Repository logo
 

Time-Resolved IR Spectroscopy Reveals a Mechanism with TiO2 as a Reversible Electron Acceptor in a TiO2 - Re Catalyst CO2 Photoreduction System

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Abdellah, M 
El-Zohry, AM 
Antila, LJ 
Windle, CD 

Abstract

Attaching the phosphonated molecular catalyst [ReIBr(bpy)(CO)₃]⁰ to the wide-band gap semiconductor TiO₂ strongly enhances the rate of visible-light driven reduction of CO₂ to CO in dimethyl formamide (DMF) with triethanolamine (TEOA) as sacrificial electron donor. Herein, we show by transient mid-IR spectroscopy that the mechanism of catalyst photoreduction is initiated by ultrafast electron injection into TiO₂, followed by rapid (ps-ns) and sequential two-electron oxidation of TEOA that is coordinated to the Re center. The injected electrons can be stored in the conduction band (CB) of TiO₂ on a ms-s time scale, and we propose they lead to further reduction of the Re-catalyst and completion of the catalytic cycle. Thus, the excited Re catalyst gives away one electron and would eventually get three electrons back. The function of an electron reservoir would represent a role for TiO₂ in photo-catalytic CO₂ reduction that has previously not been considered. We propose that the increase in photocatalytic activity upon heterogenisation of the catalyst to TiO₂ is due to the slow charge recombination and the high oxidative power of the ReII species after electron injection, as compared to the excited MLCT state of the unbound Re catalyst or when immobilized on ZrO₂, which results in a more efficient reaction with TEOA.

Description

Keywords

40 Engineering, 34 Chemical Sciences, 4018 Nanotechnology, 3406 Physical Chemistry

Journal Title

Journal of the American Chemical Society

Conference Name

Journal ISSN

0002-7863
1520-5126

Volume Title

139

Publisher

American Chemical Society
Sponsorship
Christian Doppler Forschungsgesellschaft (unknown)
Knut and Alice Wallenberg Foundation, Swedish Energy Agency, Swedish Research Council, Austrian Christian Doppler Research Association, OMV Group