催化学报 ›› 2018, Vol. 39 ›› Issue (4): 606-612.DOI: 10.1016/S1872-2067(17)62939-5

• 快讯 • 上一篇    下一篇

三维有序大孔二氧化钛表面超细钯纳米颗粒的构筑及其增强柴油炭烟催化燃烧性能

韦岳长, 吴强强, 熊靖, 刘坚, 赵震   

  1. 中国石油大学(北京)重质油国家重点实验室, 北京 102249
  • 收稿日期:2017-12-23 修回日期:2018-01-20 出版日期:2018-04-18 发布日期:2018-04-08
  • 通讯作者: 韦岳长, 赵震
  • 基金资助:

    国家自然科学基金(21673142,21477164);国家高技术研究发展计划(863计划,2015AA030903).

Fabrication of ultrafine Pd nanoparticles on 3D ordered macroporous TiO2 for enhanced catalytic activity during diesel soot combustion

Yuechang Wei, Qiangqiang Wu, Jing Xiong, Jian Liu, Zhen Zhao   

  1. State Key Laboratory of Heavy Oil Processing, China University of Petroleum-Beijing, Beijing 102249, China
  • Received:2017-12-23 Revised:2018-01-20 Online:2018-04-18 Published:2018-04-08
  • Contact: 10.1016/S1872-2067(17)62939-5
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21673142, 21477164) and the National High Technology Research and Development Program of China (863 Program, 2015AA030903).

摘要:

柴油机排放颗粒物(主要成分是炭烟)是城市大气PM2.5中一次颗粒物的主要来源和二次颗粒物形成的重要组分,严重危害大气环境和人类健康.利用颗粒物捕集器与催化剂相结合的连续过滤再生技术是满足柴油车国VI炭烟颗粒物排放标准的最有效技术,目前该技术所面临的挑战是研发在排气温度的柴油炭烟颗粒物催化氧化催化剂.柴油炭烟催化燃烧反应的本质是典型的气(氧气)-固(炭烟颗粒)-固(催化剂)三相深度氧化反应,因此我们研究组提出了高活性柴油炭烟燃烧催化剂设计应该遵循优化固-固接触与强化活化分子氧能力二者相结合的研究思路.
为满足此设计思路的要求,本课题组前期采用孔径大于200nm的三维有序大孔(3DOM)结构氧化物作为载体,利用大孔效应来实现PM在催化剂内部的有效扩散,从而提高催化剂与PM的接触效率.采用具有强活化分子氧能力的负载型贵金属(Au,Pt)纳米颗粒或贵金属-氧化物复合纳米颗粒作为活性位来提高催化剂对分子氧的活化能力,进而设计了多个系列高活性催化剂,并形成了担载贵金属纳米颗粒的可控制备方法与装置.然而,Au和Pt昂贵的价格限制了其广泛应用.价格相对便宜的Pd具有与Pt相似的催化性能,是其良好替代品.但是,目前关于3DOM氧化物表面负载型Pd纳米颗粒结构和尺寸与柴油炭烟催化燃烧性能之间的相关研究仍然较少.
基于此,本文采用气泡辅助膜还原法制备了3DOM二氧化钛(TiO2)担载超细Pd纳米颗粒催化剂.利用XRD,Raman,BET,SEM,TEM,ICP,XPS和H2-TPR等技术手段对催化剂进行表征,并以模拟柴油炭烟为研究对象,利用程序升温氧化反应(TPO)对催化剂的活性进行评价,深入探讨了催化剂的制备、结构及物化性质与炭烟催化燃烧反应性能之间的关系.XRD和Raman结果表明,TiO2载体由锐钛矿(主)和金红石(次)两种物相组成.SEM照片显示,所制催化剂为规整的有序大孔结构,球形孔互相贯通,孔径均一,大孔腔平均尺寸为280 nm,孔窗尺寸为109 nm,这种三维有序大孔TiO2的结构能够增强炭烟颗粒与催化剂之间的接触效率.TEM表征显示,平均粒径为1.1 nm的超细半球型Pd纳米颗粒高度分散于TiO2载体的内壁上,两者间的优化界面面积有利于增加活化O2的活性位密度,这些活性位源于Pd与TiO2间强相互作用.H2-TPR和XPS表征印证了上述观点,具有1.1 nm超细Pd颗粒的Pd/3DOM-TiO2催化剂表现出强的低温氧化还原特性和丰富的表面吸附氧物种.在TPO测试中,相对于担载5.0 nm Pd颗粒的催化剂,具有1.1 nm尺寸超细Pd颗粒的Pd/3DOM-TiO2催化剂展示了高的催化炭烟燃烧活性,T10T50T90分别为295,370和415℃,且在5次TPO测试过程中表现出良好的催化和结构稳定性.这种具有3DOM结构和超细Pd纳米颗粒的纳米催化剂能够有效降低Pd的使用量,在催化炭烟燃烧的实际应用中大有潜力.

关键词: 有序大孔材料, 钯, 二氧化钛, 柴油炭烟燃烧, 超细纳米颗粒, 多相催化

Abstract:

Nanocatalysts consisting of three-dimensionally ordered macroporous (3DOM) TiO2-supported ultrafine Pd nanoparticles (Pd/3DOM-TiO2-GBMR) were readily fabricated by gas bubbling-assisted membrane reduction (GBMR) method. These catalysts had a well-defined and highly ordered macroporous nanostructure with an average pore size of 280 nm. In addition, ultrafine hemispherical Pd nanoparticles (NPs) with a mean particle size of 1.1 nm were found to be well dispersed over the surface of the 3DOM-TiO2 support and deposited on the inner walls of the material. The nanostructure of the 3DOM-TiO2 support ensured efficient contact between soot particles and the catalyst. The large interface area between the ultrafine Pd NPs and the TiO2 also increased the density of sites for O2 activation as a result of the strong metal (Pd)-support (TiO2) interaction (SMSI). A Pd/3DOM-TiO2-GBMR catalyst with ultrafine Pd NPs (1.1 nm) exhibited higher catalytic activity during diesel soot combustion compared with that obtained from a specimen having relatively large Pd NPs (5.0 nm). The T10, T50 and T90 values obtained from the former were 295, 370 and 415℃. Both the activity and nanostructure of the Pd/3DOM-TiO2-GBMR catalyst were stable over five replicate soot oxidation trials. These results suggest that nanocatalysts having a 3DOM structure together with ultrafine Pd NPs can decrease the amount of Pd required, and that this approach has potential practical applications in the catalytic combustion of diesel soot particles.

Key words: Ordered macroporous material, Pd, TiO2, Diesel soot combustion, Ultrafine nanoparticle, Heterogeneous catalysis