采用水热法分别合成了α-, β-, γ-MnO₂纳米棒, 使用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、氢气程序升温还原(H₂-TPR)和X射线光电子能谱(XPS)等技术对三种晶型MnO₂纳米棒的结构和形貌进行了表征, 并以氯苯(CB)为探针考察了其催化活性和稳定性. 结果表明, 三种晶型MnO₂纳米棒在低温范围内均有较高的催化活性, 且活性顺序为α-MnO₂＞γ-MnO₂＞β-MnO₂. 此外, 还发现三种晶型MnO₂纳米棒比无定形MnO₂有更强的抗氯中毒能力. 在三种晶型MnO₂纳米棒中, α-MnO₂纳米棒催化氧化氯苯的活性最佳, 主要是由于该种MnO₂纳米棒含有丰富的晶格氧并且具有较强的可还原能力.

Mn-containing catalysts are widely used owing to their excellent redox properties, while in most cases they would deactivate to some extent in the oxidation process of the chloride volatile organic compounds (CVOCs) due to chlorine poisoning. In this work α-, β-, γ-MnO₂ nanorods were synthesized via a hydrothermal route, and their catalytic performance for chlorobenzene (CB, as a model of CVOCs) and resistance to chlorine poisoning were studied. The results showed that the MnO₂ nanorods with different phase structures exhibited high activities for low temperature catalytic oxidation of CB, and the catalytic activities of the MnO₂ nanorods depended on the crystal phase of MnO₂, following in the order of α-MnO₂＞γ-MnO₂＞β-MnO₂. Moreover, the MnO₂ nanorods showed high resistance to chlorine poisoning compared to the amorphous MnO₂. The experiment results indicated that the conversion of CB over α-, β-, γ-MnO₂ nanorods at 250 ℃ remained stable at about 98%, 82% and 90% respectively for 35 h. Contrasted to MnO₂ nanorods, the conversion of CB over amorphous MnO₂ dropped from 80% to 32% in the same condition. Additionally, the as-synthesized MnO₂ nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). XRD results showed that the crystallinity of α-, β-, γ-MnO₂ nanorods were different, and decreased in the order: β＞α＞γ, implying that the crystallinity of α-, β-, γ-MnO₂ nanorods had no significant effect on its catalytic performance. SEM and TEM showed that three kinds of nanorods were well dispersed, and exhibited one-dimensional nanorods. H₂-TPR and XPS results demonstrated that the high catalytic activity of α-MnO₂ nanorods resulted from their rich lattice oxygen and good reducibility. Therefore, the enrichment of the lattice oxygen with excellent reducibility was considered as main reason of high activity of α-MnO₂ nanorods for low temperature catalytic destruction of CB.