LEED and thermal desorption studies of small molecules (H 2, O 2, CO, CO 2, NO, C 2H 4, C 2H 2 and C) chemisorbed on the stepped rhodium (755) and (331) surfaces

Abstract

The chemisorption of H 2, O 2, CO, CO 2, NO, C 2H 2, C 2H 4 and C has been studied on the clean stepped Rh(755) and (331) surfaces. Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) were used to determine the size and orientation of the unit cells, desorption temperatures and decomposition characteristics for each adsorbate. All of the molecules studied readily chemisorbed on both stepped surfaces and several ordered surface structures were observed. The LEED patterns seen on the (755) surface were due to the formation of surface structures on the (111) terraces, while on the (331) surface the step periodicity played an important role in the determination of the unit cells of the observed structures. When heated in O 2 or C 2H 4 the (331) surface was more stable than the (755) surface which readily formed (111) and (100) facets. In the CO and CO 2 TDS spectra a peak due to dissociated CO was observed on both surfaces. NO adsorption was dissociative at low exposures and associative at high exposures. C 2H 4 and C 2H 2 had similar adsorption and desorption properties and it is likely that the same adsorbed species was formed by both molecules.