Water Formation under Silica Thin Films: Real‐Time Observation of a Chemical Reaction in a Physically Confined Space

Using low‐energy electron microscopy and local photoelectron spectroscopy, water formation from adsorbed O and H(2) on a Ru(0001) surface covered with a vitreous SiO(2) bilayer (BL) was investigated and compared to the same reaction on bare Ru(0001). In both cases the reaction is characterized by moving reaction fronts. The reason for this might be related to the requirement of site release by O adatoms for further H(2)‐dissociative adsorption. Apparent activation energies ([Formula: see text] ) are found for the front motion of 0.59 eV without cover and 0.27 eV under cover. We suggest that the smaller activation energy but higher reaction temperature for the reaction on the SiO(2) BL covered Ru(0001) surface is due to a change of the rate‐determining step. Other possible effects of the cover are discussed. Our results give the first values for [Formula: see text] in confined space.