The Synergy of Dilute Pd and Surface Oxygen Species for Methane Upgrading on Au3Pd(111)

The grandest challenge in the direct upgrade of methane to useful chemicals is finding a catalyst that is active for the difficult C-H bond scission yet selective such that not all of the C-H bonds break to form coke or CO2. The Au3Pd(111) surface is studied for methane activation, particularly due to its surface geometry containing a single Pd atom fully surrounded by Au atoms. Through density functional theory (DFT) calculations, the nonoxidative and oxidative mechanisms for methane activation are examined. In the nonoxidative mechanism, the initial C-H bond scission on Au3Pd(111) resembles that of Pd(111), but the subsequent dehydrogenation steps are more difficult than the first, mimicking pure Au(111). In the oxidative mechanism, the dilute Pd atom in Au3Pd(111) draws oxygenated adsorbates to the weakly binding Au surface to assist in the activation of methane. In both cases, Au3Pd(111) merges the activity of pure Pd(111) and the selectivity of pure Au(111), indicating the promise of isolated reactive metals as a potential catalyst for the upgrade of methane and other dehydrogenation processes.