Combined Single-pass Conversion of Methane Via Oxidative Coupling and Dehydro-aromatization

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO–La₂O₃/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate constant of the overall process revealed about 1.5×10⁻⁶ s⁻¹. Up to 72 h on stream, the yield of aromatics was still maintained at 5.0% with a methane conversion of 9.6%, which is obviously higher than that reported for the conventional MDA process with single catalyst. Upon the TPR results, this wonderful enhancement would be attributed to an in-situ formation of CO₂ and H₂O through the OCM reaction, which serves as a scavenger for actively removing the coke formed during the MDA reaction via a reverse Boudouard reaction and the water gas reaction as well.     

甲烷氧化偶联制乙烯工艺研究进展

甲烷氧化偶联(OCM)途径是通过一步法获取乙烯,是现有乙烯生产中最为简捷的工艺。本文综述了该工艺催化剂系统、反应机理、工艺开发研究的新进展,并探讨了OCM过程面临的关键问题有催化剂的选择、反应器和反应流程的设计和反应温度的控制。     

LiCl/MnO_2-H_3BO_3体系甲烷氧化偶联催化剂的研究

由于石油资源的日见枯竭 ,天然气在化工原料中的地位日益突出。对天然气的主要成分甲烷、氧化偶联 (OCM)制备乙烯的催化剂—— Li Cl/Mn O2 - H3 BO3 进行了系统研究并探讨了其组分及外界反应条件对该催化剂性能的影响 ,发现了可能的活性组分 :立方晶型的 Li4 B7O12 Cl。     

Surface Praseodymium Species on MgO: Characterization and Activity for Oxidative Coupling of Methane

On pulsing CH₄ over MgO containing various amounts of praseodymium oxide (PrO_x) at 1023 K, the CH₄ conversion decreased with increasing pulse number, and both the initial activity and selectivity to C₂ products (corresponding to the first pulse) decreased with increasing PrO_x content. Characterization by XRD, SEM-EDX and XPS showed calcined materials to contain well-dispersed PrO_x (x = 1·83–2) at low Pr concentrations, but only crystalline PrO_1·83 at high (10 wt%) Pr concentration. A PrO_1·83 phase was present at all Pr concentrations after the He treatment at 1023 K, and PrO_1·83, PrO_1·75 and PrO_1·5 after reaction. © 1997 SCI     

Higher Hydrocarbon Production through Oxidative Coupling of Methane Combined with Hydrogenation of Carbon Oxides

In the production of higher hydrocarbons, combining oxidative coupling of methane (OCM) with hydrogenation of the formed carbon oxides in a separate reactor provides an alternative to the currently applied methane conversion to syngas followed by Fischer‐Tropsch synthesis. The effects of CH₄:O₂ feed ratio in the OCM reactor and partial pressures of H₂ or/and H₂O in the hydrogenation reactor were analyzed to maximize production of C₂₊ hydrocarbons and reduce CO_x formation. The highest C₂₊ yield was achieved with low CH₄:O₂ feed ratio for OCM and removal of the formed water before entering the hydrogenation reactor.     

Hydrothermal Post-synthesis of HZSM-5 Zeolite to Enhance the Coke-resistance of Mo/HZSM-5 Catalyst for Methane Dehydroaromatization

Hydrothermal post-synthesis was used to modify the micropores and acidity of commercially available HZSM-5 zeolites. The recrystallization and the dynamic incorporation and extraction of the framework Al not only stabilized the framework with high crystallinity, but also inhibited the creation of extra-pores during the post-synthesis in NaOH aqueous solution. The resulted Mo/HZSM-5 catalyst showed rather high catalytic stability and greatly enhanced selectivity towards aromatics for methane dehydroaromatization reaction by effectively inhibiting the coke formation.     

甲烷氧化偶联制C2烃催化剂及催化反应机理研究进展

综述了甲烧氧化偶联制乙烷、乙烯催化剂及催化机理研究概况。重点介绍1989年以来对碱及碱土金属化合物、烯土氧化物、复合氧化物等各类催化剂的研究进展。对目前催化剂上甲烷活化途径、甲基自由基在反应过程中的作用机理、不同氧化物种及表面酸、碱位与催化性能的关系等方面的研究抉况及不同观点也作了简介。     

SrTiO3体系上甲烷氧化偶联催化性能及XPS表征

用X-光电子能谱（XPS）研究SrTiO2体系上不同Sr/Ti比、B位不同价态掺杂元素和掺杂量的催化剂组成、表面吸附氧含量与甲烷氧化偶联（OCM）催化性能.结果表明Sr/Ti比增加、B位掺杂元素（Zr,Al,Mg）价态降低和B位Mg2＋掺杂量增加会导致催化剂表面吸附氧含量的增加,并与催化剂的C2产物选择性有顺变关系,但表面吸附氧含量过高会导致甲烷的深度氧化.     

Critical Influence of Mn on Low-Temperature Catalytic Activity of Mn/Na2WO4/SiO2 Catalyst for Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) was investigated in the temperature range 370-775 °C over Mn/Na₂WO₄/SiO₂ catalysts with different loadings of manganese in integral-mode conditions. Na₂WO₄/SiO₂ shows no activity at low temperature (370 °C), whereas Mn-doped catalyst exhibits 14% C²⁺ yield under similar reaction conditions, indicating that manganese plays a critical role in low-temperature methane coupling reaction. Partial pressure of oxygen in the feed also influences the low-temperature OCM activity of the catalysts.     

