Unsaturated Penta-Coordinated Mo5c5+ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers

Qi Yang; Xiujuan Gao; Faen Song; Xiaoxing Wang; Tao Zhang; Pan Xiong; Yunxing Bai; Xingchen Liu; Xiaoyan Liu; Junfeng Zhang; Gang Fu; Yisheng Tan; Yizhuo Han; Qingde Zhang

doi:10.1021/jacsau.3c00479

Unsaturated Penta-Coordinated Mo_5c⁵⁺ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers

JACS Au. 2023 Oct 19;3(11):3141-3154. doi: 10.1021/jacsau.3c00479. eCollection 2023 Nov 27.

Authors

Qi Yang^{1

2}, Xiujuan Gao^{1

2}, Faen Song¹, Xiaoxing Wang¹, Tao Zhang¹, Pan Xiong^{1

2}, Yunxing Bai^{1

2}, Xingchen Liu¹, Xiaoyan Liu³, Junfeng Zhang¹, Gang Fu⁴, Yisheng Tan¹, Yizhuo Han¹, Qingde Zhang^{1

5}

Affiliations

¹ State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China.
² University of Chinese Academy of Sciences, Beijing 100049, China.
³ Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, China.
⁴ State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, China.
⁵ Dalian National Laboratory for Clean Energy, Dalian 116023, China.

Abstract

Selective oxidation of C-H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo⁵⁺ species are effective for these reactions, but the accurate identification of the structure of active Mo⁵⁺ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo_5c⁵⁺ with a high fraction in MoO_x fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo_5c⁵⁺ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C-H bond in CH₃O* at lower temperatures.