基于石墨烯涂层的纳米Pd整体催化剂及低温催化燃烧VOCs性能

Volatile organic compounds (VOCs) are major air pollutants. Currently, catalytic combustion is one of the most important technologies for eliminating VOCs. It is very significant for this combustion to take place at low temperatures. However, at these conditions, for tranditional noble-metal monolithic catalyst, the water vapour produced may be adsorbed on the oxide washcoat with negative effects on the catalytic activity. To minimize the effect of water, hydrophobic carbon materials, i.e. activated carbon and carbon nanofiber, have been used as supports for catalysts in the total VOC combustion. But it has been found that the 3-D pore structure of these carbon is not propitious for catalyst efficiency because of the diffusion limitations. To tackle this issue, we present herein a strategy for the low-temperature catalytic combustion of VOCs based on graphene washcoat due to its two-demensional structure, high hydrophobicity and strong adsoption of benzene. A new type of VOCs combustion catalysts are developed by the combination of ceramic monoliths, graphene and Pd nanoparticles..PDDA, an ordinary polyelectrolyte, is employed to reduce graphene oxide and modify graphene at the same time; that is, positively charged PDDA acts as both a reducing agent and a good surface modification molecule. The resulting modified-graphene can be uniformly deposited on the negatively charged cordierite surface by electrostatic self-assembly method. Futhermore, PDDA adsorbed on the surface of graphene nanosheets acts as a glue molecule to facilitate the in situ growth of Pd and the uniform distribution of Pd nanoparticles on the graphene surface. PdCl42- ions are first confined in the positively charged PDDA via electrostatic interaction and then reduced to Pd nanoparticles by NaBH4. By this controlled and environmentally friendly approach, the nano-Pd catalyst supported on graphene coated monolith are successfully synthesized..The new graphene-coated monolithic catalyst will be studied in the low-temperature catalytic combustion of benzene, toluene and xylene. Based on the structural characterization, the interaction among the three of graphene, PDDA and Pd nanoparticles will be figured out. Combined with the test of adsoption and catalytic activity for VOCs, we will understand the relationship of structure and catalytic performance, establish the model and clarify the mechanism of synergy..In practice, this type of catalyst is highly valuable for the economic and efficient treatment of VOCs pollution. Besides, this is of great significance to expand the application of graphene in catalytic field.

本研究以低温催化燃烧脱除挥发性有机物（VOCs）为应用背景，针对贵金属整体催化剂氧化物涂层吸水与三维孔碳结构内扩散问题，利用石墨烯高疏水性、二维平面结构、对苯环强吸附及对贵金属颗粒的高分散与锚定作用等独特性能，发展基于石墨烯涂层的高活性纳米Pd整体催化剂。通过聚二烯丙基二甲基氯化铵（PDDA）一步法完成氧化石墨烯到改性石墨烯的转化，利用静电自组装将改性石墨烯均匀稳定沉积于堇青石孔道表面，结合PDDA静电吸附Pd前驱体阴离子，再与硼氢化钠原位还原，实现Pd纳米粒子在石墨烯表面高分散负载，最终实现所构筑催化剂的可控制备。以催化剂结构表征为基础，明确石墨烯、PDDA与Pd纳米粒子之间电子作用，对石墨烯吸附能力与催化剂低温脱除VOCs活性进行评价，揭示构效关系，阐明吸附-催化协同作用规律与机制。这对于扩展石墨烯新材料在催化领域的应用与经济而高效处理VOCs污染具有重要理论意义与实际应用价值。

本项目以低温催化燃烧脱除挥发性有机物（VOCs）为应用背景，利用石墨烯高疏水性、二维平面结构、对苯环强吸附及对贵金属颗粒的高分散与锚定作用等独特性能，发展出了基于石墨烯涂层的高活性纳米Pd整体催化剂，成功实现了VOCs的低温高效脱除。.在优化了改进的Hummers法制备氧化石墨烯（GO）的制备工艺的基础上，对GO进行改性研究。改性过程有助于对GO表面电位的调控，保持石墨烯完整的π-π共轭结构，增加GO表面的活性位点的数量及活性以及获得表面固体酸。.制备出的Pd/石墨烯/堇青石整体式催化剂（Pd/Gr/Cor），与堇青石载体直接负载钯催化剂相比，所负载的Pd粒子粒径明显减小，粒径只有约4-5 nm，催化活性提高了3倍以上。而Pd/PDDA改性石墨烯/堇青石整体式催化剂（Pd/(Gr+PDDA)/Cor），不仅增加了催化剂的活性和稳定性，也显示出了较上述Pd/Gr/Cor更高的活性。对于Pd/NH2-IL改性石墨烯/堇青石整体式催化剂，老化后活性仅下降30%，大大低于活性炭载体的催化剂（老化后活性下降了92%）。.以甲苯为目标污染物评价了Pd/Gr/Cor催化剂对VOCs低温催化燃烧性能。与无石墨烯涂层催化剂相比，Pd/Gr/Cor催化剂对甲苯的起燃温度从180 ℃降至120 ℃。活化能为60.93 kJ/mol，低于文献中报道值（106.1 kJ/mol）。对甲苯的吸附实验结果表明甲苯的苯环与石墨烯的碳环之间的π-π共轭作用。为阐明吸附催化协同作用机理，提供有力的实验依据。.上述研究进展、结果和关键数据的获得，为低温催化燃烧脱除挥发性有机物（VOCs）的高效催化剂的制备，提供了重要的理论和实验基础。对于有机物的催化降解以及减轻空气污染，都具有一定的理论意义和实际应用价值。