Non-activated adsorption of methane on nickel surfaces induced by reduced work function

Adsorption of methane has been studied in ultrahigh vacuum environments on single crystalline Ni (100) as well as on Ni nano-particles on mica substrates. Experimental techniques have been X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and temperature programmed desorption spectroscopy (TPD). In accordance with previous observations only physisorption of CH4 is observed on pure nickel at temperatures below 130 K for exposures in the high vacuum regime. TPD in the temperature range from 200 to 300 K shows that chemisorption of methane takes place when the sample work function is lowered by about 0.7 eV by a surface treatment, which presumably exposes the surface to atomic hydrogen. The lowered work function enables charge transfer from the Ni conduction band to the methane affinity level which subsequent leads to dissociative chemisorption.