Abstract
Adsorption and decomposition of acetic acid were studied by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, and temperature-programmed desorption on Pt/CeO2(111) model catalysts prepared on Cu(111). Reference experiments under identical conditions were performed on stoichiometric CeO2(111), partially reduced CeO2-x, and oxygen pre-exposed O/Pt/CeO2(111)/Cu(111).
The principal species formed on all samples during adsorption of acetic acid at 150 K were acetate and molecularly adsorbed acetic acid. On the basis of the differences in the splitting between the methyl and carboxyl/carboxylate groups in the C 1s spectra, we identified the adsorption sites for acetate and molecularly adsorbed acetic acid on Pt/CeO2.
During annealing, we detected an increase in the concentration of acetate on CeO2(111) support exclusively in the presence of supported Pt particles. The effect is caused by the decomposition of molecularly adsorbed acetic acid on Pt particles followed by spillover of acetate to CeO2(111) support.
The following surface crowding by acetate on CeO2(111) support alters the decomposition mechanism of acetate with respect to the Pt-free CeO2(111). In particular, the formation of ketene and acetone was largely eliminated on Pt/CeO2.
We assume that the surface crowding by acetate triggers a switch in the adsorption geometry of acetate from the bidentate to the monodentate configuration. The acetates in both adsorption geometries were identified according to the different splitting between the methyl and carboxylate groups in the C 1s spectra.
Decomposition of acetate did not leave behind any surface carbon on Pt-free CeO2. In contrast, carbonaceous residues were found on CeO2-x, and Pt/CeO2.
The carbon residues were oxidatively removed above 500 K only from Pt/CeO2.