Department of Civil and Environmental Engineering , The Hong Kong Polytechnic University , Hong Kong , China.
Department of Science and Environmental Studies , The Education University of Hong Kong , Hong Kong , China.
Environ Sci Technol. 2019 Sep 17;53(18):10906-10916. doi: 10.1021/acs.est.9b03197. Epub 2019 Sep 5.
Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnO-CeO was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnO-CeO with exposed {111} facet showed higher activity for formaldehyde oxidation and CO selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid-base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnO-CeO-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong.
晶面控制表面活性配合物的形成，工程特定晶面有利于提高常规过渡金属氧化物的催化活性，常规过渡金属氧化物在低温下往往会失活。在此，我们通过合成 MnO-CeO 来调控三种主要晶面的暴露，揭示了它们在氧空位形成和定量效应、催化活性位和活性位行为方面的独特表面活性配合物。与另外两个低指数晶面{110}和{001}相比，暴露{111}晶面的 MnO-CeO 对甲醛氧化和 CO 选择性具有更高的活性。然而，尽管{110}晶面产生了更多的氧空位，但它并没有提高活性。氧空位在{111}晶面上高度稳定，其体相晶格氧具有较高的迁移率，可以补充表面晶格氧的消耗，这与活性和稳定性有关。在以{111}为主导的表面上暴露了高催化活性区，其中占主导地位的路易斯酸碱性质促进了氧的迁移和活化。通过原位 X 射线光电子能谱和漫反射红外傅里叶变换光谱相结合的方法考察了甲醛的矿化途径。随后，将 MnO-CeO-111 催化剂放大为家用空气净化器的过滤基板。在现场试点测试中，空气净化器启动 8 小时后，甲醛的平均浓度达到了香港室内空气质量指标的优秀等级。
