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 (So) of ca. 0.1. Experiments with sub-ambient crystal temperatures show much more efficient adsorption with So being 0.9 at 180 K. The adsorption 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.

Isotope Effects in Methanol Synthesis and the Reactivity of Copper Formates on a Cu/SiO2 Catalyst

“…1a, we also observed (spectra not shown) two distinctive yet less intense peaks at 2,933 and 2,848 cm -1 . These have been previously assigned to adsorbed formate species [20,21,30]. The first is a combination band of asymmetric O-C=O stretch and C-H inplane bend modes (m a (CO 2 -)+d(C-H)), while the second arises from the C-H stretch modes.…”

“…These studies have also observed the presence of surface-bound formate species under reaction conditions [16] and also have measured the stability of these species in inert gas and hydrogen [17,18]. Compared with single crystal copper surfaces, the surface species observed on the oxide supported polycrystalline copper system are more complex because of the multi-faceted copper surfaces presented by the supported particles [14,17,[19][20][21] and the presence of species adsorbed on the support materials (e.g., alumina and ceria) as well as the support-metal interface [22]. More complex infrared spectra are observed which makes assignment more difficult than on the single crystals [23][24][25].…”

The role of precursor states in adsorption, surface reactions and catalysis

“…First of all let us consider the reaction between pre-adsorbed oxygen atoms (the base) and gas phase formic acid. The sticking probability of formic acid is low, at *0.1 [20,21], but upon pre-adsorption of oxygen atoms the reaction probability is very high at 0.82 (see Fig. 6) [20,22].…”

“…7); the stoichiometry change with temperature, and the change in product ratios from the formate reaction with oxygen could be fitted by taking into account the formate stability and the importance of precursor state adsorption which has been obtained from surface science investigations from several groups [21][22][23][24][25][26]. The product evolution depends upon temperature in the following way.…”

The reaction of formic acid with Raney TM copper

“…The key intermediate, formate, is readily generated on model single-crystal surfaces by exposure to formic acid vapour and has been extensively studied by both spectroscopic [6,7] and structural methods [8]. These conclude that formate is present in a bidentate coordination mode with the oxygen atoms bonded to adjacent copper atoms along the rows (figure 1).…”