The use of CH4 and CO2 to produce value‐added chemicals via direct C−C coupling is a challenging chemistry problem because of the inertness of these two molecules. Herein, mass spectrometric experiments and high‐level quantum‐chemical calculations have identified the first diatomic species (CuB+) that can couple CH4 with CO2 under thermal collision conditions to produce ketene (H2C=C=O), an important intermediate in synthetic chemistry. The order to feed the reactants (CH4 and CO2) is important and CH4 should be firstly fed to produce the C2 product. Molecular‐level mechanisms including control of product selectivity have been revealed for coupling of CH4 with CO2 under mild conditions.