Due to the unprecedented intrinsic structural features such as tunable pore sizes, large surface area, flexibility to accommodate various types of functional groups, and capability of anchoring metallic species at defective sites, nanoporous/mesoporous high-surface-area carbon materials have been effectively utilized for liquid phase catalytic transformations of valuable molecules. We have previously developed a synthesis process, via catalytic deposition of carbonaceous species on ZnO nanowires and the subsequent reduction-evaporation of the ZnO nanowire template, to produce mesoporous hollow carbon nanostructures. Atomic resolution electron microscopy images revealed that the synthesized mesoporous carbon is composed of intertwined short segments of graphene sheets with dimensions in the range of 0.3 to 3.0 nm, resulting in highly disordered and defective nanostructures, which can be used to anchor single metal atoms or small metal clusters. Incorporation of noble metal atoms or small clusters into the nanoporous carbons can be facilely accomplished via wet chemistry methods to fabricate single-atom or cluster catalysts. Such nanoporous carbon supported single Pt1/Pd1 atoms and clusters were evaluated for liquid phase selective hydrogenation of 3-nitrostyrene. The turn-over-number (TON) for producing 3-vinylaniline (with selectivity of 80%) on the Pt1/C catalyst is as high as 31,157 /h at 40°C, more than 20 times higher than that of the best catalyst reported in the open literature . The TON for producing 3-ethyl-nitrobenzene (with selectivity of 97%) on the nanoporous carbon supported Pd clusters is as high as 107,040 /h at 40°C, ~ 1000 times higher than that of the best Pd catalysts reported in the open literature . The anchoring of noble metal single atoms onto the defective sites of the nanoporous carbon nanostructures, the catalytic properties of the anchored single metal atoms, and their stability during liquid phase catalytic reactions will be discussed .
1 H. Wei, X. Liu, A. Wang, L. Zhang, B. Qiao, X. Yang, Y. Huang, S. Miao, J. Liu and T. Zhang, Nat. Commun, 2014, 5, 5634.
2 T. Ishida, Y. Onuma, K. Kinjo, A. Hamasaki, H. Ohashi, T. Honma, T. Akita, T. Yokoyama, M. Tokunaga and M. Haruta, Tetrahedron, 2014, 70, 6150-6155.
3 This work was supported by the National Science Foundation under CHE-1465057.