PdM (M = Co, Fe, Mn)双金属纳米晶的可控制备及催化挥发性有机物氧化性能研究

Volatile organic compound (VOC) is one of the key precursors of fine particulate matter (PM2.5) and atmospheric ozone (O3), and is harmful to the human health. Catalytic oxidation is one of the most effective pathways to eliminate VOC, in which the catalyst is the key issue. Bimetallic materials, composed of two distinct metal elements, which often show synergistic effects and collective effects that are distinct from those of their parent metals, offer the opportunity to obtain new catalysts with enhanced catalytic performance. Incorporating abundant metals into noble metals is an effective pathway to developing active and cheap catalysts. However, it is lack of systematic study on understanding the relationship between the structure of bimetallic nanocrystals and catalytic performance of VOC oxidation as well as exploring the chemical nature. In this proposal, we shall adopt the solution-based co-reduction strategy to prepare monodisperse Pd1-xMx (M = Co, Fe, Mn) nanocrystals, and investigate the effect of the preparation conditions on the physicochemical properties of the as-obtained catalyst. The catalytic performance of supported Pd1-xMx (M = Co, Fe, Mn) samples will be evaluated for the complete oxidation of VOC. Based on the results of various characterizations, we can elucidate the “structure-performance” relationship, clarify the involved catalytic mechanisms, and establish the corresponding catalytic reaction kinetic models. It is envisioned that the results obtained in the proposed project will provide a useful guidance on designing novel catalytic materials with high performance and developing the relevant catalytic technologies, and also provide support for air pollution prevention in china.

挥发性有机物（VOC）是形成细颗粒物PM2.5和臭氧（O3）的重要前体物，同时直接危害人身健康。催化氧化法是消除VOC的有效途径，催化剂是实现这一过程的核心。双金属材料结构多样，拥有独特的集合效应和协同效应，在催化领域常显示出优于单一金属的催化性能。利用储量丰富的贱金属部分替代贵金属组成双金属催化材料是开发廉价高效催化剂的有效路径。但目前仍缺乏双金属组成与结构关联VOC催化氧化性能的系统研究和化学本质认识。本课题拟以Pd1-xMx (M = Co, Fe, Mn)双金属纳米晶为研究对象，以明确构效关系和筛选高性能催化剂为研究目的，重点围绕具有不同原子比例合金纳米晶的可控合成和其对典型VOC（苯系物）催化氧化的性能展开系统研究，探明双金属纳米晶催化VOC氧化的作用机制，建立反应动力学模型。研究结果可为新型高效催化材料设计和相关催化技术建立提供有益指导，为大气污染防治提供重要的科技支持。

经过研究纳米双金属催化剂的可控制备、表征及其对典型挥发性有机物（VOC）氧化反应的催化性能，得到如下研究成果：（1）以Pd5Ga3金属间化合物纳米晶为前驱体制备了Pd‒GaOx/Al2O3催化剂，该催化剂比单钯负载型催化剂对于甲烷氧化反应表现出更优异的催化性能（T90%为397oC）。特别是经过水热750oC老化8小时后，Pd‒GaOx双金属催化剂上甲烷氧化T90%为432oC，相比于单Pd负载型催化剂（T90%为522oC），显示出优异的水热稳定性。这与双金属相互作用形成的较高的表面吸附氧物种浓度、较稳定的氧化钯物种和氧化钯与氧化镓之间的强相互作用有关；（2）采用液相还原法，合成了具有二维结构的超薄PdW双金属纳米片，并以TiO2为载体，负载纳米合金得到PdW双金属催化剂。其对于苯氧化的催化活性（T90%为200oC）优于单Pd负载型催化剂。且相比较Pd/TiO2催化剂显示了优异的抗水中毒性能。这与双金属催化剂拥有更好的低温氧化还原性，存在Pd2+/Pd0优化比例以及Pd(O)x‒WOx紧密结合的几何构型有关；（3）采用乙二醇还原法制备粒径为2 nm左右的Pt纳米粒子，再将Pt粒子分散到硝酸亚锰溶液中，将之浸入到聚甲基丙烯酸甲酯微球胶晶模板中，经过滤、干燥和焙烧后制得Pt部分嵌入的3DOM Mn2O3催化剂xwt% Pt/3DOM Mn2O3 (x = 0.2,0.5,1.6,2.3)。其中2.3Pt/3DOM Mn2O3的催化活性最好，与由浸渍法制得的2.0Pt/3DOM Mn2O3-imp相接近（甲苯氧化的T90%为194oC），但是前者经650oC焙烧后的活性与新鲜催化剂的相当，而后者经650 oC焙烧后的活性显著下降。这与呈高分散态嵌入Pt纳米粒子与载体之间的强相互作用有关。（4）采用聚乙烯醇保护的NaBH4还原法制备了一系列xAuPdy/3DOM CeO2催化剂。其中2.85AuPd1.87/3DOM CeO2样品在空速为20,000 mL/(g h) 的反应条件下，具有最好的催化活性（T90% = 415oC）。此外，3DOM CeO2负载AuPd合金催化剂表现出更好的抗氯、抗水中毒性能。这可被归结于Au原子和Pd原子、AuPd合金和载体3DOM CeO2之间存在的强相互作用以及表面酸性和高浓度表面吸附氧的协同作用。