Understanding the Reducibility of CeO2 Surfaces by Proton-Electron Transfer from CpCr(CO)3H

Osman Bunjaku; Jan Florenski; Jonathan Wischnat; Elias Klemm; Olga V Safonova; Joris van Slageren; Deven P Estes

doi:10.1021/acs.inorgchem.4c01199

Understanding the Reducibility of CeO₂ Surfaces by Proton-Electron Transfer from CpCr(CO)₃H

Inorg Chem. 2024 Apr 22;63(16):7512-7519. doi: 10.1021/acs.inorgchem.4c01199. Epub 2024 Apr 10.

Authors

Osman Bunjaku¹, Jan Florenski¹, Jonathan Wischnat², Elias Klemm¹, Olga V Safonova³, Joris van Slageren², Deven P Estes¹

Affiliations

¹ Institute of Technical Chemistry, University of Stuttgart, Pfaffenwaldring 55, DE-70569 Stuttgart, Germany.
² Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, DE-70569 Stuttgart, Germany.
³ Paul Scherrer Institut, Forschungsstrasse 111, CH-5232 Villigen, Switzerland.

PMID: 38598679
DOI: 10.1021/acs.inorgchem.4c01199

Abstract

CeO₂ is a popular material in heterogeneous catalysis, molecular sensors, and electronics and owes many of its special properties to the redox activity of Ce, present as both Ce³⁺ and Ce⁴⁺. However, the reduction of CeO₂ with H₂ (thought to occur through proton-electron transfer (PET) giving Ce³⁺ and new OH bonds) is poorly understood due to the high reduction temperatures necessary and the ill-defined nature of the hydrogen atom sources typically used. We have previously shown that transition-metal hydrides with weak M-H bonds react with reducible metal oxides at room temperature by PET. Here, we show that CpCr(CO)₃H (1) transfers protons and electrons to CeO₂ due to its weak Cr-H bond. We can titrate CeO₂ with 1 and measure not only the number of surface Ce³⁺ sites formed (in agreement with X-ray absorption spectroscopy) but also the lower limit of the hydrogen atom adsorption free energy (HAFE). The results match the extent of reduction achieved from H₂ treatment and hydrogen spillover on CeO₂ in a wide range of applications.