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

Abstract

Methyl radical (CH3•) is the critical precursor to generate C2 hydrocarbons in oxidative coupling of methane (OCM) reaction. It is crucial to explore how to efficiently generate CH3• 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 CH3• 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 CH3• 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 CH3•; 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 CH3•. The study can provide some guidance for designing high efficient OCM catalysts.