the adsorbed alkyls undergo primarily β-elimination reactions on Pt to produce alkenes. These products are therefore far from thermodynamic equilibrium at these very short contact times, even though the temperatures are very high. The use of very short contact times and high temperatures promises to provide new routes to production of partial oxidation products with very small adiabatic reactors and thus opens up new types of reactions and reactors for chemical synthesis.     

A comparison of H2 addition to 3 ms partial oxidation reactions

We compare the effects of adding large amounts of H₂ to 3 ms partial oxidation reactions, ethane to ethylene, propane to olefins, and methane and ammonia to HCN. It is found that H₂ can be safely added at the 2/1 H₂/O₂ stoichiometry in the presence of these fuels without any homogeneous reactions, flames, or explosions. For all of these systems the addition of H₂ increases the selectivities to the desired products while strongly decreasing CO and CO₂. Addition of H₂ forces water formation near the front face of the catalyst which consumes O₂ and allows dehydrogenation processes to dominate.     

La2NiO4 tubular membrane reactor for conversion of methane to syngas

La₂NiO₄ tubular membranes of relative density over 92% were used to separate oxygen from air and facilitate the partial oxidation of methane to H₂ and CO at 900 °C. When methane was fed into a tube of inner surface area 5.11 cm² at a rate of 10.5 ml/min, methane throughput conversion was 89%, CO selectivity 96%, H₂/CO ratio 1.5, and the equivalent oxygen flux was 6.8 ml/min. The surface of the La₂NiO₄ membrane exposed to CH₄ decomposed into La₂O₃ and Ni, while the surface in contact with air remained almost unchanged. It is suggested that the conversion of methane in the membrane reactor involves the reforming of methane by the H₂O and CO₂ catalyzed by nickel.     

CO and CO2 hydrogenation study on supported cobalt Fischer–Tropsch synthesis catalysts

The conversion of CO/H₂, CO₂/H₂ and (CO+CO₂)/H₂ mixtures using cobalt catalysts under typical Fischer–Tropsch synthesis conditions has been carried out. The results show that in the presence of CO, CO₂ hydrogenation is slow. For the cases of only CO or only CO₂ hydrogenation, similar catalytic activities were obtained but the selectivities were very different. For CO hydrogenation, normal Fischer–Tropsch synthesis product distributions were observed with an of about 0.80; in contrast, the CO₂ hydrogenation products contained about 70% or more of methane. Thus, CO₂ and CO hydrogenation appears to follow different reaction pathways. The catalyst deactivates more rapidly for the conversion of CO than for CO₂ even though the H₂O/H₂ ratio is at least two times larger for the conversion of CO₂. Since the catalyst ages more slowly in the presence of the higher H₂O/H₂ conditions, it is concluded that water alone does not account for the deactivation and that there is a deactivation pathway that involves the assistance of CO.     

Partial oxidation of methane to synthesis gas over iridium–nickel bimetallic catalysts

Partial oxidation of methane to synthesis gas was carried out using supported iridium–nickel bimetallic catalysts, in order to reduce loading levels of iridium and nickel, and to avoid carbon deposition on nickel-based catalysts by adding iridium. The performance of supported iridium–nickel bimetallic catalysts in synthesis gas formation depended strongly upon the support materials. La₂O₃ gave the best performance among the support materials tested. Ir(0.25 wt%)–Ni(0.5 wt%)/La₂O₃ afforded 36% conversion of methane (CH₄/O₂=5) to give CO and H₂ with the selectivities of above 90% at 800°C, and those at 600°C were 25.3% conversion of methane and CO and H₂ selectivities of about 80%, respectively. Reduced monometallic Ir(0.25 wt%)/La₂O₃ and Ni(0.5 wt%)/La₂O₃ catalysts did not produce synthesis gas at 600°C. A higher conversion of methane was obtained by synergistic effects. The product concentrations of CO, H₂, and CO₂, and CH₄ conversion were maintained in high values, even increasing the space velocity of feed gas over Ir–Ni/La₂O₃ catalyst, indicating that rapid reaction takes place. As a by-product, a small amount of carbon deposition was observed, but carbon formation decreased with increasing the space velocity. On the other hand, with reduced monometallic Ni(10 wt%)/La₂O₃ catalyst, yield of synthesis gas and carbon decreased with increasing the space velocity.     

