Journal Article

High-spatial-resolution mapping of catalytic reactions on single particles

Wu, Chung-Yeh, Wolf, William J., Toste, F. Dean, Gross, Elad, Bechtel, Hans A., Levartovsky, Yehonatan, Martin, Michael C.

2017

Overview

The chemical conversion of N-heterocyclic carbene molecules attached to catalytic particles is monitored at high spatial resolution using synchrotron-radiation-based infrared nanospectroscopy. Catalytic reactivity of single platinum nanoparticles By mapping the catalytic reactivity of single nanoparticles, it is possible to directly reveal structure–reactivity correlations at the nanoscale. Now Dean Toste, Elad Gross and colleagues address this goal through detailed high-spatial-resolution spectral imaging of catalytic reactions on the surface of single platinum nanoparticles. The authors attach stable molecules carrying a functional chemical group to catalyst particles, and monitor the conversion of the functional group by using near-field infrared spectroscopy with synchrotron light. The approach shows that, compared with flat regions on the top of the particles, their peripheries — which contain metal atoms with low coordination numbers — are more active in catalysing oxidation and reduction reactions. The critical role in surface reactions and heterogeneous catalysis of metal atoms with low coordination numbers, such as found at atomic steps and surface defects, is firmly established 1 , 2 . But despite the growing availability of tools that enable detailed in situ characterization 3 , so far it has not been possible to document this role directly. Surface properties can be mapped with high spatial resolution, and catalytic conversion can be tracked with a clear chemical signature; however, the combination of the two, which would enable high-spatial-resolution detection of reactions on catalytic surfaces, has rarely been achieved. Single-molecule fluorescence spectroscopy has been used to image and characterize single turnover sites at catalytic surfaces 4 , 5 , but is restricted to reactions that generate highly fluorescing product molecules. Herein the chemical conversion of N-heterocyclic carbene molecules attached to catalytic particles is mapped using synchrotron-radiation-based infrared nanospectroscopy 6 , 7 with a spatial resolution of 25 nanometres, which enabled particle regions that differ in reactivity to be distinguished. These observations demonstrate that, compared to the flat regions on top of the particles, the peripheries of the particles—which contain metal atoms with low coordination numbers—are more active in catalysing oxidation and reduction of chemically active groups in surface-anchored N-heterocyclic carbene molecules.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/638/542/971 / 639/638/77/885 / 639/638/77/887 / Atoms & subatomic particles / Catalysis / Catalysts / Chemical reactions / Humanities and Social Sciences / INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY / letter / Microscopy / multidisciplinary / Observations / Particle dynamics / Science