催化学报 ›› 2019, Vol. 40 ›› Issue (7): 1100-1108.DOI: 10.1016/S1872-2067(18)63203-6

• 论文 • 上一篇    下一篇

(Ce,Cr)xO2/Nb2O5催化氧化1,2-二氯乙烷过程中氧化性中心与酸性中心的协同作用

万杰a,b, 杨鹏a, 郭晓琳a, 周仁贤a   

  1. a 浙江大学催化研究所, 浙江杭州 310028;
    b 常州清大两岸科技发展有限公司, 江苏常州 213022
  • 收稿日期:2018-10-11 修回日期:2018-11-16 出版日期:2019-07-18 发布日期:2019-05-24
  • 通讯作者: 周仁贤
  • 基金资助:

    国家重点研发计划(2016YFC0204300);国家自然科学基金(21477109).

Elimination of 1,2-dichloroethane over (Ce,Cr)xO2/Nb2O5 catalysts: synergistic performance between oxidizing ability and acidity

Jie Wana,b, Peng Yanga, Xiaolin Guoa, Renxian Zhoua   

  1. a Institute of Catalysis, Zhejiang University, Hangzhou 310028, Zhejiang, China;
    b Changzhou Qingda Cross Strait Science & Technology Development Co., LTD, Changzhou 213022, Jiangsu, China
  • Received:2018-10-11 Revised:2018-11-16 Online:2019-07-18 Published:2019-05-24
  • Supported by:

    This work was supported by the National Key R&D Program of China (2016YFC0204300) and the National Natural Science Foundation of China (21477109).

摘要:

含氯易挥发有机物(Cl-VOCs)是一类常见的大气污染物,可对生态环境和人类健康产生严重危害.相比其他治理方法,催化氧化法具有经济、高效的优势,其关键在于开发新型廉价的高性能催化材料.(Ce,Cr)xO2复合氧化物因具有强氧化性而表现出优异的催化性能,但仍需提高HCl选择性.研究表明,同时提高催化剂酸性和氧化性有助于促进Cl-VOCs降解.Nb2O5等固体酸金属氧化物同时具有丰富的表面酸性中心和一定的氧化性,被广泛应用于酸催化和氧化还原反应.将酸性氧化物和(Ce,Cr)xO2进行有效复合,有望同时改善催化剂的酸性质和氧化性,实现对Cl-VOCs的高效消除.
本文选择Nb2O5作为固体酸载体,采用沉积-沉淀法制备了一系列不同质量比例的复合改性y(Ce,Cr)xO2/Nb2O5催化剂,考察了其对1,2-二氯乙烷(DCE)的催化降解性能,并利用XRD、UV-Raman、N2吸脱附、SEM、NH3-TPD和H2-TPR等手段表征了催化剂的结构-织构性质、形貌、表面酸性质以及氧化还原性能.通过优化活性组分组成,调控复合氧化物催化剂的物理化学性质,进一步提高其催化活性和选择性,并深入探讨了复合氧化物之间的相互作用机制以及氧化性中心与酸性中心二者的协同催化效应对Cl-VOCs催化降解性能的影响.
DCE催化降解实验结果显示,随着(Ce,Cr)xO2/Nb2O5质量比(y值)的增加,y(Ce,Cr)xO2/Nb2O5催化剂对DCE的降解活性先增大后减小,生成副产物C2H3Cl的最大浓度逐渐降低,其中0.25(Ce,Cr)xO2/Nb2O5催化剂的本征催化活性最高.
XRD图谱显示,y(Ce,Cr)xO2/Nb2O5复合催化剂上出现了TT相Nb2O5和立方相CeO2的特征峰;当(Ce,Cr)xO2与Nb2O5质量比小于0.25时,(Ce,Cr)xO2在Nb2O5表面高度分散.UV-Raman结果显示,复合催化剂上Nb2O5特征峰与单组分Nb2O5相比明显向低波数偏移,表明Nb2O5和(Ce,Cr)xO2之间存在较强的相互作用.N2吸脱附表征结果显示,y(Ce,Cr)xO2/Nb2O5为介孔结构,其织构性质变化与催化活性之间无直接联系.SEM照片显示,对于复合催化剂,(Ce,Cr)xO2颗粒高度分散在片状Nb2O5表面,二者的适当复合有利于其紧密接触并增强相互作用,进而充分发挥协同催化效应.
NH3-TPD结果显示,单组分Nb2O5具有最多的强酸中心数量和较高的酸强度,随着(Ce,Cr)xO2含量增加,强酸和总酸中心数量以及强/弱酸中心数量比值均逐渐减小.H2-TPR结果显示,Nb2O5的氧化能力明显弱于(Ce,Cr)xO2,随着质量比y值增大,Nb2O5的δ峰向低温方向移动,并与(Ce,Cr)xO2的γ峰发生重叠,表明在两者界面处存在Nbm+-O-Cen+强相互作用,γ+δ峰的峰面积呈先增大后减小的变化趋势,其中0.25(Ce,Cr)xO2/Nb2O5的γ+δ峰面积最大.此外,复合催化剂中Cr6+物种的α峰面积逐渐增加,表明强氧化性的Cr6+物种含量逐渐增大.酸性中心与氧化中心各自单一方向的变化趋势与催化降解性能先增后减的变化趋势并不一致,表明二者之间的协同催化效应起着重要作用.
综上,与单组分(Ce,Cr)xO2和Nb2O5相比,y(Ce,Cr)xO2/Nb2O5催化剂对DCE的本征催化降解活性显著提高,0.25(Ce,Cr)xO2/Nb2O5催化剂显示出最佳性能.催化剂酸性中心与氧化中心之间存在显著的协同催化效应:酸性中心有利于DCE的吸附和活化以及C-Cl键断裂得到质子化C2H3Cl;氧化中心则有利于C2H3Cl的深度氧化.合适的(Ce,Cr)xO2/Nb2O5比有利于(Ce,Cr)xO2颗粒在Nb2O5表面高度分散,促进酸性中心与氧化中心之间的协同催化效应,从而显著提高(Ce,Cr)xO2/Nb2O5复合催化剂的催化降解性能.

关键词: 1,2-二氯乙烷, 深度氧化, 复合氧化物, 五氧化二铌, 协同催化效应

Abstract:

A series of (Ce,Cr)xO2/Nb2O5 catalysts with different (Ce,Cr)xO2 to Nb2O5 mass ratios were synthesized by the deposition-precipitation method for use in deep catalytic oxidation of 1,2-dichloroethane (DCE), which is one of the typical chlorinated volatile organic compound pollutants. The textural properties were characterized by X-ray diffraction, N2 adsorption/desorption isotherms, UV-Raman spectroscopy, and scanning electron microscopy. The surface acidity and the redox properties were characterized by ammonia temperature-programmed desorption and H2 temperature-programmed reduction, respectively. The results show that the addition of a proper amount of (Ce,Cr)xO2 over Nb2O5 significantly improves the intrinsic catalytic activity towards the deep oxidation of DCE, and only a very small amount of C2H3Cl is detected as the byproduct of the oxidation process. Further study reveals the existence of an obvious synergistic effect between Nb2O5, with abundant strong acid sites, and (Ce,Cr)xO2, with strong oxidation sites, as the strong acid sites of Nb2O5 promote the adsorption and dehydrochlorination of DCE, while the strong oxidation sites of (Ce,Cr)xO2 contribute to the deep oxidation of the reactant, intermediates, and byproducts.

Key words: 1,2-dichloroethane, Deep oxidation, Mixed oxide, Nb2O5, Synergistic effect