Stabilization of Methanol at Near-Ambient Conditions on a Noble Metal Surface

Pure methanol desorbs from pristine Ag(111) surfaces under ultrahigh vacuum conditions at 160 K, limiting its availability in catalysis on this surface. To combat this, we devise how to adsorb methanol at room temperature without additives. The methanol adsorption near ambient pressures yields monosized trimers. We use low-temperature scanning tunneling microscopy and single-molecule manipulation to investigate the binding pattern of these clusters and compare them to hexamers formed at low pressure below the methanol desorption temperature. Supported by density functional theory, we unravel that the low-temperature, low-pressure clusters are hydrogen bonded cyclic hexamers, while the room temperature, high-pressure clusters are stabilized by stronger hydrogen bonds of three methanol molecules to a central chemisorbed oxygen atom. Our study shows that trace amounts of oxygen adatoms formed from methanol at high pressure on the Ag(111) surface may aid heterogeneous methanol chemistry under ambient conditions by increasing the residence time on a catalyst surface.