CO Oxidation on a Single Pd Atom Supported on Magnesia

The oxidation of CO on single Pd atoms anchored to MgO(100) surface oxygen vacancies is studied with temperature-programmed-reaction mass spectrometry and infrared spectroscopy. In one-heating-cycle experiments, ${\mathrm{CO}}_2$, formed from ${\mathrm{O}}_2$ and CO preadsorbed at 90 K, is detected at 260 and 500 K. Ab-initio simulations suggest two reaction routes, with $\mathrm{Pd}(\mathrm{CO}{)}_2{\mathrm{O}}_2$ and $\mathrm{Pd}{\mathrm{CO}}_3\mathrm{CO}$ found as precursors for the low and high temperature channels, respectively. Both reactions result in annealing of the vacancy and induce migration and coalescence of the remaining Pd-CO to form larger clusters.