Direct and selective coupling of methane into high-value added products under mild conditions is a grand challenge since the activation of the inert C-H bonds (439 kJ mol− 1) and the inhibition of over-oxidation are simultaneously required. Herein, we report the fabrication of a noble-metal free Ni2+-doped MgO/Al2O3 photocatalyst (NiMgAl-x, x represents calcination temperature) through facile topotactic conversion of the corresponding NiMgAl-layered double hydroxides (denoted as NiMgAl-LDH). EXAFS spectroscopy demonstrates that for NiMgAl-x, the Ni2+ ions are isomorphically doped into MgO cell and no NiO phase is formed. By involving trace amounts of water, photo-oxidation of methane to ethane can be accomplished by using NiMgAl-800 as catalyst in a flow reactor with a high production rate (454.30 µmol g− 1 h− 1) and a superior selectivity (97.8%), which was the highest yield among all the noble-metal free photocatalysts reported so far. Detailed characterizations reveal the electron-enriched surface oxygens of NiMgAl-800 generated during the topotatic process lead to the enhanced photocatalytic activity. In-situ DRIFT experiments and DFT calculations show that the introduced H2O molecules can modulate the Gibbs free energy of ŸCH3 towards a coupling conductive pathway instead of production of CO2, resulting in an increased C2H6 selectivity and inhibited CO2 production.