Interactions between S 18O 2 and NO on the surface of stepped Pt(3 3 2)

Abstract

Interactions between S 18O 2 and NO on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Adsorbed S 18O 2 does not seem to have a preference for step sites on Pt(3 3 2). As such, the presence of S 18O 2 molecules following exposures of ⩽1.6 L does not significantly block the subsequent adsorption of NO (⩽0.8 L) on these step sites. Adsorbed S 18O 2 molecules undergo dissociation (S 18O 2(a) → S 18O(a) + 18O(a)) as the surface temperature is increased to 250 K and above, but the resultant 18O(a) further reacts with sulfur oxides (S 18O 2(a) and S 18O(a)) to form S 18O x ( x > 2) species at ∼400 K and above. The S 18O x species desorb as S 18O 2. Even though the presence of co-adsorbed S 18O 2 suppresses NO dissociation and subsequent N 2 production, this effect is not significantly enhanced with increasing the exposures of S 18O 2 in the range ⩽1.6 L; N 2 desorption is still detectable at an exposure of 1.6 L S 18O 2, at which a considerable amount of S 18O 2 desorption is detected.