| Summary: | The activation reactions of methane mediated by metal carbide ions <i>M</i>C<sub>3</sub><sup>+</sup> (<i>M</i> = Ir and Pt) were comparatively studied at room temperature using the techniques of mass spectrometry in conjunction with theoretical calculations. <i>M</i>C<sub>3</sub><sup>+</sup> (<i>M</i> = Ir and Pt) ions reacted with CH<sub>4</sub> at room temperature forming <i>M</i>C<sub>2</sub>H<sub>2</sub><sup>+</sup>/C<sub>2</sub>H<sub>2</sub> and <i>M</i>C<sub>4</sub>H<sub>2</sub><sup>+</sup>/H<sub>2</sub> as the major products for both systems. Besides that, PtC<sub>3</sub><sup>+</sup> could abstract a hydrogen atom from CH<sub>4</sub> to generate PtC<sub>3</sub>H<sup>+</sup>/CH<sub>3</sub>, while IrC<sub>3</sub><sup>+</sup> could not. Quantum chemical calculations showed that the <i>M</i>C<sub>3</sub><sup>+</sup> (<i>M</i> = Ir and Pt) ions have a linear M-C-C-C structure. The first C–H activation took place on the Ir atom for IrC<sub>3</sub><sup>+</sup>. The terminal carbon atom was the reactive site for the first C–H bond activation of PtC<sub>3</sub><sup>+</sup>, which was beneficial to generate PtC<sub>3</sub>H<sup>+</sup>/CH<sub>3</sub>. The orbitals of the different metal influence the selection of the reactive sites for methane activation, which results in the different reaction channels. This study investigates the molecular-level mechanisms of the reactive sites of methane activation.
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