Gas‐Phase Mechanism of O(.−)/Ni(2+)‐Mediated Methane Conversion to Formaldehyde

The gas‐phase reaction of NiAl(2)O(4) (+) with CH(4) is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl(2)O(4)H(+) and NiAl(2)O(3)H(2) (+), are identified in the mass spectra. The DFT calculations predict that the global minimum‐energy isomer of NiAl(2)O(4) (+) contains Ni in the +II oxidation state and features a terminal Al−O(.−) oxygen radical site. They show that methane can react along two competing pathways leading to formation of either a methyl radical (CH(3)⋅) or formaldehyde (CH(2)O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O(.−) site, followed by either CH(3)⋅ loss or CH(3)⋅ migration to an O(2−) site next to the Ni(2+) center. The CH(3)⋅ attaches as CH(3) (+) to O(2−) and its unpaired electron is transferred to the Ni‐center reducing it to Ni(+). The proposed mechanism is experimentally confirmed by vibrational spectroscopy of the reactant and two different product ions.