VOx-MoOx/TiO2催化剂低温催化降解一氯苯及二英的研究

垃圾焚烧过程中会产生大量氯苯等氯代挥发性有机污染物(CVOCs)和二噁英等持久性有机污染物(POPs). CVOCs的排放会导致光化学烟雾和温室效应的产生，而二噁英能在土壤中长期附存，具有人体致癌和致畸变等严重危害. 催化降解技术具有显著优势，能将二噁英等有机污染物彻底破坏分解，最终将其转化为CO₂、H₂O和HCl等产物. 基于钒基催化剂VO_x/TiO₂的过渡金属氧化物催化剂已被广泛应用于烟气CVOCs和二噁英处理领域. 钒基氧化物VO_x中的V=O基团对二噁英起到亲核吸附的作用，在钒基氧化物上添加第二活性组分钼氧化物MoO_x可以提高催化剂的催化活性. 本文采用湿法浸渍的方法制备出用于催化降解含氯污染物的粉体钒钼钛VO_x-MoO_x/TiO₂催化剂，并分析其合成方法、催化表征和性能测试结果，讨论反应温度对一氯苯及二噁英催化率影响的机理，旨在为开发二噁英催化技术提供参考. 结果表明:VO_x-MoO_x/TiO₂催化剂表面催化活性位点较多，活性组分分散良好，起始还原温度较低，活性氧含量较多，比表面积较大，颗粒团聚较轻，具有优良的催化特性. 通过系列实验筛选出合适的催化剂组分比例为5%VO_x-5%MoO_x/TiO₂(记作“V5-Mo5-Ti”，即VO_x和MoO_x的质量分数各占5%，TiO₂的质量分数占90%)，在150 ℃低温下其对一氯苯和二噁英的催化效果优异. V5-Mo5-Ti催化剂对一氯苯的低温转化率随原始稳定浓度和空速比的升高而降低. 在一氯苯初始浓度为150×10?6、空速比为10 000 h?1时，V5-Mo5-Ti催化剂在150 ℃下对一氯苯的转化率为54.0%，在300 ℃时接近100%. 在150 ℃的低温环境中，该催化剂对二噁英催化脱除率在86%以上，催化降解率在74%以上. 研究显示，VO_x-MoO_x/TiO₂催化剂对二噁英的催化脱除率和降解率随温度的升高而提高，主要归因于升温加快了V₂O₅中V5+和V4+元素以及MoO₃中Mo6+和Mo4+元素的催化氧化循环速率. 

Low Temperature Catalytic Degradation of Chlorobenzene and PCDD/Fs over VOx-MoOx/TiO2 Catalyst

In the process of waste incineration, a large amount of chlorinated volatile organic pollutants (CVOCs) such as chlorobenzene and persistent organic pollutants (POPs) such as PCDD/Fs are generated. The emission of CVOCs will lead to photochemical smoke and the greenhouse effect. PCDD/Fs can exist in soil for a long time, causing serious consequences such as carcinogenesis and teratogenesis to the human body. Catalytic degradation technology has significant advantages in PCDD/Fs treatment, which can completely destroy and decompose organic pollutants and convert them into CO₂, H₂O, HCl and other products. Transition metal oxide catalysts based on VO_x/TiO₂ have been widely used in the treatment of flue gas CVOCs and PCDD/Fs. The V=O group in VO_x plays the role of nucleophilic adsorption of PCDD/Fs. Adding the second active component MoO_x to vanadium-based oxide can improve the catalytic activity of the catalyst. In this study, a series of powder catalysts of VO_x-MoO_x/TiO₂ for catalytic degradation of CVOCs were prepared by wet impregnation method. The synthesis method, catalytic characterization and performance test results of VO_x-MoO_x/TiO₂ catalyst were analyzed. The influence mechanism of reaction temperature on the catalytic degradation rate of chlorobenzene (CB) and PCDD/Fs was discussed, providing reference for expanding PCDD/Fs catalytic technology. The results show that VO_x-MoO_x/TiO₂ catalyst has excellent catalytic activities, which is attributed to its abundant surface catalytic active sites, good dispersion of active components, low initial reduction temperature, high active oxygen content, large specific surface area, and less particle agglomeration. Through a series of experiments, the formulation of 5%VO_x-5%MoO_x/TiO₂ (denoted as ‘V5-Mo5-Ti’, the mass fraction of VO_x and MoO_x respectively accounts for 5% and the mass fraction of TiO₂ accounts for 90%) with the highest catalytic activities was developed, which showed excellent catalytic activities on both CB and PCDD/Fs at the low temperature of 150 ℃. The conversion rate of V5-Mo5-Ti at low temperature was increased as the initial concentration and gas hourly space velocity (GHSV) increased. When the initial concentration of CB was 150×10?6 and the GHSV was 10,000 h?1, the conversion rate of CB by V5-Mo5-Ti was 54.0% at 150 ℃ and was close to 100% at 300 ℃. At low-temperature (150 ℃), the removal rate of PCDD/Fs was higher than 86%, and the catalytic rate was higher than 74%. The research shows that the catalytic removal rate and degradation rate of PCDD/Fs by VO_x-MoO_x/TiO₂ catalyst increased with the increase of reaction temperature, attributing to the accelerated oxidation cycle rate of V5+ and V4+ in V₂O₅ and Mo6+ and Mo4+ in MoO₃.