基于XRD和FITR的Ce-V-Ti催化剂减排烧结烟气二噁英的活性分析

二噁英是一类含氯挥发性有机污染物，具有环境持久性、生物蓄积性和长期残留性等特性，可造成致畸、致癌和致突变等危害。铁矿烧结过程中含氯前驱物在碱性环境下通过Ullman反应或经飞灰中某些催化性成分催化生成二噁英；碳、氢、氧和氯等元素可通过基元反应“从头合成”(de novo)二噁英，是二噁英最主要的排放源之一。物理吸附技术仅能实现污染物由气相向固相转移，加重了飞灰处理负担，并存在特定温度条件下(250～350 ℃)二噁英再生风险。催化降解技术能彻底矿化有机污染物，生成CO₂，H₂O和HCl/Cl₂，是一种避免二次污染高效节能、成本较低的方法。但由于传统催化剂活性温度区间较高，无法达到烧结烟气末端温度。选择合适的催化剂，提高催化剂低温降解活性，能实现低温、高效催化降解烧结烟气中有机污染物的目标。过渡金属Ce具有稀土金属的4f轨道配位效应和路易斯酸活性位点，对有机污染物C-H和C-Cl键活化起到至关重要的作用，掺杂过渡金属、调整活性组分比例可进一步提高铈基催化剂的抗中毒性能和降解活性。因此，本文采用溶胶凝胶法制备Ce-V-Ti复合催化剂，以氯苯为二噁英模型分子，研究了不同活性组分比例对铈基催化剂降解烧结烟气中二噁英活性影响。利用X射线衍射仪、比表面积及孔径测定仪和拉曼光谱仪对催化剂进行表征，研究Ce-V-Ti催化剂的相组成、比表面积和分子结构，并推测铈基催化剂的降解机理。结果表明，在实验室模拟烧结烟气气氛下，反应条件为GHSV=30 000 h-1、20%O₂和100 ppm CB，当Ce质量分数为15%、V质量分数为2.5%时，Ce-V-Ti催化降解氯苯活性最高，150 ℃能达到约60%转换率，300 ℃能实现95%降解率。催化剂载体与活性组分之间化学交互作用，影响催化剂的降解活性。通过光谱学分析发现，Ce-V-Ti催化剂XRD图谱主要为锐钛矿相的TiO₂，比表面积为95.53 m2·g-1，孔容0.29 cm3·g-1，孔径6.5 nm。表面官能团主要为C-H基团和H-O官能团。引入V作为Ce-Ti催化剂助剂，促进了Ce元素固溶，增加了催化剂表面氧空位，有利于提升催化剂降解活性。通过对催化剂机理分析，认为反应物首先通过发生亲核取代而垂直吸附于催化剂表面，再被活性组分Ce活化，活化后氯苯分子被表面活性氧分解矿化。同时，过渡金属V的低价态氧化物发生氧化反应，促进Ce的还原反应。

Study on Catalytic Combustion of Dioxins From Iron Ore Sintering Flue Gas Over Ce-V-Ti Catalysts by XRD and FTIR

Dioxins are a group of chlorinated volatile organic pollutants(VOCs)with environmental persistence,biological accumulation and long-term residual properties.It can cause teratogenic,carcinogenic and mutagenic hazards.During the iron ore sintering process,dioxins can be catalytically synthesized from chlorine-containing precursors by Ullman reaction in the alkaline environment or by some catalytic components on the surface of fly ash.Besides,dioxins can be synthesized by de novo through elementary reaction.Iron ore sintering process is one of the most emission sources of dioxins.Physical adsorption technology can only remove pollutants from gas phase to the solid phase and increase the aftertreatment problem of fly ash.Besides,there is a risk of dioxins regeneration under 250~350℃.Catalytic combustion can be completely degradation dioxins into CO2,H2O and HCl/Cl2 over catalysts.It is an efficient,energy conservation and low-cost method to avoid secondary pollution.However,the working temperature of traditional catalysts is too high to the end temperature of the sintering flue gas.It is important to improve the catalytic activity at low temperature to achieve high efficiency catalytic combustion of VOCs from iron ore sintering flue gas.As Ce has the 4 f orbital coordination effect and Lewis acid site,which plays a crucial role in the activation of C—H and C—Cl bonds in organic pollutants,the anti-chlorine toxicity and combustion activity of the catalystcan be improved by doping transition metal or adjusting the proportion of active components of catalysts.Hence,the effect of different Ce/V weight ratio of Ce-V-Ti catalysts prepared by sol-gel method were studied in this paper.Chlorobenzene was used as the model molecule of dioxins.The phase,specific area,molecular structure and functional groups of Ce-V-Ti catalysts were characterized by XRD,BET,XPS and FTIR.The results show that the catalytic activity of chlorobenzene over Ce-V-Ti catalysts with 15 Wt% Ce and 2.5 Wt% V can achieve CB conversion of 60% at 150℃ and 95% at 300℃ under the reaction conditions of GHSV=30000 h^-1,20%O2 and 100 ppm CB.The chemical interaction between the barrier and the active component affected the catalytic activity of catalysts.According to the spectroscopic analysis,the XRD pattern of Ce-V-Ti catalysts was mainly anatase TiO2.The specific surface area was 95.53 m^2·g^-1,the volume of the pore was 0.29 cm^3·g^-1,and DBJH was 6.5 nm.Most of the functional groups on the Ce-V-Ti catalysts were C—H groups and O—H,which was expedited the adsorption and desorption of CB.The introduction of V as co-catalytic compositioninto Ce-Ti catalyst promoted the solid solution reaction of Ce element and increased the oxygen vacancy on the surface of the catalyst,which was conducive to improving the catalytic activity of the catalyst.Meanwhile,the oxidation reaction of V in low-price promotes the reduction reaction of Ce.