Interaction of carbon dioxide with clean and oxidised Nd/Cu(100)

Abstract

The interaction of carbon dioxide with metallic Nd overlayers and pre-oxidised Nd films on Cu(100) has been investigated by XPS, UPS, Δϕ measurements and temperature-programmed desorption (TPD). Corresponding observations have also been made with H₂O in place of CO₂. Exposure of Nd overlayers to CO₂ at 300 K leads initially to complete dissociation of the molecule with formation of an oxygen-deficient neodymium oxide. Further gas exposure leads to the formation of a CO^(–)_x(x= 2 or 3) species, which on raising the temperature decomposes, yielding first CO and then CO₂ in the gas phase. The interaction of CO₂ with pre-oxidised Nd films proceeds in a manner which is essentially independent of the nature of the pre-oxidising agent (O₂ or CO₂ itself). Quantitative evaluation of the XP spectra indicates that oxide to carbonate conversion occurs leading to the formation of one or more types of carbonate species. The relevance of the work to the poisoning characteristics of Cu/lanthanide alloy-derived methanol synthesis catalysts is noted.