Miao, TJ;
Wang, C;
Xiong, L;
Li, X;
Xie, J;
Tang, J;
(2021)
In Situ Investigation of Charge Performance in Anatase TiO2 Powder for Methane Conversion by Vis–NIR Spectroscopy.
ACS Catalysis
, 11
(13)
pp. 8226-8238.
10.1021/acscatal.1c01998.
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Abstract
The intrinsic behavior of photogenerated charges and reactions with chemicals are key for a photocatalytic process. To observe these basic steps is of great importance. Here we present a reliable and robust system to monitor these basic steps in powder photocatalysts, and more importantly to elucidate the key issue in photocatalytic methane conversion over the benchmark catalyst TiO2. Under constant excitation, the absorption signal across the NIR region was demonstrated to be dominated by photoexcited electrons, the absorption of photoexcited holes increases toward shorter wavelengths in the visible region, and the overall shapes of the photoinduced absorption spectra obtained using the system demonstrated in the present work are consistent with widely accepted transient absorption results. Next, in situ measurements provide direct experimental evidence that the initial step of methane activation over TiO2 involves oxidation by photoexcited holes. It is calculated that 90 ± 6% of photoexcited electrons are scavenged by O2 (in dry air), 61 ± 9% of photoexcited holes are scavenged by methane (10% in argon), and a similar amount of photoexcited electrons can be scavenged by O2 even when the O2 concentration is reduced by a factor of 10. The present results suggest that O2 is much more easily activated in comparison to methane over anatase TiO2, which rationalizes the much higher methane/O2 ratio frequently used in practice in comparison to that required stoichiometrically for photocatalytic production of value-added chemicals via methane oxidation with oxygen. In addition, methanol (a preferable product of methane oxidation) is much more readily oxidized than methane over anatase TiO2.
| Type: | Article |
|---|---|
| Title: | In Situ Investigation of Charge Performance in Anatase TiO2 Powder for Methane Conversion by Vis–NIR Spectroscopy |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1021/acscatal.1c01998 |
| Publisher version: | http://dx.doi.org/10.1021/acscatal.1c01998 |
| Language: | English |
| Additional information: | Copyright © 2021 The Authors. Published by American Chemical Society. This is an open access article under the CC BY 4.0 license Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/) |
| Keywords: | methane conversion, photocatalysis, photoexcited charge carriers, photoinduced in situ spectroscopy, anatase TiO2 |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10130386 |
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