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: moaomethylamine (CH3NH2), dimethylamine [(C
H3)(2)NH] and ethylamine (CH3CH2NH2). All three physisorb at the clean surf
ace at 80 K with characteristic N(1s) and C(1s) binding energies in the ran
ge 400.0-400.5 eV and 286.8-286.3 eV, respectively. The amines are more str
ongly 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 b
etween 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 nit
rogen-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 diox
ide interactions are assigned to carbamates [RR'NCO2(a)]. On heating, the c
arbamates desorb leaving no decomposition products at the surface. (C) 2000
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