Adsorption and dissociation of CO on Rh(210)

Abstract

Adsorption, desorption and decomposition of carbon monoxide on a Rh(210) surface have been investigated in the temperature range between 300 and 1100 K by combined temperature programmed static secondary ion mass spectrometry (TPSSIMS), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Following adsorption of CO at 300 K three different molecular binding states, α1, α2 and α3, are formed and identified through TPD. Partial decomposition of COad takes place during heating. Cad and Oad build-up have been followed by monitoring the relative ΣnRhnX+Rhn+ (n = 1, 2; X = O, C)cluster ion intensities in (TP)SSIMS. At higher temperatures, i.e., above 500 K, Cad and Oad recombine as evidenced by the occurrence of a β-CO feature in TPD. This process is associated with a decrease of the ΣnRhnX+Rhn+ ratios. Further support for partial CO decomposition on Rh(210) is obtained from XPS. Carbon and oxygen show up in C 1s and O 1s features at 283.7 and 530.1 eV, respectively. Their intensities are about 10% of those found for a saturated CO layer at 300 K. Only the α3 state seems to be implicated in the decomposition process as low exposures to CO, for which only the α3 state is occupied, lead to the same amount of carbon and oxygen as high exposures.