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Importance of water content in birnessite-type MnO2 catalysts for HCHO oxidation: Mechanistic details and DFT analysis
Chemosphere ( IF 8.8 ) Pub Date : 2021-09-18 , DOI: 10.1016/j.chemosphere.2021.132293
Changye Mang 1 , Jun Luo 1 , Pengxu Cao 1 , Xin Zhang 1 , Mingjun Rao 1 , Guanghui Li 1 , Tao Jiang 1
Affiliation  

Water is featured in an indispensable role during the process of catalytic oxidation of HCHO. In this work, a rich water-containing birnessite-type MnO2 was synthesized, and its water content was adjusted through calcination. Phase structure and texture properties of the prepared birnessite were characterized. It was revealed that three types of water (namely absorbed water, molecular water, and structural hydroxyl) existed in birnessite. With the loss of water content, the interlayer distance of samples had decreased which changed the structure of birnessite to cryptomelane. This converted the morphology from an initial layered shape to a rod-like shape. Besides, the underlying mechanism for this effect on HCHO catalytic oxidation was elucidated. Results indicated that hydroxyl groups could slowly and sequentially oxidize HCHO to DOM, formate, and carbonate species. The hydroxyl groups also promoted the formation of oxygen vacancy which could activate O2 to O− 2 and O. The hydroxyl groups which were consumed had originally been supplied by the reaction between O- 2, O, and H2O (absorbed and interlayer water in birnessite) which was then replenished from air stream. Clearly, water is favorable to the catalytic reaction. It is the main reason why birnessite can continuously decompose HCHO.



中文翻译:

水钠锰矿型 MnO2 催化剂中水含量对 HCHO 氧化的重要性:机理细节和 DFT 分析

水在 HCHO 的催化氧化过程中起着不可或缺的作用。在这项工作中,富含水的水钠锰矿型 MnO 2合成,并通过煅烧调节其含水量。表征了制备的水钠锰矿的相结构和织构特性。结果表明,水钠锰矿中存在三种水(即吸附水、分子水和结构羟基)。随着含水量的减少,样品的层间距减小,使水钠锰矿结构转变为钾锰矿。这将形态从最初的分层形状转变为棒状形状。此外,阐明了这种对 HCHO 催化氧化作用的潜在机制。结果表明,羟基可以缓慢且连续地将 HCHO 氧化为 DOM、甲酸盐和碳酸盐物质。羟基也促进了氧空位的形成,氧空位可以激活 O 2到 O− 2 和 O 。这被消耗的羟基最初是由反应O-之间供给2,O - 和H 2 O(吸收和层间水钠锰矿水),然后将其从空气流补充。显然,水有利于催化反应。这是水钠锰矿能不断分解HCHO的主要原因。

更新日期:2021-09-23
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