Gas‐Phase Mechanism of O<sup>.−</sup>/Ni<sup>2+</sup>‐Mediated Methane Conversion to Formaldehyde
Ya‐Ke Li, Fabian Müller, Wieland Schöllkopf, Knut R. Asmis, Joachim Sauer
Abstract
Abstract 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.