Boosting the generation of key intermediate methyl radical (CH3•) in OCM reaction on magnesium oxide catalysts by regulating the electronic state of the active site.

• The process of methane dissociation to produce methyl radical (CH 3 •) is studied in this work. • The electron-deficient state can be formed by Li doped, however it will be broken once the oxygen vacancy appears. • The active site with electronic-deficient state is the key to the efficient generation of CH 3 •. • A volcano relationship between the C-H activation energy and the H adsorption free energy exists on the Li doped MgO surfaces. Methyl radical (CH 3 •) is the critical precursor to generate C 2 hydrocarbons in oxidative coupling of methane (OCM) reaction. It is crucial to explore how to efficiently generate CH 3 • and reveal the intrinsic principles behind it. In this study, we select MgO with a relatively simple structure as the research object, and probe the effects of the electronic state of active site on the CH 3 • generation by the density functional theory (DFT) calculation. The results show that the pure MgO with the different crystal surfaces as the benchmark models exhibit poor catalytic performance for CH 3 • generation; while Li doped MgO surface or subsurface that have the electron-deficient of active sites, exhibit excellent catalytic performance for it, which is attributed to that the electron-deficient of active sites are easier to receive electron of H and thereby promote the efficient generation of CH 3 •; pure MgO surface or subsurface with oxygen vacancy as well as Li doped MgO surface or subsurface with oxygen vacancy as the contrast models that have the electron-rich of active sites, exhibit poor catalytic performance. It can be obtained that the active site with electronic-deficient state is the key to the efficient generation of CH 3 •. The study can provide some guidance for designing high efficient OCM catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]