Aimdate Kritchakorn, Srifa Atthapon, Koo-Amornpattana Wanida, Sakdaronnarong Chularat, Klysubun Wantana, Kiatphuengporn Sirapassorn, Assabumrungrat Suttichai, Wongsakulphasatch Suwimol, Kaveevivitchai Watchareeya, Sudoh Masao, Watanabe Ryo, Fukuhara Choji, Ratchahat Sakhon
Department of Chemical Engineering, Faculty of Engineering, Mahidol University, Nakhon Pathom 73170, Thailand.
Synchrotron Light Research Institute, Nakhon Ratchasima 30000, Thailand.
ACS Omega. 2021 May 18;6(21):13779-13794. doi: 10.1021/acsomega.1c01231. eCollection 2021 Jun 1.
Natural kaolin-based Ni catalysts have been developed for low-temperature CO methanation. The catalysts were prepared via a one-step co-impregnation of Ni and Ce onto a natural kaolin-derived metakaolin using a microwave-assisted hydrothermal method as an acid-/base-free synthesis method. The influences of microwave irradiation and Ce promotion on the catalytic enhancement including the CO conversion, CH selectivity, and CH yield were experimentally investigated by a catalytic test of as-prepared catalysts in a fixed-bed tubular reactor. The relationship between the catalyst properties and its methanation activities was revealed by various characterization techniques including X-ray fluorescence, X-ray diffraction, Brunauer-Emmett-Teller, scanning electron microscopy, selected area electron diffraction, transmission electron microscopy, elemental mapping, H temperature-programmed reduction, and X-ray absorption near-edge structure analyses. Among the two enhancement methods, microwave and Ce promotion, the microwave-assisted synthesis could produce a catalyst containing highly dispersed Ni particles with a smaller Ni crystallite size and higher catalyst reducibility, resulting in a higher CO conversion from 1.6 to 7.5% and a better CH selectivity from 76.3 to 79.9% at 300 °C. Meanwhile, the enhancement by Ce addition exhibited a great improvement on the catalyst activities. It was experimentally found that the CO conversion increased approximately 7-fold from 7.5 to 52.9%, while the CH selectivity significantly improved from 79.9 to 98.0% at 300 °C. Though the microwave-assisted synthesis could further improve the catalyst activities of Ce-promoted catalysts, the Ce addition exhibited a more prominent impact than the microwave enhancement. Cerium oxide (CeO) improved the catalyst activities through mechanisms of higher CO adsorption capacity with its basic sites and the unique structure of CeO with a reversible valence change of Ce and Ce and high oxygen vacancies. However, it was found that the catalyst prepared by microwave-assisted synthesis and Ce promotion proved to be the optimum catalyst in this study. Therefore, the present work demonstrated the potential to synthesize a nickel-based catalyst with improved catalytic activities by adding a small amount of Ce as a catalytic promoter and employing microwave irradiation for improving the Ni dispersion.
已开发出用于低温CO甲烷化的天然高岭土基镍催化剂。采用微波辅助水热法，通过将镍和铈一步共浸渍到天然高岭土衍生的偏高岭土上制备催化剂，该方法为无酸碱合成法。通过在固定床管式反应器中对制备的催化剂进行催化测试，实验研究了微波辐射和铈促进对催化增强的影响，包括CO转化率、CH选择性和CH产率。通过各种表征技术揭示了催化剂性能与其甲烷化活性之间的关系，这些技术包括X射线荧光、X射线衍射、布鲁诺尔-埃米特-泰勒法、扫描电子显微镜、选区电子衍射、透射电子显微镜、元素映射、H程序升温还原和X射线吸收近边结构分析。在微波和铈促进这两种增强方法中，微波辅助合成可以制备出含有高度分散的镍颗粒、镍微晶尺寸更小且催化剂还原度更高的催化剂，从而在300℃时使CO转化率从1.6%提高到7.5%，CH选择性从76.3%提高到79.9%。同时，添加铈的增强作用对催化剂活性有很大改善。实验发现，在300℃时，CO转化率从7.5%增加到52.9%，提高了约7倍，而CH选择性从79.9%显著提高到98.0%。尽管微波辅助合成可以进一步提高铈促进催化剂的活性，但添加铈比微波增强表现出更显著的影响。氧化铈（CeO）通过其碱性位点具有更高的CO吸附能力以及CeO具有Ce和Ce的可逆价态变化和高氧空位的独特结构来提高催化剂活性。然而，发现通过微波辅助合成和铈促进制备的催化剂是本研究中的最佳催化剂。因此，目前的工作证明了通过添加少量铈作为催化促进剂并采用微波辐射来改善镍的分散性，从而合成具有改进催化活性的镍基催化剂的潜力。
