A THEORETICAL AND EXPERIMENTAL-STUDY OF REACTION PATHWAYS FOR THE INTERACTION OF CO2 WITH ALKALI-MODIFIED SURFACES

Previous work has shown that CO2 adsorption on bulk potassium leads to the formation of oxalate ions below room temperature. These C2O4 grou ps decompose in vacuo to carbonates, CO3, and CO around 300 K and the carbonates further to oxides and carbon dioxide above 700 K. The prese nt work addresses reaction routes by calculations of adsorption coordi nates in combination with spectroscopic data from time-resolved in sit u infrared spectroscopy and analyses of desorbing species. Oxalate int ermediates are formed by reactions between surface CO2- ions and adsor bed neutral molecules. Weakly adsorbed CO2 alone cannot follow this ro ute. The energetics of oxalate formation is compared with CO2 adsorpti on on clean and oxidized potassium. Rearrangements between almost isoe nergetic oxalates are discussed in connection with reaction routes and branching ratios. CO is released from one oxalate isomer, C2O42--->CO 32-+CO, with only a small activation barrier and bound as an entity in a K:CO complex at multilayer coverages. Desorption is only observed a fter annealing to around 650 K. Finally, CO and CO2 release as a resul t of carbonate decomposition and the reverse formation of CO3 are disc ussed, although these reactions are substrate dependent and nor merely a rearrangement of an alkali compound.