Spectroscopic and kinetic studies of formic acid adsorption on Cu(110)

Abstract

The adsorption of formic acid on Cu(110) has been studied using Fourier-transform reflection/absorption IR spectroscopy (FTRAIRS) and molecular beam measurements. The adsorption is inefficient at 300 K, having an initial sticking coefficient (S₀) of ca. 0.1. Experiments with sub-ambient crystal temperatures show much more efficient adsorption with S₀ being 0.9 at 180 K. The absorption appears to be of the precursor type. FTRAIRS indicates that the species adsorbed at 200 K is very different from that at 300 K. The latter is the usually reported bidentate formate with a simple IR spectrum and symmetrically equivalent oxygens. At 200 K we propose that formate is produced in the monodentate form, that is strongly anchored to the surface through one oxygen, with the other in the form of a carbonyl group. However, the carbonyl group may also be bonding to the surface weakly. The monodentate species converts to bidentate upon heating. If the bidentate formate is cooled to 200 K, formic acid can be adsorbed from the gas phase and this converts all the formate on the surface back to the monodentate form.