Catalysis

Catalysis impacts our daily lives from the manufacturing of fertilizer to the catalytic converter on modern cars. An understanding of the behavior of heterogeneous catalysts aide in the development of more robust and selective future generations of catalysts. Many large scale characterization techniques are commonly utilized such as Brunauer-Emmettt-Teller surface area analysis and zeta potential measurements to investigate the material. Conventional methods are an important tool for catalysis measurements but as the field of heterogenous catalysis widened to encompass nanometer and sub-nanometer species, the usage of transmission electron microscopy to directly view these materials has improved our understanding of the static and dynamic behavior of catalysts. With the development of aberration corrected electron microscopes and fast cameras leading to sub-Ångstrom resolution combined with a reasonably high temporal resolution, in situ and ex situ characterization of nanoparticle and single atom catalytic materials at atomic resolution have been achieved.

Our work at UCI focuses on investigating the behavior of nanoparticle and single atom catalysts in situ and ex situ under different stimulus through direct imaging and spectroscopy. Our group uses traditional high resolution HAADF imaging to demonstrate the dispersion and local coordination of single atom catalysts and the morphology of synthesized nanoparticles. Further ex situ characterization of materials is achieved through spectroscopy wherein the elemental composition, distribution, and even the valence state of the catalysts are determined. In situ investigation of the process during different stages such as formation, activity, and degradation of the catalyst provide information about fundamental aspects of the material. We use special TEM holders equipped with a micro-electromechanical system to apply heating, electrical potential, gas, and/or a liquid environment to observe the dynamics of catalysts inside the microscope. Through in situ TEM, we have been able to investigate the preferential behavior of catalysts under reaction conditions.

Related Publications

• Gao, W., Tieu, P., Addiego, C., Ma, Y., Wu, J., Pan, X., Probing the dynamics of nanoparticle formation from a precursor at atomic resolution. Science Advances 2019, 5 (1), eaau9590. https://doi.org/10.1126/sciadv.aau9590
• Dai, S., Chou, J. P., Wang, K. W., Hsu, Y. Y., Hu, A., Pan, X., Chen, T. Y., Platinum-trimer decorated cobalt-palladium core-shell nanocatalyst with promising performance for oxygen reduction reaction. Nature Communications 2019, 10 (1), 440. https://doi.org/10.1038/s41467-019-08323-w
• Dai, S., You, Y., Zhang, S. et al. In situ atomic-scale observation of oxygen-driven core-shell formation in Pt₃Co nanoparticles. Nat Commun 8, 204 (2017). https://doi.org/10.1038/s41467-017-00161-y