Subscriber access provided by Nottingham Trent University
Letter
Intrinsic Relation between Hot Electron Flux and Catalytic Selectivity during Methanol Oxidation Si Woo Lee, Woonghyeon Park, Hyosun Lee, Hee Chan Song, Yousung Jung, and Jeong Young Park ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b02402 • Publication Date (Web): 09 Aug 2019 Downloaded from pubs.acs.org on August 9, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Intrinsic Relation between Hot Electron Flux and Catalytic Selectivity during Methanol Oxidation Si Woo Lee†,‡, Woonghyeon Park§, Hyosun Lee†, Hee Chan Song†,§, Yousung Jung*,§, and Jeong Young Park*,†,‡ †Center
for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
‡Deapartment
of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
§Graduate
School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
ABSTRACT Catalytic selectivity, or the production of only one desired molecule that may be used as a fuel or chemical out of several thermodynamically possible molecules, is the foundation of surface chemistry. During catalytic reactions, electronic excitation taking place on the surface creates energetic electrons called “hot electrons” that have a significant impact on catalytic reactions. Despite its importance in fundamentally understanding electronic excitation on the surface, no reports show the relation between hot electron flow and catalytic selectivity. Here, using a Pt/ntype TiO2 Schottky nanodiode, we show the intrinsic relation between hot electron flow and catalytic selectivity. On the Pt thin film, hot electron flow was generated by methanol oxidation exhibiting a two-path reaction of either full oxidation to CO2 or partial oxidation to methyl formate; a steady-state chemicurrent was detected. We show that the activation energy of the chemicurrent is quite close to that of the turnover frequency, indicating that the chemicurrent originated from the catalytic reaction on the Pt thin film. The dependence of the chemicurrent on methanol partial pressure was investigated by varying the partial pressure of methanol (1– 4 Torr). We show that hot electron generation is more effective in the reaction pathway that produces methyl formate. Based on these results, we conclude that the selectivity for methyl formate production correlates well with hot electron generation because of the higher exothermicity of generating the intermediate, as was confirmed using theoretical calculations based on the density functional theory. KEYWORDS: Hot electron, catalytic nanodiode, chemicurrent, methanol oxidation, selectivity, exothermic energy, chemical energy conversion
ACS Paragon Plus Environment
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 24
*To whom correspondence should be addressed. E-mail:
[email protected],
[email protected] 1. INTRODUCTION Elucidating the electronic excitation processes caused by energy dissipation and conversion by nonadiabatic excitation (electron–hole pairs) or adiabatic processes (phonons) during exothermic chemical reactions on a catalyst surface is essential for understanding the mechanism for charge transfer in heterogeneous catalysis.1-3 Nonadiabatic energy dissipation in exothermic chemical reactions at solid–gas interfaces leads to the flow of energetic electrons with an energy of 1–3 eV, which are called “hot electrons” when chemical energy is converted to a flow of electrons on a femtosecond time scale before atomic vibrations dissipate the energy. It is well known that these energetic electrons play an important role in determining the catalytic activity in various catalytic systems resulting from charge transfer.4-8 Probing charge flows during chemical reactions is crucial to alter the performance of a catalyst. Direct detection of hot electrons is challenging because of the fast extinction of the electrons by thermalization through
