摘要
甲醛(HCHO)是一种典型的挥发性有机化合物(VOCs).空气中的甲醛主要来源于建筑材料、塑料、水泥和油漆等,长时间暴露于含有甲醛的空气中会对人体健康造成严重危害.因此,消除空气中的甲醛是亟待解决的问题.催化氧化是目前较好的去除甲醛的技术方法之一,它能有效地在较低温度下将甲醛氧化成CO2和H2O.通常,负载型贵金属(Au, Pt, Pd和Ag)催化剂具有较好的催化氧化甲醛性能,但高成本和易中毒的特性限制了其应用.负载型过渡金属催化剂具有成本低和催化氧化性能良好等特点,是当前研究的热点.而催化剂活性通常与所用载体及其物理性质相关,如晶体结构、化学组成、表面积和热稳定性等.因此,开发合适的载体,提高过渡金属催化剂的催化性能具有重要意义.海泡石是具有特定官能团和纤维状结构的天然粘土矿物,相比其他类型的硅酸盐粘土,其具有较高的吸附性能和较好的水热稳定性.本文通过浸渍法制备了钠化海泡石(Na Sep)负载过渡金属催化剂TM/Na Sep (TM=Cu, Fe, Ni, Mn, Co),研究了其物理化学性质,考察了其催化氧化甲醛(0.2%)性能.XRD与SEM结果表明,负载过渡金属不影响海泡石原矿的物理结构.H2-TPR, NH3-TPD和XPS结果表明,负载过渡金属对催化剂氧化还原性能、酸性和吸附氧能力影响较大.TM/NaSep总酸度与吸附氧能力(Oads/(Olatt+OOH))按以下顺序递减:Cu/Na Sep>Fe/NaSep>Mn/NaSep>Ni/NaSep>Co/NaSep.这与催化剂催化氧化甲醛活性顺序一致.在所有样品中,Cu/NaSep表现出最佳的催化氧化甲醛活性,在100°C (GHSV=240000 m L/(g·h))可以完全氧化甲醛.42 h稳定性测试表明其具有良好的稳定性.综合研究表明, Cu/NaSep催化剂优良的催化活性与其良好的低温还原性、较高的酸度和吸附氧能力等因素有关.原位DRIFTS研究Cu/NaSep催化剂催化氧化甲醛机理表明,首先,甲醛吸附在催化剂表面,然后表面的吸附氧物种将其氧化成亚甲二氧基(DOM)并迅速转化为甲酸盐物种.同时, Cu/NaSep催化剂较高的催化氧化性能还与海泡石载体的羟基与吸附氧的协同作用有关,海泡石的羟基可以促进甲醛在样品表面吸附,有利于甲酸盐形成,甲酸盐再进一步氧化生成碳酸盐,最终氧化生成CO2和H2O.
Sodium-treated sepiolite(Na Sep)-supported transition metal catalysts(TM/Na Sep;TM = Cu, Fe, Ni, Mn, and Co) were synthesized via a rotary evaporation method. Physicochemical properties of the as-synthesized samples were characterized by means of various techniques, and their catalytic activities for HCHO(0.2%) oxidation were evaluated. Among the samples, Cu/Na Sep exhibited superior performance, and complete HCHO conversion was achieved at 100 ℃(GHSV = 240000 m L/(g·h)). Additionally, the sample retained good catalytic activity during a 42 h stability test. A number of factors, including elevated acidity, the abundance of oxygen species, and favorable low-temperature reducibility, were responsible for the excellent catalytic activity of Cu/Na Sep. According to the results of the in-situ DRIFTS characterization, the HCHO oxidation mechanism was as follows:(i) HCHO was rapidly decomposed into dioxymethylene(DOM) species on the Cu/Na Sep surface;(ii) DOM was then immediately converted to formate species;(iii) the resultant formate species were further oxidized to carbonates;(iv) the carbonate species were eventually converted to CO2 and H2O.
作者
董宁
叶青
陈梦月
程水源
康天放
戴洪兴
Ning Dong;Qing Ye;Mengyue Chen;Shuiyuan Cheng;Tianfang Kang;Hongxing Dai(Key Laboratory of Beijing on Regional Air Pollution Control,Department of Environmental Science,College of Environmental and Energy Engineering,Beijing University of Technology,Beijing 100124,China;Beijing Key Laboratory for Green Catalysis and Separation,Key Laboratory of Beijing on Regional Air Pollution Control,and Laboratory of Catalysis Chemistry and Nanoscience,Department of Chemistry and Chemical Engineering,College of Environmental and Energy Engineering,Beijing University of Technology,Beijing 100124,China)
基金
国家自然科学基金(21277008,207770050)
国家重点研发计划(2017YFC0209905)
北京市自然科学基金(8082008).