Thermal Reaction Analysis of Oxidative Coupling of Methane

For more than three decades, the oxidative coupling of methane (OCM) process has been investigated as a promising alternative approach for ethylene production. Simulations of different sets of surface mechanisms over the Na₂WO₄/Mn/SiO₂ catalyst and the gas phase reactions that come along with the OCM reaction were analyzed in a fixed‐bed, membrane, and fluidized‐bed reactor. The results were compared with the experimental data generated in an OCM mini‐plant. It was observed that the gas phase reactions are crucial in reducing the overall selectivity, especially in the fluidized‐bed reactor.     

Highly Stable Performance of Methane Dehydroaromatization on Mo/HZSM-5 Catalyst with a Small Amount of H2 Addition into Methane Feed

With a small amount of H₂ (3 6%) addition into methane feed, coke formation on 6 wt% Mo catalyst during the methane dehydroaromatization reaction was effectively suppressed and the catalyst stability was increased evidently under the reaction conditions of 1023K, 0.3MPa and 2520 mL g-MFI^-1 h^-1 of methane space velocity.     

Oxidant Activation Over Structural Defects of Oxide Catalysts in Oxidative Methane Coupling

Different aspects concerning the process of direct methane conversion to oxygen-containing products developed during more than half a century have been considered in previous reviews [1-3]. In particular, Gesser et al. [13 paid most attention to the homogeneous stages in methane conversion, while Foster [2] and Pitchai and Klier [3] examined the effect of different catalysts on methanol and formaldehyde formation. At present the main product of the homogeneous methane oxidation process with oxygen is shown to be methanol formed according to a chain-branching mechanism. In the presence of homogeneous initiators [4] (benzene, 2,2,4- trimethylpentane, etc.) or heterogeneous catalysts [2,3,5,6], formaldehyde is formed together with CH30H. However, the yield of the desirable products is low and does not exceed 8-10%. Charged atomic oxygen forms are considered to take part in the process of catalytic methane oxidation.     

Comparison of Alkali Metal Promoted MgO Catalysts for Their Surface Acidity/Basicity and Catalytic Activity/Selectivity in the Oxidative Coupling of Methane

Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0·1) calcined at 750°C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C₂-hydrocarbons at different temperatures (700–750°C), CH₄/O₂ ratios (4·0 and 8·0) in feed, and space velocities (10320 cm³ g⁻¹ h⁻¹). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C₂-hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750°C, the best performance in the OCM is shown by Li–MgO (at 750°C). © 1997 SCI.     

SrTiO3超细微粒的制备与甲烷氧化偶联催化性能

采用溶胶－凝胶法合成钙钛矿型立方相SrTiO3超细微粒,探讨了成胶温度,配体,溶剂以及干凝胶热处理条件对生成SrTiO3微粒粒度,均匀性及比表面积的影响,用TGA－DTA,IR,TEM,XRD,XPS,BET表面积测试等手段对SrTiO3超细微粒的形成机制,结构及形貌和甲烷氧化偶联催化性能进行了研究,发现SrTiO3超细微粒对于甲烷低温（~650℃）氧化偶联催化性能明显优于固相反应法制备的大粒子SrTiO3催化剂。     

Autothermal Methane Oxidative Coupling Process over La2O3/MgO Catalysts

Some essential conditions necessary to reach an autothermal regime in methane oxidative coupling on La₂O₃/MgO catalysts were investigated. The following three ways can be suggested to transfer the process into the autothermal regime: (1) higher initial concentrations of reagents; (2) larger reactor diameter; (3) optimization of the flow rate and the preheating temperature. It was found that the optimal temperature of the autothermal regime of methane oxidative coupling is governed by the nature of the catalyst.     

Effect of Electronic Properties of Catalysts for the Oxidative Coupling of Methane on Their Selectivity and Activity

The oxidative coupling of methane (OCM) to higher hydrocarbons may eventually become an interesting alternative for the chemical utilization of natural gas. Extensive studies have been conducted since the works of Keller and Bhasin [l] and of Hinsen and Baerns [2].     

Effect of Electronic Properties of Catalysts for the Oxidative Coupling of Methane on Their Selectivity and Activity

The oxidative coupling of methane (OCM) to higher hydrocarbons may eventually become an interesting alternative for the chemical utilization of natural gas. Extensive studies have been conducted since the works of Keller and Bhasin [l] and of Hinsen and Baerns [2].     

A Critical Assessment of Li/MgO-Based Catalysts for the Oxidative Coupling of Methane

Li/MgO is one of the most frequently investigated catalysts for the oxidative coupling of methane. Besides catalytic testing, it is also a suitable system to perform surface science experiments and quantum chemical calculations, which is not possible for many other active catalysts. However, the real structure of Li/MgO, the nature of the active center and the structure - activity relationship remain unclear, despite all the research that has been done. The aim of this review is to summarize the available knowledge on Li/MgO to structure and accelerate and improve the ongoing work on this catalytic system.