Co-adsorption of Formic Acid and Potassium on Cu{100}: A Temperature Programmed Desorption Study

The adsorption and decomposition of formic acid (hcooh) co-adsorbed with k on cu{100} has been studied by the spectroscopic technique of temperature programmed desorption (tpd). for the adsorption of k on cu{100}, the activation energy for desorption falls drastically with increasing coverage from 214 kj.mol-1 at the low coverage of 0.01 ml (ml=monolayer) to 139 kj.mole-1 at close to completion of the first potassium layer (0.35 ml). the pre-adsorption of cu{100} by a saturation coverage ( > 10 ml) of hcooh instigates a different adsorption-desorption behaviour compared to the k/cu{100}. below and at the low k coverage of 0.009 ml on hcooh pre-adsorbed on cu{100}, a destabilization of the predominantly strong polar covalent cu-k bonding occurs indicated by the significant decrease in the desorption peak temperature (tp) from 800k to 560k. at a coverage of 0.02 ml, the peak temperature is found to split to lower values pertaining the original high tp. this behaviour can be explained by the formation of k-hcooh compounds that desorb at different tp values. at higher k coverages on pure cu{100}, a weaker cu-k bonding takes place and a metallic-like potassium behaviour emerges which is attributed to the presence of lateral k-k interactions. at higher k coverages (>0.025 ml) on the cu{100} pre-adsorbed with hcooh, a very complex tpd spectrum is obtained. a complex range of k-hcooh reaction products might be the only way to explain such a spectrum.