The thermal reaction of methane with the metal-free cluster cation [Si<sub>2sub>O<sub>4sub>]<sup>.+sup> has been examined by using Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. In addition to generating a methyl radical via hydrogen-atom abstraction, [Si<sub>2sub>O<sub>4sub>]<sup>.+sup> can selectively oxidize methane to formaldehyde. The mechanisms of these rather efficient reactions have been elucidated by high-level quantum-chemical calculations.