Surface Reactions of Carbon Dioxide at the Adsorbed Water−Oxide Interface

In this study, FTIR spectroscopy is used to investigate surface reactions of carbon dioxide at the adsorbed water−oxide interface. In particular, FTIR spectra following CO 2 adsorption in the presence and absence of coadsorbed water on hydroxylated nanoparticulate Fe 2 O 3 and γ-Al 2 O 3 at 296 K are reported. In the absence of coadsorbed water, CO 2 reacts with surface O−H groups to form adsorbed bicarbonate on the surface. In the presence of coadsorbed water, this reaction is blocked as water hydrogen bonds to the reactive M−OH sites. Instead, CO 2 reacts with adsorbed water to yield adsorbed carbonate and protonated surface hydroxyl groups, M−OH 2 +, through a proposed carbonic acid intermediate. The carbonate spectra recorded between 10 and 90% RH are nearly identical to that of carbonate adsorbed on these surfaces in the presence of the liquid water. FTIR isotope studies show that there is extensive exchange between oxygen in adsorbed water and oxygen atoms in both adsorbed carbonate and gas-phase carbon dioxide. On the basis of these experimental results along with quantum chemical calculations, a mechanism is proposed for surface reactions of carbon dioxide at the adsorbed water−oxide interface.