Improving Selectivity and Activity of CO2 Reduction Photocatalysts with Oxygen

Stefanie Kreft, Roland Schoch, J. Schneidewind, J. Rabeah, Evgenii V. Kondratenko, Vita A. Kondratenko, Henrik Junge, Matthias Bauer, Sebastian Wohlrab, Matthias Beller

Research output: Contribution to journalArticlepeer-review

71 Scopus citations

Abstract

A highly porous photocatalyst (copper on TiO2 aerogel) was synthesized and applied in aqueous CO2 reduction without using external sacrificial electron donors. For the first time, complete selectivity toward CO and improved catalyst productivity are observed in the presence of oxygen. The optimal activity is achieved in a feed containing 0.5 vol% O2 in CO2. In situ XAS, EPR, and UV-vis measurements suggest, among different Cu oxidation states, Cu(I) to be the most active species in photocatalytic CO2 reduction. Oxygen sensing of the catalyst in the presence of O2/CO2 mixtures indicated an unexpected photoadsorption of oxygen on the titania surface. We propose photooxidation of surface hydroxyl groups to be the electron source for CO2 reduction, which is supported by hydroxyl group consumption, detection of hydroxyl radicals using in situ EPR, and detection of surface peroxide species after the reaction. The consumption of fossil fuels for energy generation results in harmful CO2 emissions, necessitating carbon-neutral energy sources for global environmental sustainability. Instead of releasing CO2 into the atmosphere, using it as a renewable carbon feedstock for the synthesis of valuable chemicals and/or fuels is highly desirable. Photocatalytic CO2 reduction to C1 compounds combines the use of solar energy with CO2 valorization and is of great interest in basic research. Semiconductors, especially TiO2, are commonly used as photocatalysts. In this work, a highly porous TiO2 aerogel was synthesized and applied in aqueous CO2 reduction to CO. Thereby, improved catalyst productivity was observed in the presence of oxygen. Furthermore, progress in understanding the lesser known and challenging oxidation process has been achieved.

Original languageEnglish
Pages (from-to)1818-1833
Number of pages16
JournalChem
Volume5
Issue number7
DOIs
StatePublished - 11 Jul 2019
Externally publishedYes

Keywords

  • CO reduction
  • SDG7: Affordable and clean energy
  • TiO
  • photocatalysis
  • presence of oxygen
  • selective

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