Advanced Characterizations


Spectroscopy

Aberration-corrected scanning transmission electron microscope JEOL ARM 200F
The NUS aberration-corrected scanning transmission electron microscope is equipped with an advanced ASCOR corrector allowing it to form atomic-scale probes at accelerating voltages as low as 40 kV, making it possible to see single heavy atoms dispersed in a light support by Z-contrast imaging. Furthermore, it is possible to perform simultaneous electron energy loss spectroscopy for elemental identification, and in the case of transition metals, direct determination of valence, and any bonding to light elements such as oxygen. Coupled with density functional theory, it is possible to determine the coordination and electronic structure of the active sites, and therefore to understand the origin of activity and selectivity. In addition to such studies in vacuum, an environmental cell is planned, capable of allowing imaging at atomic resolution under actual reaction conditions. Samples will be held at temperature, in a gaseous environment at controlled temperature and pressure, and outgoing reaction products will be passed through a mass spectrometer to correlate changes in morphology, composition and structure as a function of reaction conditions.


In-situ XPS spectroscopy
One of the key research focuses of Professor Chen Wei’s group is the “Interface-controlled nanocatalysis for energy and environmental research, with particular emphasis on the CO2 utilization and conversion”. By using the state-of-art near-ambient-pressure x-ray photoelectron spectroscopy and synchrotron-based x-ray absorption techniques, we will study the catalyst reaction mechanism at the real time, thereby providing the design principles to design more efficient heterogeneous catalyst for CO2 conversion. We will also investigate surface reaction mechanism at the atomic scale using model catalyst and low-temperature scanning tunneling microscopy.

Publications
[1] H.B. Yang, S.F. Hung, S. Liu, K. Yuan, S. Miao, L. Zhang, X. Huang, H.Y. Wang, W. Cai, R. Chen, and J. Gao. "Atomically dispersed Ni(i) as the active site for electrochemical CO2 reduction." Nature Energy 3 (2018): 140.
[2] K. Yuan, J.Q. Zhong, S. Sun, Y. Ren, J.L. Zhang, and W. Chen. "Reactive Intermediates or Inert Graphene? Temperature-and Pressure-Determined Evolution of Carbon in the CH4–Ni (111) System." ACS Catalysis 7 (2017): 6028.
[3] K. Yuan, J.Q. Zhong, X. Zhou, L. Xu, S.L. Bergman, K. Wu, G.Q. Xu, S.L. Bernasek, H.X. Li, and W. Chen. "Dynamic oxygen on surface: catalytic intermediate and coking barrier in the modeled CO2 reforming of CH4 on Ni (111)." ACS Catalysis 6 (2016): 4330.
[4] F. Wang, L. Xu, J. Zhang, Y. Zhao, H. Li, H.X. Li, K. Wu, G.Q. Xu, and W. Chen. "Tuning the metal-support interaction in catalysts for highly efficient methane dry reforming reaction." Applied Catalysis B: Environmental 180 (2016): 511.
[5] L. Xu, F. Wang, M. Chen, J. Zhang, K. Yuan, L. Wang, K. Wu, G. Xu, and W. Chen. "CO2 methanation over a Ni based ordered mesoporous catalyst for the production of synthetic natural gas." RSC Advances 6 (2016): 28489.