Revealing OH species in situ generated on low-valence Cu sites for selective carbonyl oxidation.

Autor: Cao Y; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, China., Zhang Q; Department of Civil and Environmental Engineering, National University of Singapore, Singapore 117576, Singapore., Yu IKM; Department of Civil and Environmental Engineering, National University of Singapore, Singapore 117576, Singapore., Tsang DCW; Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong 999077, China.
Jazyk: angličtina
Zdroj: Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2024 Oct 15; Vol. 121 (42), pp. e2408770121. Date of Electronic Publication: 2024 Oct 10.
DOI: 10.1073/pnas.2408770121
Abstrakt: Catalytic oxidation through the transfer of lattice oxygen from metal oxides to reactants, namely the Mars-van Krevelen mechanism, has been widely reported. In this study, we evidence the overlooked oxidation route that features the in situ formation of surface OH species on Cu catalysts and its selective addition to the reactant carbonyl group. We observed that glucose oxidation to gluconic acid in air (21% O 2 ) was favored on low-valence Cu sites according to X-ray spectroscopic analyses. Molecular O 2 was activated in situ on Cu 0 /Cu + forming localized, adsorbed hydroxyl radicals (*OH) which played the primary reactive oxygen species as confirmed by the kinetic isotope effect (KIE) study in D 2 O and in situ Raman experiments. Combined with DFT calculations, we proposed a mechanism of O 2 -to-*OH activation through the *OOH intermediate. The localized *OH exhibited higher selectivity toward glucose oxidation at C1HO to form gluconic acid (up to 91% selectivity), in comparison with free radicals in bulk environment that emerged from thermal, noncatalytic hydrogen peroxide decomposition (40% selectivity). The KIE measurements revealed a lower glucose oxidation rate in D 2 O than in H 2 O, highlighting the role of water (H 2 O/D 2 O) or its derivatives (e.g., *OH/*OD) in the rate-determining step. After proving the C1-H activation step kinetically irrelevant, we proposed the oxidation mechanism that was characterized by the rate-limiting addition of *OH to C1=O in glucose. Our findings advocate that by maneuvering the coverage and activity of surface *OH, high-performance oxidation of carbonyl compounds beyond biomass molecules can be achieved in water and air using nonprecious metal catalysts.
Competing Interests: Competing interests statement:The authors declare no competing interest.
Databáze: MEDLINE
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