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Free keywords:
Heteronuclear Oxide Cluster; Infrared Photodissociation Spectroscopy; Ion Trap Mass Spectrometry; Methane Activation; Nickel-Containing Catalyst
Abstract:
The gas-phase reaction of NiAl2O4+ with CH4 is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl2O4H+ and NiAl2O3H2+, are identified in the mass spectra. The DFT calculations predict that the global minimum-energy isomer of NiAl2O4+ 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 (CH3⋅) or formaldehyde (CH2O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O.- site, followed by either CH3⋅ loss or CH3⋅ migration to an O2- site next to the Ni2+ center. The CH3⋅ attaches as CH3+ to O2- 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.