CO, H2 or C3H8 assisted catalytic combustion of methane over supported LaMnO3 monoliths

The effect of the addition of a second fuel such as CO, C₃H₈ or H₂ on the catalytic combustion of methane was investigated over ceramic monoliths coated with LaMnO₃/La-γAl₂O₃ catalyst. Results of autothermal ignition of different binary fuel mixtures characterised by the same overall heating value show that the presence of a more reactive compound reduces the minimum pre-heating temperature necessary to burn methane. The effect is more pronounced for the addition of CO and very similar for C₃H₈ and H₂. Order of reactivity of the different fuels established in isothermal activity measurements was: CO>H₂≥C₃H₈>CH₄. Under autothermal conditions, nearly complete methane conversion is obtained with catalyst temperatures around 800 °C mainly through heterogeneous reactions, with about 60–70 ppm of unburned CH₄ when pure methane or CO/CH₄ mixtures are used. For H₂/CH₄ and C₃H₈/CH₄ mixtures, emissions of unburned methane are lower, probably due to the proceeding of CH₄ homogeneous oxidation promoted by H and OH radicals generated by propane and hydrogen pyrolysis at such relatively high temperatures.

Finally, a steady state multiplicity is found by decreasing the pre-heating temperature from the ignited state. This occurrence can be successfully employed to pilot the catalytic ignition of methane at temperatures close to compressor discharge or easily achieved in regenerative burners.     

Kinetics of the water–gas shift reaction on Pt catalysts supported on alumina and ceria

We report the kinetic parameters for the water–gas shift (WGS) reaction on Pt catalysts supported on ceria and alumina under fuel reformer conditions for fuel cell applications (6.8% CO, 8.5% CO₂, 22% H₂O, 37.3% H₂, and 25.4% Ar) at a total pressure of 1 atm and in the temperature range of 180–345 °C. When ceria was used as a support, the turnover rate (TOR) for WGS was 30 times that on alumina supported Pt catalysts. The overall WGS reaction rate (r) on Pt/alumina catalysts as a function of the forward rate (r_f) was found to be: r = r_f(1 − β), where r_f = k_f[CO]^0.1[H₂O]^1.0[CO₂]^−0.1[H₂]^−0.5, k_f is the forward rate constant, β = ([CO₂][H₂])/(K_eq[CO][H₂O]) is the approach to equilibrium, and K_eq is the equilibrium constant for the WGS reaction. The negative apparent reaction orders indicate inhibition of the forward rate by CO₂ and H₂. The surface is saturated with CO on Pt under reaction conditions as confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The small positive apparent reaction order for CO, in concert with the negative order for H₂ and the high CO coverage is explained by a decrease in the heat of adsorption as the CO coverage increases. Kinetic models based on redox-type mechanisms can explain the observed reaction kinetics and can qualitatively predict the changes in CO coverage observed in the DRIFTS study.     

Oxidative conversion of methane to syngas over NiO/MgO solid solution supported on low surface area catalyst carrier

Influence of time-on-stream (0.5–15 h), CH₄/O₂ ratio in feed (1.8–8.0), space velocity (6000–510,000 cm³ g⁻¹ h⁻¹), catalyst particle size (22–70 mesh), and catalyst dilution by inert solid particles (diluent/catalyst weight ratio=4) on the performance at different temperatures (600–900°C) of the NiO/MgO solid solution deposited on SA-5205 [which is a low surface area macroporous silica-alumina catalyst carrier] in the oxidative conversion of methane to syngas (a mixture of CO and H₂) has been investigated. The dependence of conversion and selectivity on the space velocity is strongly influenced by the temperature. Both the conversion and selectivity for H₂ and CO are decreased markedly by increasing the CH₄/O₂ ratio in the feed. The catalyst dilution resulted in a small but significant decrease in both the conversion and selectivity for H₂ and CO. The increase in the catalyst particle size had also a small but significant effect on both the conversion and selectivity in the oxidative conversion process. Both the heat and mass transfer processes seem to play significant roles in the oxidative conversion of methane to syngas at a very low contact time or very high space velocity (5.1×10⁵ cm³ g⁻¹ h⁻¹).     

