Nanodiode-based hot electrons: Influence on surface chemistry and catalytic reactions
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uction In heterogeneous catalysis, one of the key technologies for increasing the activity and selectivity of a chemical reaction is the use of catalytically active metal nanoparticles (NPs) in combination with a suitable support.1–6 This approach is based on earlier work that revealed significant changes in the activity of fine metal particles when placed on the support of a metal oxide, even though the support itself is inactive for this reaction. Specifically, in the 1960s, Schwab et al. discovered significant changes in the activity of fine metal particles when placed on the support of a metal oxide,7,8 and attributed this effect to the formation of a Schottky barrier at the metal– oxide interface with the subsequent transfer of charge carriers through the barrier, which affects the course of the surface reaction.3,7,9 This effect was also investigated by Boffa et al.10 using rhodium deposited on various reducible oxides. They observed a remarkable 14-fold increase in catalytic activity for CO2 hydrogenation on three different oxides—TiOx, NbOx, and TaOx. The activity was highest at a half monolayer of oxide coverage where the oxide–metal interface area was at a maximum. Later, these phenomena were referred to as
the strong metal–support interaction (SMSI) effect,11 which indicates the enhancement of catalytic activity when Group VIII metal catalysts (including Pt, Pd, Rh, Fe, Ni, and Ir) are supported on reducible oxides such as CeO2, Nb2O5, and TiO2. To understand the electronic origin of the SMSI effect, it is desirable to directly measure the flow of charge between the metal and the oxide. To achieve this goal, metal–oxide catalysts need to be combined with a Schottky diode, and thus, the catalytic nanodiode was developed.1,2 This article considers the main aspects of research aimed at developing methods for studying the transfer of charge carriers through metal–support interfaces under catalytic reaction conditions. First, we review the mechanisms for hot-electron excitation and transport through metal–oxide interfaces. We then show various schemes for detecting hot electrons that are generated during catalytic processes. We provide an overview of the latest results from detecting hot electrons in supported catalysts during chemical reactions at both gas–solid and liquid–solid interfaces. Hot electrons can be generated by photon absorption on the surface, therefore, the photocatalytic
Jeong Young Park, Center for Nanomaterials and Chemical Reactions, Institute for Basic Science; and Department of Chemistry, Korea Advanced Institute of Science and Technology, Republic of Korea; [email protected] Gabor A. Somorjai, University of California, Berkeley, USA; [email protected] doi:10.1557/mrs.2019.295
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• VOLUME 45 • JANUARY 2020 • mrs.org/bulletin 2020 Materials Downloaded MRS fromBULLETIN https://www.cambridge.org/core. Tulane University Libraries, on 11 Jan 2020 at 14:00:33, subject to the Cambridge Core terms of © use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs
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