Mechanistic insights into the stepwise oxidation of methane to methanol and formaldehyde over Cu-exchanged SSZ-13.

The partial oxidation of methane to methanol is investigated over Cu-exchanged SSZ-13 using grid-based projector augmented wave within density functional theory and FDMNES XANES simulations. CH4 activation at the Cu-O site proceeds, followed by CH3OH oxidation to HCHO. Projected density of states analysis shows hybridization of the O 2p, Cu 3d, and H 1s orbitals at the transition states, confirming C-H bond activation at the Cu-O moiety. FDMNES simulations reveal a red shift in the Cu K-edge during both steps, indicating Cu reduction and its participation in the redox cycle. These results demonstrate that Cu-O sites are responsible for both methane activation and methanol oxidation with high selectivity toward partial oxidation products.