Oxide nanoparticles are widely used in heterogeneous catalysis. The surface structures of oxide nanoparticles are of particular interest as they can significantly impact the structures of catalyst metals or directly participate in catalytic reactions. Therefore, controlling the surface structures of oxide nanoparticles is a viable way to control catalysis. In this study, we have investigated two categories of synthetic approaches to control the surface structures. The first is to synthesize oxide nanoparticles with different well-defined shapes. In this case, CeO2 nanocubes, nanorods, and nanooctahedra were synthesized via hydrothermal methods. The nanocrystals with different shapes have different facets exposed. For the second approach, we have controlled the atomic surface structures of SrTiO3 nanocuboids to be SrO, TiO2 and mixed SrO/TiO2 terminations while the cuboid shapes are maintained.
The surface structures of both systems were characterized by high resolution transmission electron microscopy (HRTEM) and other techniques at atomic resolution. Carbon monoxide (CO) oxidation was used as a test reaction for the catalytic properties of each system. For the CeO2 system, we determined the atomic structures of (100), (110) and (111) surfaces. The three surfaces have different concentrations of oxygen vacancies, which were believed to be the origin of the distinct catalytic activities of CeO2 nanocrystals in the CO oxidation test. For the SrTiO3 nanocuboids, we have found the (100) surface can be SrO-, TiO2-, and mixed SrO/TiO2-terminated, depending on the synthetic procedures. The SrO and TiO2 terminations result in the shape change of Pt nanoparticles grown on the surfaces. The shape change of Pt nanoparticles leads to the different catalytic activities of CO oxidation.
In this talk, the atomic surface structures the SrTiO3 and CeO2 nanocrystals will be highlighted. The formation mechanisms of the different surface structures and the related catalytic properties will be discussed.
 Y. Lin, J. Wen et al., Phys. Rev. Lett. (2013), 111, 156101.
 Y. Lin, Z. Wu et al., Nano. Lett. (2014), 14, 191.