A novel method of upgrading natural gas into value-added liquid products is presented, in which the methane is activated by a decoupled oxidation approach with metal-surface facilitation in aqueous system under ambient conditions. A facilitation effect of metal surfaces was discovered to be the critical step for methane activation, and three different liquid products can be produced: methanol, methyl formate, and formic acid. Our results showed that the activation rate of methane on metal surface is strongly correlated with the CH3?M binding energy: The higher binding energy leads to greater activation rate. At the same time, product evolution as well as its final decomposition was also observed along with activation time. In order to understand the evolution of activation products, we studied the decomposition reaction of formic acid in the same aqueous system with tuned conditions. A pseudo-first-order kinetics was observed to well fit the decomposition behavior of formic acid. The results revealed a volcano-shape correlation between the decomposition rates of formic acid with the O?M binding energy. The fundamental understanding of the methane activation and the product decomposition will enable us to further develop this novel methane-upgrading method for industrial scale.