基于反应分子动力学的1-丁基-3-甲基咪唑硝酸盐与煤反应机理研究

使用FTT锥形量热仪对烟煤和烟煤-[Bmim][NO₃](1-丁基-3-甲基咪唑硝酸盐)混合物进行燃烧性能测试,并结合分子反应动力学方法(ReaxFF)分析1200K,1600K,1800K和2200K四个温度条件下[Bmim][NO₃]与煤的化学反应过程。实验结果表明:[Bmim][NO₃]的添加会使体系达到热释放速率(HRR)峰值的时间提前,即促进烟煤的氧化燃烧反应。模拟结果表明:当模拟温度为1200K时,仅产生了少量H₂O和NO₂;当模拟温度升高至1600K时,开始产生小分子烷烃、CO和CO₂,但数目较少且产生时间延后;当模拟温度继续升高至1800K时,开始产生少量的H₂等气体无机物,CO与CO₂的数目较1600K时增加一倍,且初次出现时间提前约100ps;当模拟温度为2200K时,反应物中的N元素转化为NH₃和HCN,CO数目继续增加,CO₂数目逐渐降低。总体来看,温度较低时反应过程主要受[NO₃]-影响,[NO₃]-通过与煤分子中羧基反应使煤分子脱氢形成得电子结构,从而易于发生分解反应;当温度继续升高,[Bmim]+开始显著参与反应过程,[Bmim]+热解产生的自由基与煤分子发生反应,生成大量NH₃和HCN,从而会对人体和环境造成危害。     

Catalytic reduction of sulfur dioxide using hydrogen or carbon monoxide over Ce1−xZrxO2 catalysts for the recovery of elemental sulfur

This study focuses on the direct sulfur recovery process (DSRP), in which SO₂ can be directly converted into elemental sulfur using a variety of reducing agents over Ce_1−xZr_xO₂ catalysts. Ce_1−xZr_xO₂ catalysts (where x = 0.2, 0.5, and 0.8) were prepared by a citric complexation method. The experimental conditions used for SO₂ reduction were as follow: the space velocity (GHSV) was 30,000 ml/g_-cat h and the ratio of [CO (or H₂, H₂ + CO)]/[SO₂] was 2.0. It was found that the catalyst and reducing agent providing the best performance were the Ce_0.5Zr_0.5O₂ catalyst and CO, respectively. In this case, the SO₂ conversion was about 92% and the sulfur yield was about 90% at 550 °C. Also, a higher efficiency of SO₂ removal and elemental sulfur recovery was achieved in the reduction of SO₂ with CO as a reducing agent than that with H₂. In the reduction of SO₂ by H₂ over the Ce_0.5Zr_0.5O₂ catalyst, SO₂ conversion and sulfur yield were about 92.7% and 73%, respectively, at 800 °C. Also, the reduction of SO₂ using synthetic gas with various [CO]/[H₂] molar ratios over the Ce_0.5Zr_0.5O₂ catalyst was performed, in order to investigate the possibility of using coal-derived gas as a reducing agent in the DSRP. It was found that the reactivity of the SO₂ reduction using the synthetic gas with various [CO]/[H₂] molar ratios was increased with increasing CO content of the synthetic gas. Therefore, it was found that the Ce_1−xZr_xO₂ catalysts are applicable to the DSRP using coal-derived gas, which contains a larger percentage of CO than H₂.     

Zn(Ⅱ)配合物催化C—C键裂解和原位合成2-甲基-4(3H)-喹唑酮

在配合物的水热合成过程中往往可以发现新的化学反应和催化机理。本文通过[Zn(L)₂·(H₂O)₂·(NO₃)₂]（L=4(3H)-喹唑酮）配合物在130℃催化乙腈分子中的CC键断裂,原位合成化合物2-甲基-4(3H)-喹唑酮。利用红外、元素分析和X射线单晶衍射表征分析2-甲基-4(3H)-喹唑酮和[Zn(L)₂·(H₂O)₂·(NO₃)₂]的结构,结果表明[Zn(L)₂·(H₂O)₂·(NO₃)₂]和2-甲基-4(3H)-喹唑酮属于三斜晶系,P-1空间群。三组温度控制实验表明,温度对2-甲基-4(3H)-喹唑啉酮的形成有着重要的影响,并且温度高于130℃有利于该催化反应的进行。采取电喷雾质谱表征2-甲基-4(3H)-喹唑酮的形成机理发现,[Zn(L)₂·(H₂O)₂·(NO₃)₂]催化乙腈分子中的CC键断裂,生成(CN)₂和·CH₃。·CH₃有选择性地引入到4(3H)-喹唑酮中的C原子和N原子之间。本文对原位引入CH₃有着指导作用。     

Reaction and oxygen permeation studies in Sm0.4Ba0.6Fe0.8Co0.2O3 − δ membrane reactor for partial oxidation of methane to syngas

A disk-type Sm_0.4Ba_0.6Co_0.2Fe_0.8O_3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H₂). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH₄ diluted with Ar. While CH₄ conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH₄ conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH₄ compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH₄ was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H₂ was fed. It is implied that the oxidation of CO and H₂ with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO₂ and H₂O react with CH₄ by reforming reactions to form syngas.