纳米金属氧化物可控合成与催化剂组装及其催化性能研究

For nanomaterial, its unique properties are dependent on its structure (size, crystal phase and morphology). While the strong influence of partice size and shape has been successfully demonstrated for metals, this is much less so for metal oxides. One of the reasons for this mismatch is the more complex crystal structure of metal oxides as compared to metals. Especially almost no correlation between the particle size and activity has ever been established before over well-defined transition metal oxides. In the project, a well-defined cobalt oxide catalyst was used to elucidate the structure-reactivity correlation. First of all, the well-defined cobalt oxide nanomaterials with uniform and tunable size were synthesized controllably by tuning the kinetic parameters as well as the addition of surface active agent. Through the study, modulation mechanism was indicated between the nanomaterial structure and synthetic parameters. And The particle-size-derived and particle-morphology-derived structure-reactivity correlations were in operation for the CO and CH4 oxidation reactions over the well-defined cobalt oxide nanomaterials. Then the catalysts were assembled involving Co3O4/carrier, Pd/Co3O4, Pd/Co3O4/Carrier. In combination with the probe reactions, their catalytic performance and promoting effect (metal oxide nanomaterials as a carrier or promoter) were investigated. Meanwhile the dependence of reactivity and promoting effect were determined on the particle size and morphology of well-defined cobalt oxide for CO and CH4 oxidation. These studies on the CO and CH4 oxidation over well-defined cobalt oxide as well as its catalysts may open up new routes in the research for highly active catalysts.

纳米材料独特的物理化学性质依赖于其特殊的结构（尺寸、晶相和形貌）。纳米金属材料形貌和尺寸与其催化性能间的构效关系是催化领域研究的热点，且理论体系日臻完善。而纳米金属氧化物，由于组成和结构的复杂性，相关研究面临较大的挑战，特别是纳米金属氧化物尺寸和催化活性之间的关联性，文献还鲜有报道。本项目以纳米氧化钴为模型催化剂，通过调变合成动力学参数和添加表面活性剂，实现尺寸均一和可控的、具有特定形貌的纳米氧化钴的可控制备，揭示合成动力学参数对纳米材料微观结构的调变机制；结合探针反应，揭示纳米金属氧化物尺寸和形貌与催化性能之间的内在关联；进行纳米材料组装，构建以金属氧化物为载体、活性组分和助剂的催化剂，研究纳米金属氧化物尺寸和形貌与其催化和助催化（金属氧化物纳米材料为载体或助剂）性能之间的构效关系。通过本项目的研究为纳米金属氧化物粒子尺寸和晶面取向优化与功能化利用提供实验和理论指导。

金属氧化物对于氧化还原反应具有高的催化活性和助催化作用，其形貌效应是目前研究的热点，但是关于形貌效应的研究通常是尺寸、形貌、价态以及晶相多个因素的协同耦合催化作用，如何解耦各个因素的影响，揭示内在本质影响是关键。本项目通过单因素多水平的研究理念和催化剂合成路线，剥离了多个因素的影响，并通过甲烷和CO的催化燃烧为模型反应，研究了金属氧化物形貌、尺寸、价态以及晶相对该氧化还原反应的调变，揭示内在的反应机理。通过纳米晶成核和生长动力学研究，调控材料的微观结构，揭示合成条件对纳米金属氧化物粒子微观结构的调控机制，实现了不同形貌（立方体、纳米花、六角片状、六角盘状）、不同尺寸纳米Co3O4的可控合成。系统研究了甲烷、CO在纳米Co3O4上催化燃烧的形貌效应和尺寸效应，阐明了Co3O4形貌与催化性能间的构效关系；考察了相同形貌、不同价态MnOx的臭氧催化分解性能，并通过不同预处理方式对MnOx表面氧缺陷量进行调变，揭示出表面氧缺陷直接影响臭氧分解催化剂的稳定性。为了提高金属氧化物催化剂的稳定性，将纳米金属氧化物组装为钙钛矿ABO3和尖晶石结构AB2O4，研究发现LaMnO3催化剂通过表面柠檬酸刻蚀后，表面残留的MnO2具有更高的催化活性；而A位和B位都是过渡金属氧化物的尖晶石具有更高的催化燃烧活性和稳定性。研究了Pd/不同形貌Co3O4催化剂上CH4、CO催化燃烧反应性能，Pd容易分散在氧缺陷位上，对甲烷催化燃烧具有促进作用；而会抑制CO的催化燃烧；对于CH3Br催化燃烧反应，混相TiO2负载Ru催化剂具有更高的催化燃烧活性；而锐钛矿TiO2负载Ru催化剂具有高的稳定性；而且含氯VOCs和含溴VOCs由于化学硬度的不同，具有不同的催化燃烧行为。通过异质结界面Pdn+-O-Cen+ (Zrn+) 构筑提高了催化剂的还原性和耐硫性能。