FTIR Spectroscopy Combined with Isotope Labeling and Quantum Chemical Calculations to Investigate Adsorbed Bicarbonate Formation Following Reaction of Carbon Dioxide with Surface Hydroxyl Groups on Fe<sub>2</sub>O<sub>3</sub> and Al<sub>2</sub>O<sub>3</sub>

FTIR spectroscopy combined with isotope labeling experiments and quantum chemical calculations is used to investigate the adsorption of carbon dioxide on hydroxylated metal oxide surfaces. In particular, transmission FTIR spectra following CO<sub>2</sub> adsorption on hydroxylated nanoparticulate Fe<sub>2</sub>O<sub>3</sub>, α-Al<sub>2</sub>O<sub>3</sub>, and γ-Al<sub>2</sub>O<sub>3</sub> particles at 296 K are reported. As expected, reaction of CO<sub>2</sub> with these surfaces results in the formation of adsorbed bicarbonate and carbonate. In this study, the vibrational spectrum of the bicarbonate product is analyzed in detail through the use of isotope labeling experiments and quantum chemical calculations. The experimental and calculated vibrational frequencies of adsorbed HC<sup>16</sup>O<sub>3</sub><sup>-</sup>, DC<sup>16</sup>O<sub>3</sub><sup>-</sup>, HC<sup>18</sup>O<sub>3</sub><sup>-</sup>, HC<sup>16</sup>O<sup>18</sup>O<sub>2</sub><sup>-</sup>, and HC<sup>18</sup>O<sup>16</sup>O<sub>2</sub><sup>-</sup> indicate that bicarbonate bonds to the surface in a bridged structure. There is some evidence from the mixed isotope experiments that following initial nucleophilic attack of OH, the formation of the final bicarbonate structure involves a proton transfer. On the basis of energetic considerations, the proton transfer mechanism most likely occurs through an intermolecular process involving either coadsorbed hydroxyl groups and/or carbonate.