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挥发性有机物是主要的大气污染物之一,特别是其中的含氯挥发性有机物(chlorinated volatile organic compounds, CVOCs),被大多数国家列为高危害目标排放物. 该类污染物具有排放量大、毒性强、稳定性高和不易降解的特点. CVOCs主要来源于石化、医药、农药、轻工业等生产过程中,其大量排放对人类健康和生态环境造成危害[1-4]。鉴于此,世界各地展开了治理CVOCs废气的技术研究,探索出多种处理方法,主要包括[5-11]:直接燃烧法、吸收法、催化氧化法、生物法、低温等离子净化法等. 其中,催化氧化技术具有反应温度低、适用范围广、净化效率高以及二次污染物少等优点,已作为比较成熟的环保技术广泛地应用于CVOCs治理领域.
众所周知,催化剂是催化氧化反应过程中的关键因素之一,因此探索和开发高效、廉价、无污染的催化剂是CVOCs催化氧化研究中不可或缺的一部分. 目前,用于催化氧化CVOCs的催化剂主要包括贵金属、非贵金属和分子筛三类[12-18]. 贵金属催化剂如Pt(铂)、Pd(钯)、Ru(钌)、Au(金)、Rh(铑)等对CVOCs的催化活性相对较高,但价格昂贵,且容易与产物中含氯物种发生反应,形成含氯的金属有机物,造成催化剂中毒失活. 分子筛催化剂包括H-Y、HZSM-5、ZSM-5、SAPO-34、KIT-6、MCM-41以及各种沸石,其比表面积较大、耐久性优异,但容易产生积碳从而导致催化剂活性降低. 非贵金属氧化物包括过渡金属V、Cr、Mn、Fe、Co、Ni、Cu等金属,还包括镧系的Ce、La等. 尽管非贵金属催化剂催化效率不如贵金属,但仍具有足够的活性,并可通过掺杂改性得到进一步提高,且还具备成本低,来源广泛的优势. 其中,CeO2作为一种无毒且廉价的材料,因具有较高的储氧能力和丰富的氧空位而受到广泛关注[19- 20]. 最近的研究表明,与纯氧化铈相比,掺铜氧化铈具有更好的氧化还原性能和储氧能力,从而使得CuO@CeO2在催化反应中的活性甚至与贵金属催化剂相当[21-22]. 因此,铜掺杂氧化铈有望成为CVOCs催化降解的良好候选材料.
据报道,多孔CeO2基材料因其高比表面积和纳米孔隙率而显示出良好的氧化还原性能和优异的催化活性. 因此,CuO@CeO2材料中多孔结构的设计被认为是获得高催化活性和稳定性的重要策略. 金属有机骨架(Metal-organic frameworks,MOFs)材料由于其柔性和可控的组成而表现出多样性,并且作为多孔结构制备的前驱体极具吸引力[23-26]. 以MOFs为前驱体制备的金属氧化物不仅继承了母体MOFs的多孔结构和大的比表面积,克服了母体的不稳定性,并且,相比于其他制备方法活性组分分散更均匀,从而促进反应物分子的吸附和活化,有利于污染物的降解. 因此,本文采用了一种简单方法合成Ce-BTC,并通过负载、煅烧,制备出多孔CuO@CeO2双金属氧化物催化剂. 由于1,2-二氯苯的分子结构类似于剧毒的2,3,7,8-四氯二苯并二恶英(TCDD),且毒性相对较低、检测方便,因此常被用作CVOCs的模型化合物[27]. 本文便以1,2-二氯苯为目标污染物,采用微型固定床装置对催化剂低温催化降解CVOCs性能进行评价.
基于MOFs的CuO@CeO2双金属催化剂的制备及其对1,2-二氯苯的低温催化降解
CuO@CeO2 bimetallic catalyst derived from MOFs for the degradation of 1,2-dichlorobenzene at low temperature
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摘要: 以负载铜离子的均苯三甲酸铈-金属有机骨架(Ce-BTC)为前驱体,通过煅烧制备得到CuO/CeO2双金属氧化物催化剂. 通过XRD、SEM、BET、H2-TPR等手段对所制得催化剂的组成、结构、形貌等进行了表征.以1,2-二氯苯为模型化合物,采用固定床微反应装置对催化剂低温催化降解含氯挥发性有机物(CVOCs)性能进行评价.以金属有机骨架(MOFs)为模板制备的金属氧化物为具有较大比表面积的介孔材料. 通过对比实验发现,25%-CuO@CeO2具有较好的低温催化降解1,2-二氯苯性能.当反应温度为100、150、200 oC时,对1,2-二氯苯降解效率分别为64.5 %、94.4%、98.9%. 同时,该催化剂还表现出较高的稳定性. 当反应温度为150 oC时,催化剂经过连续反应后通过煅烧活化,再循环使用六次之后其催化降解效率仍然可达90%以上. 该催化材料表现出一定氧化活性和抗水性,当氧含量低于20%或含水量小于15%时,该催化材料对1,2-二氯苯催化降解效率能保持在90%以上.Abstract: The CuO@CeO2 bimetallic catalysts were prepared by calcining the precursor of cerium based metal-organic frameworks (MOFs) Ce-BTC (BTC = 1,3,5-benzenetricarboxylic acid) loaded with copper ions. The composition, structure and morphology of the catalysts were characterized by XRD, SEM, BET and H2-TPR. A fixed bed micro reactor was employed to study the catalytic degradation of chlorinated volatile organic compounds (CVOCs) on catalysts at low temperature. The metal oxides derived from MOFs are mesoporous materials with large specific surface area. The catalyst of 25%-CuO@CeO2 showed better catalytic degradation performance for 1,2-dichlorobenzene at low temperature through comparative experiment. The degradation efficiencies of 1,2-dichlorobenzene on the catalyst of 25%-CuO@CeO2 were 64.5%, 94.4%, 98.9% at 100, 150 and 200 oC, respectively. The catalyst also showed high stability, and the degradation efficiencies of 1,2-dichlorobenzene on the catalyst activated by calcination still reached more than 90% at 150 oC after six cycles of reuse. The catalytic material exhibited certain oxidation activity and water resistance. When the oxygen content was less than 20% or the water content was less than 15%, the degradation efficiencies of 1,2-dichlorobenzene on 25%-CuO@CeO2 could be maintained above 90%.
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Key words:
- Ce-BTC /
- 1,2-dichlorobenzene /
- CuO@CeO2 /
- catalytic degradation /
- VOC
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表 1 制备所得催化材料的孔结构数据
Table 1. Pore structure data of prepared catalysts
催化材料
Catalysts比表面积/(m2·g−1)
Specific surface area总孔容/(cm3·g−1)
Total pore volume平均孔径/nm
Average pore sizeCeO2 19.1 0.079 2.77 25%-CuO@CeO2 18.8 0.063 4.54 62%-CuO@CeO2 1.99 0.008 2.77 CuO 0.342 0.001 2.65 -
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