Influence of Alloyed Sn on Adsorption and Reaction of NO on Pt(100) Surfaces

Abstract

Adsorption and reaction of NO on the (5 × 20)-Pt(100) surface and two Sn/Pt(100) surface alloys have been studied using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). On the (5 × 20)-Pt(100) surface, in the absence of Sn, NO is primarily reversibly adsorbed, and most of the chemisorbed NO desorbs molecularly from the surface during TPD. Approximately 25% of the adsorbed NO monolayer decomposes at temperatures higher than 400 K, and this leads to N2 and O2 desorption from the surface. Alloying Sn into the surface layer of Pt(100) forms two ordered surface alloys having c(2 × 2) and (3√2 × √2)R45°Sn/Pt(100) surface structures with θSn = 0.5 and 0.67 ML, respectively. Alloying reduced the saturation coverage of NO in the chemisorbed monolayer from that on Pt(100) at 100 K, and it also reduced the adsorption energy of molecularly bound NO by more than a factor of 2. Alloyed Sn, which removes all pure-Pt 2-fold bridge and 4-fold hollow sites, completely ...