Park Min Bum, Park Eun Duck, Ahn Wha-Seung
Innovation Center for Chemical Engineering, Department of Energy and Chemical Engineering, Incheon National University, Incheon, South Korea.
Department of Chemical Engineering and Department of Energy Systems Research, Ajou University, Suwon, South Korea.
Front Chem. 2019 Jul 17;7:514. doi: 10.3389/fchem.2019.00514. eCollection 2019.
The conversion of methane into an easily transportable liquid fuel or chemicals has become a highly sought-after goal spurred by the increasing availability of cheap and abundant natural gas. While utilization of methane for the production of syngas and its subsequent conversion via an indirect route is typical, it is cost-intensive, and alternative direct conversion routes have been investigated actively. One of the most promising directions among these is the low-temperature partial oxidation of methane to methanol over a metal-loaded zeolite, which mimics facile enzymatic chemistry of methane oxidation. Thus mono-, bi-, and trinuclear oxide compounds of iron and copper stabilized on ZSM-5 or mordenite, which are structurally analogous to those found in methane monooxygenases, have demonstrated promising catalytic performances. The two major problems of theses metal-loaded zeolites are low yield to methanol and batch-like non-catalytic reaction systems challenging to extend to an industrial scale. In this mini-review, attention was given to the direct methane oxidation to methanol over copper-loaded zeolite systems. A brief introduction on the catalytic methane direct oxidation routes and current status of the applied metal-containing zeolites including the ones with copper ions are given. Next, by analyzing the extensive experimental and theoretical data available, the consensus among the researchers to achieve the target of high methanol yield is discussed in terms of zeolite topology, active species, and reaction parameters. Finally, the recent efforts on continuous methanol production from the direct methane oxidation aiming for an industrial process are summarized.
随着廉价且丰富的天然气供应日益增加，将甲烷转化为易于运输的液体燃料或化学品已成为一个备受追捧的目标。虽然利用甲烷生产合成气并通过间接路线进行后续转化是常见的做法，但成本高昂，因此人们积极研究替代的直接转化路线。其中最有前景的方向之一是在负载金属的沸石上将甲烷低温部分氧化为甲醇，这模拟了甲烷氧化的简易酶促化学过程。因此，稳定在ZSM - 5或丝光沸石上的铁和铜的单核、双核和三核氧化物化合物，其结构与甲烷单加氧酶中的类似，已展现出有前景的催化性能。这些负载金属的沸石存在两个主要问题，即甲醇产率低以及类似间歇式的非催化反应体系难以扩展到工业规模。在这篇综述中，重点关注了负载铜的沸石体系中甲烷直接氧化为甲醇的过程。简要介绍了催化甲烷直接氧化路线以及包括含铜离子沸石在内的应用金属沸石的现状。接下来，通过分析现有的大量实验和理论数据，从沸石拓扑结构、活性物种和反应参数等方面讨论了研究人员为实现高甲醇产率目标所达成的共识。最后，总结了近期旨在实现工业过程的甲烷直接氧化连续生产甲醇的努力。
