与汽油发动机相比,柴油发动机具有热效率高、CO2排放低、寿命长、续航距离远和经济性好等优点,可大大缓解能源短缺,降低 CO2排放量.因此,机动车柴油化是当前发展趋势.然而,柴油发动机在使用过程中会排放大量炭烟颗粒物,对人体危害极大.因此,控制炭烟颗粒排放成为环境催化研究的重点之一.
炭烟颗粒物催化燃烧反应是典型的固(炭烟颗粒)-固(催化剂)-气(O2)多相催化反应.三维有序大孔氧化物(3DOM)具有大孔径和内部贯通的孔道结构,能有效提高炭烟颗粒与催化活性中心的接触性能.同时,纳米 Au颗粒在大孔氧化物表面的负载可有效提高催化剂本征活性,但纳米 Au颗粒催化剂热稳定性较差. CeO2具有较好的储放氧性能,可与贵金属活性组分发生相互作用,从而提高贵金属纳米颗粒的分散度和稳定性.因此,本文从柴油炭烟颗粒物催化燃烧反应本质出发,设计制备了高炭烟燃烧催化活性的3DOM氧化物担载 Au基催化剂,研究了 Au与 CeO2强相互作用对炭烟燃烧活性的影响.
采用胶体晶体模板法制备3DOM Al2O3载体,由微孔膜氨沉淀法制备 CeO2/3DOM Al2O3催化剂,以还原-沉积法制备 Au/3DOM Al2O3和 Au/CeO2/3DOM Al2O3催化剂,并利用扫描电镜、N2物理吸附-脱附、X射线衍射、透射电镜、紫外漫反射光谱、H2程序升温还原和 X射线光电子能谱等手段对催化剂形貌、比表面积、物理化学性质和氧化还原性进行了表征.结果表明,在 CeO2/3DOM Al2O3中, Al3+可进入到氧化铈晶格内,形成 Al-Ce-O固溶体,产生氧空位,这有利于氧物种转移.此外, Au/CeO2/3DOM Al2O3催化剂中 Au和 CeO2之间的强相互作用能增加 Au纳米颗粒表面活性氧物种数量,从而促进柴油炭烟燃烧反应.纳米颗粒 Au的担载使得催化柴油炭烟燃烧的起燃温度明显降低,其中 Au/CeO2/3DOM Al2O3催化剂表现出最高的催化活性,T10,T50和T90分别为273,364和412oC.
Au/3DOM (three‐dimensionally ordered macroporous) Al2O3 and Au/CeO2/3DOM Al2O3 were pre‐pared using a reduction‐deposition method and characterized using scanning electron microscopy, N2 adsorption‐desorption, X‐ray diffraction, transmission electron microscopy, ultraviolet‐visible spectroscopy, temperature‐programmed hydrogen reduction, and X‐ray photoelectron spectrosco‐py. Au nanoparticles of similar sizes were well dispersed and supported on the inner walls of uni‐form macropores. The norminal Au loading is 2%. Al–Ce–O solid solution in CeO2/3DOM Al2O3 cata‐lysts can be formed due to the incorporation of Al3+ions into the ceria lattice, which causes the crea‐tion of extrinsic oxygen vacancies. The extrinsic oxygen vacancies improved the oxygen‐transport properties. The strong metal–support interactions between Au and CeO2 increased the amount of active oxygen on the Au nanoparticle surfaces, and this promoted soot oxidation. The activities of the Au‐based catalysts were higher than those of the supports (Al2O3 or CeO2/3DOM Al2O3) at low temperature. Au/CeO2/3DOM Al2O3 had the highest catalytic activity for soot combustion, with T10, T50, and T90 values of 273, 364, and 412 °C, respectively.
参考文献
| [1] | Xu, J.;Liu, J.;Zhao, Z.;Xu, C.;Zheng, J.;Duan, A.;Jiang, G..Easy synthesis of three-dimensionally ordered macroporous La _(1-x)K_xCoO_3 catalysts and their high activities for the catalytic combustion of soot[J].Journal of Catalysis,20111(1):1-12. |
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