石墨烯限域下的奇异界面化学及催化反应研究

Carbon nanotubes have 1-dimensional (1D) hollow structures and, thus, can be used as nanoreactors for many reactions. Due to the small size (tens of nm) of the hollow space and unique electronic structure of the graphene walls, enhanced catalytic performance may be observed for reactions occurring inside of the carbon nanotubes. It is known that 2D nanospace forms between graphene overlayers and substrates. We have observed that metal atoms or gaseous molecules can be accommodated in the 2D space via an intercalation process. The distance between graphene and substrate typically falls within 1 nm and, moreover, graphene has unique electronic structure at Fermi level. It is expected that adsorbates confined underneath graphene may present novel physical and chemical properties, which, however, have not yet been addressed. In the present project, epitaxial graphene structures are to be grown on metals via chemical vapor deposition (CVD) or surface segregation to obtain the model surfaces, e.g. graphene/Ru(0001), graphene/Pt(111), and graphene/Co(0001). Intercalation of metal atoms and gaseous molecules at the graphene/metal interfaces will be studied by various surface techniques including STM, XPS, UPS, PEEM, and LEEM. The surface reactions occurring at the graphene/metal interfaces can be monitored in-situ by UPS or PEEM. Based on the in-situ and dynamic surface studies, the confinement effect of the graphene "blanket" on the surface chemistry and reactions below will be derived. Furthermore, the basic understanding from the model systems will be extended to the real catalytic systems. Metal@graphene "core-shell" nanoparticles will be synthesized by deposition of monolayer carbon structures on metal nanoparticles. Alternatively, metal or metal oxide nanoparticles can be intercalated into graphite microcrystals, producing graphene/metal/graphene "sandwich" structures. The atomic structure and electronic properties of the graphene-covered or graphene-confined catalysts will be studied by TEM, EELS, XAS, and UPS. Catalytic reactions at gas-solid interfaces, e.g. low temperature catalytic oxidation, ammonia synthesis, and oxygen reduction reaction are conducted over the graphene confined catalysts, which is monitored by gas chromatography (GC) and mass spectrometer (MS). Through the research efforts from both model systems and real catalysts, we attempt to explore the chemistry under graphene. It is expected to see that surface reactions can be controlled by making use of confinement effect of the graphene cover.

石墨烯与固体表面通过弱的范德华力相互作用，因此石墨烯与载体表面形成一个独特的两维纳米空间。前期研究发现通过插层反应单分散的金属催化剂和气体分子可以容纳到石墨烯表面下，从而实现限域在该纳米空间中的催化反应过程。由于石墨烯"毯子"的限域作用，其表面下的化学和催化反应将表现出奇异的行为，这为催化调控提供了新途径。本项目拟在外延石墨烯表面上利用原位动态表征技术从微观上研究石墨烯限域下的表面化学过程，探讨石墨烯对界面处的催化反应的调控机制；进一步合成具有金属@石墨烯"核-壳"结构和石墨烯/金属/石墨烯"三明治"结构的实际纳米催化体系，实现在低温选择氧化、合成氨、电化学氧还原等反应中的应用。在多相催化的研究和实践中，金属表面积碳一直被认为是催化失活的主要原因之一，通过对单层碳限域下的表面催化过程进行深入研究，期望将表面碳结构的形成作为促进催化反应的新途径，重新认识表面碳在多相催化中的作用。

石墨烯等两维材料与固体表面通过弱的范德华力相互作用，因此石墨烯与固体表面形成一个独特的两维纳米空间，通过插层反应单分散金属催化剂和反应气体分子可以容纳到石墨烯表面下，从而实现限域在两维纳米空间中的催化反应过程。借助于石墨烯的限域作用，其表面下的化学和催化反应将表现出奇异的行为，这为催化反应调控开辟了新途径。本项目在石墨烯和h-BN等两维材料表面上利用PEEM/LEEM, STM, NAP-XPS等原位动态表征技术从微观上研究两维限域表面化学过程，探讨表面化学和表面催化的调控机制；制备出具有金属@两维材料“核-壳”结构的纳米催化体系，实现高效催化氧化、合成气转化和电催化反应过程。基于以上的研究从微观上理解两维限域催化效应，提出“限域场”的概念，创制了多种具有高活性和高稳定性的纳米金属催化剂，在合成气转化和电催化反应等过程取得重要应用。在PNAS, Nano Lett, ACS Nano, ACS Catal, Chem Sci等高水平期刊上发表高水平论文22篇。相关研究引起国际同行的广泛关注，受邀在Chemical Society Review上撰写相关专题的综述，着重阐述我们提出的“Chemistry under 2D Cover”概念。同时申请专利5项，在国际会议上做邀请报告8次，培养学生4名。