Interaction of CO2 with Cs-promoted Fe(110) as compared to Fe(110)/K+CO2

The interaction of CO₂ with Cs-promoted Fe(110) at 85 K as well as temperature-dependent reactions between 100 and 700 K have been studied by means of ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Several surface species could be detected at 85 K, i.e. carbon monoxide (CO), carbonate (CO^n?₃), physisorbed linear carbon dioxide (CO^lin₂) and very small amounts of oxidic oxygen (O_ox). An oxalate species (C₂O^m?₄) could not be identified definitively, but from comparison with the literature there is evidence that C₂O^m?₄ is present. Increasing the temperature after saturation with CO₂ leads to a complicated reaction behaviour. CO₂ either desorbs or dissociates into CO and CO^n?₃ or forms C₂O^m?₄ at temperatures between 85 and 160 K. Above 160 K C₂O^m?₄, decomposes in parallel reactions into CO₂, CO^n?₃ and CO. Above 320 K, adsorbed CO either desorbs into the gas phase or dissociates into C and O. In the temperature region between 500 and 700 K a recombination of C and O to CO and the desorption of Cs take place. As in the case of Fe(110)/K+CO₂, at high alkali coverages two carbonate species could be detected which dissociate upon heating at different temperatures. The system Fe(110)/Cs+CO₂ is proved to be very similar to the system Fe(110)/K+CO₂.