关键词: α-, β-, γ-MnO₂, 纳米棒, 晶型, 氯苯, 催化燃烧

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.

Key words: α-, β-, γ-MnO₂, nanorods, phase structure, chlorobenzene, catalytic combustion