Methyl
radicals (CH3
•) are the key
intermediates in the heterogeneous–homogeneous reaction processes
of catalytic oxidative coupling of methane (OCM). Here, by applying in situ synchrotron-based vacuum ultraviolet photoionization
mass spectrometry, we quantitatively detected CH3
• being desorbed from various metal oxides and validated the CH3
•-generating capability as an effective
descriptor for the catalytic performance of the metal oxides in OCM.
It is found that the C2 yield is linearly correlated to
the amount and the desorption temperature of CH3
•, with the better OCM catalyst showing stronger CH3
• intensity and lower CH3
• desorption temperature. Furthermore, experimental characterizations
together with density functional theory calculations suggest that
the intrinsic electronic properties of metals and the subsequent generated
electrophilic oxygen species are the decisive factors for CH3
• generation. Then, the CH3
•-generating capability can bridge the gap between the OCM performance
and the structure of the catalyst and help us better understand the
intrinsic structure–performance relationship in OCM over metal
oxide catalysts.
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