Academic Affiliation: Department of Chemistry and London Centre for Nanotechnology, University College London

Talk: October 15, 2018

Microscopic Investigation on Elements of Model Catalyst Systems

Understanding heterogeneous catalysis has been one of the most long-standing aim and achievement in the field of modern surface science. Development of scanning probe microscopy technique opened a new perspective for understanding of heterogeneous catalysis, by not only providing local structural information in atomic- and molecular resolution, but also enabling local manipulation and excitation.

In this talk, microscopic investigation using low-temperature scanning tunneling microscopy on elements of heterogeneous catalysis – namely reactants (adsorbates), metal catalyst, and oxide support – is presented, which reveals interesting local aspects only possible in atomic- and molecular resolution.

The first part deals with the interaction between adsorbates and metal catalyst, by employing CO chemisorbed on Pt(111) surface, with a range of adsorbate coverage. Overlayer structures of CO on Pt(111) changes from randomly scattered molecules to ontop-dominant (√3 ×√3)R30° islands, gradual occupation of bridge-site with a specific geometry, eventually leading to the formation of c(4×2) domains.[1] The island structures and laterally confined shuttling of a single bridgeadsorbed CO molecule in a local unit indicates the relatively long-range intermolecular interaction. STM action spectroscopy (STM-AS) and construction of model potential energy surface considering the intermolecular interaction successfully reveal a metastable state involved to the motion of bridge CO, and its spectroscopic information.[2]

The second part deals with “oxide support”, employing the most abundant oxide system, silicon oxide. Recent exploration of 2D ultra-thin silica films supported on metal surface successfully resolves atomic arrangements, revealing the structural diversity. In addition to known crystalline monolayer, crystalline and amorphous bilayer, new polymorph with zigzag line shape is investigated with STM and other spectroscopic methods, supported with DFT calculation.[3] This particular polymorph is one of ordered intermediate phase of silica ultra-thin film, including 3-membered ring comprised by tetrahedral SiO4 units.

Reference:
[1] H. J. Yang, T. Minato, M. Kawai, and Y. Kim, J. Phys. Chem. C 117, 16429 (2013).
[2] H. J. Yang, M. Trenary, M. Kawai, and Y. Kim, J. Phys. Chem. Lett. 7, 4369 (2016).
[3] D. Kuhness, H. J. Yang, M. Heyde, and H.-J. Freund et al., J. Am. Chem. Soc. 140, 6164 (2018).