Confined Mn2+ enables effective aerobic oxidation catalysis

Effective and mild activation of O 2 is essential but challenging for aerobic oxidation. In heterogeneous catalysis, high-valence manganese oxide ( e.g. , +4) is known to be active for the oxidation, whereas divalent MnO is ineffective due to its limited capacity to supply surface oxygen and its the...

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Published in:Science China. Chemistry 2024-05, Vol.67 (5), p.1545-1553
Main Authors: Yuan, Desheng, Ma, Sicong, Kong, Xiao, Zhang, Chi, Chen, Lin, Yang, Chengsheng, Wang, Lihua, Liu, Zhen, Ye, Lin, Liu, Yongmei, Ma, Rui, Liu, Zhi-Pan, Zhu, Yifeng, Cao, Yong, Bao, Xinhe
Format: Article
Language:English
Subjects:
Absorption spectroscopy
Benzyl alcohol
Catalysis
Catalysts
Catalytic activity
Chemistry
Chemistry and Materials Science
Chemistry/Food Science
Communications
Hydroxymethylfurfural
Infrared spectroscopy
Low temperature
Manganese oxides
Oxidation
Photoelectrons
Roasting
Spectrum analysis
X ray absorption
X ray photoelectron spectroscopy
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Summary:Effective and mild activation of O 2 is essential but challenging for aerobic oxidation. In heterogeneous catalysis, high-valence manganese oxide ( e.g. , +4) is known to be active for the oxidation, whereas divalent MnO is ineffective due to its limited capacity to supply surface oxygen and its thermodynamically unstable structure when binding O 2 in reaction conditions. Inspired by natural enzymes that rely on divalent Mn 2+ , we discovered that confining Mn 2+ onto the Mn 2 O 3 surface through a dedicated calcination process creates highly active catalysts for the aerobic oxidation of 5-hydroxymethylfurfural, benzyl alcohol, and CO. The Mn 2 O 3 -confined Mn 2+ is undercoordinated and efficiently mediates O 2 activation, resulting in 2–3 orders of magnitude higher activity than Mn 2 O 3 alone. Through low-temperature infrared spectroscopy, we distinguished low-content Mn 2+ sites at Mn 2 O 3 surface, which are difficult to be differentiated by X-ray photoelectron spectroscopy. The combination of in-situ energy-dispersive X-ray absorption spectroscopy and X-ray diffraction further provides insights into the formation of the newly identified active Mn 2+ sites. By optimizing the calcination step, we were able to increase the catalytic activity threefold further. The finding offers promising frontiers for exploring active oxidation catalysts by utilizing the confinement of Mn 2+ and often-ignored calcination skills.
ISSN:1674-7291
1869-1870
DOI:10.1007/s11426-023-1994-2