The reaction of carbon dioxide with amines at a Cu(211) surface

The activation of carbon dioxide by different amines has been studied at 80 K at clean Cu(211) surfaces using X-ray photoelectron spectroscopy (XPS). Three amines were investigated: monomethylamine (CH3NH2), dimethylamine [(CH3)2NH] and ethylamine (CH3CH2NH2). All three physisorb at the clean surface at 80 K with characteristic N(1s) and C(1s) binding energies in the range 400.0–400.5 eV and 286.8–286.3 eV, respectively. The amines are more strongly bound to the surface than ammonia, desorbing molecularly between 250 and 290 K, whereas ammonia desorbs from copper surfaces at about 170–190 K. The extra stability of the amines is attributed to a greater interaction between the surface and the nitrogen lone pair. Carbon dioxide physisorbs at clean Cu(211) surfaces and desorbs by 130 K, but when coadsorbed with the amines, XPS spectra show high concentrations of an oxygen-, carbon- and nitrogen-containing species to temperatures above 450 K. On the basis of the N:O:C stoichiometries, the thermal stability of the species and the binding energies of the associated XPS peaks, the products of the amine–carbon dioxide interactions are assigned to carbamates [RR′NCO2(a)]. On heating, the carbamates desorb leaving no decomposition products at the surface.