Abstract
In situ X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and scanning tunneling microscopy (STM) were used to study the reduction of potassium-modified Cu2O/Cu(111) by CO. By following the time evolution of the O is peak of Cu2O, we determined that the apparent activation energy for Cu2O reduction by 2 x 10(-4) Torr CO is decreased by similar to 30% in the presence of K. On the K-modified surface, both XPS and IRRAS data show the formation of a surface species identified by IRRAS as carbonate (CO32-), likely forming a K+-CO32- complex, which is stable up to 500 K. STM images show that K+-CO32- complexes form chains around reduced Cu islands, thereby hindering the mass transfer of Cu atoms and preventing the reconstruction of the surface. Theoretical calculations show that the formation of carbonate on the K-modified "44" Cu2O structure is thermodynamically favorable compared to the formation of CO2 on either the bare or K-modified surfaces.