Catalytic oxidation of methane to methanol over Cu-CHA with molecular oxygen
Catalytic oxidation of methane to methanol over Cu-CHA with molecular oxygen
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DOI：
10.1039/d1cy00676b
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发表时间：
2021-07-20
影响因子：
5
通讯作者：
Ohyama, Junya
中科院分区：
文献类型：
--
作者：
Hirayama, Airi;Tsuchimura, Yuka;Ohyama, Junya
由于CH 4的高稳定性和CH 3OH的相对高的反应性，使用O-2将CH 4直接氧化成CH 3OH是具有挑战性的。在此，测试Cu-CHA沸石用于CH 4的直接氧化。与先前报道的其它沸石包括莫尔、KOR、MFI和FAU沸石相比，使用CHA型沸石改进了在CH 4-O-2-H 2 O流动反应中的CH 3 OH的催化生产。原位X射线吸收精细结构（XAFS）研究表明，Cu-CHA的高催化活性来源于其氧化还原特性，特别是参与CH 4活化的Cu 2+的高还原性。改变反应气体浓度以找到Cu-CHA上的最佳反应条件。此外，本文还利用CD 4、O-18（2）和D2 O等气体，从气体浓度和同位素气体效应两个方面对CH 4在Cu-CHA上的直接氧化反应机理进行了研究。CH_3OH的选择性取决于CH_3OH的氧化速率，而CH_3OH的氧化速率受Cu-CHA上O-_2和OH基团活化速率的影响。
Direct oxidation of CH4 to CH3OH using O-2 is challenging because of the high stability of CH4 and the relatively high reactivity of CH3OH. Here, Cu-CHA zeolites are tested for the direct oxidation of CH4. Catalytic production of CH3OH in a CH4-O-2-H2O flow reaction is improved using CHA type zeolites compared to other zeolites including MOR, BEA, MFI, and FAU zeolites reported previously. In situ X-ray absorption fine structure (XAFS) spectroscopy reveals that the high catalytic activity of Cu-CHA is derived from its redox properties, particularly, the high reducibility of Cu2+ involved in CH4 activation. The reaction gas concentrations are varied to find the optimized reaction conditions on Cu-CHA. In addition, the reaction mechanism of the direct CH4 oxidation on Cu-CHA is investigated based on not only the effects of gas concentrations but also the isotope gas effects using CD4, O-18(2), and D2O. It is suggested that the rate-determining step is the C-H activation of CH4, and the selectivity of CH3OH is determined by the oxidation rate of CH3OH, which is affected by the O-2 and OH group activation rate on Cu-CHA.