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In designing catalysts for clean energy- is the nature of the active site always the right question to ask?

Abstract

One of the greatest challenges of the 21^st century will be securing cheap and renewable sources of energy. One of the most promising approaches to this challenge is to design catalysts from earth-abundant materials capable of implementing key chemical reactions, including splitting water into hydrogen and oxygen (H₂O → 2H⁺ + O₂); and both the oxidation (H₂→ 2H⁺) and reduction (2H⁺→ H₂) of hydrogen among many others. In studying catalysts, we often focus on the “nature of the active site” which for classical heterogeneous catalysts works well- but not all catalysts work by a surface sorption process alone. In some systems, it is increasingly realised that processes of precipitation and reformation may actually be key to catalysis. In this talk we explore the relationship between redox chemistry and catalytic chemistry using birnessite-like manganese oxides and iron sulfides as examples. We argue that structural disorder plays an overlooked role in some catalysts, as it alters thermodynamic stability affecting stability, electron transfer and product selectivity. The redox events between substrate and catalyst and the speed of these processes appear to play a key role in both engineering product selectivity and catalyst stability. Drawing on our in situ XAS work we examine how the events after catalysis may be key for understanding the active events of catalysis as well as mechanisms of decomposition.

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References

¹Kerr B. V., Hocking R. K., et al Energy and Fuels 2022, 36(5) 1258-2389

²Garibello C. F., Hocking R. K. et al, ChemCatChem 2022 14(12) e202200270

³ H. J. King, A. N. Simonov, Hocking R. K., et al.,J. Phys Chem C. 2020, 123(47) 28533-28549