Adsorption and activation of CO2 on Pt/CeOx/TiO2(110): Role of the Pt-CeOx interface

Abstract

The adsorption and dissociation of CO2 on TiO2(110), CeOx/TiO2(110) and Pt/CeOx/TiO2(110) surfaces has been examined using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS). The substrates under study exhibited different degrees of complexity which were tested for the binding of the adsorbate and the cleavage of C-O bonds. The surfaces were prepared by depositing CeOx (0.1 ML) onto TiO2(110) to form a mixed oxide support, onto which Pt nanoparticles (0.2 ML) were deposited. This configuration yields a complex set of interfaces between metal and oxides and we have systematically titrated the active role of each component (Pt 4f, Ce 3d and Ti 2p regions) and the arising surface intermediates (C 1 s and O 1 s regions). CO2 barely bonds to stoichiometric TiO2(110). It heals oxygen vacancies of this oxide surface (CO2,gas → COgas + Oa) and does not form stable carbonates. A stable carbonate was seen upon adsorption of CO2 on CeOx/TiO2(110) and on this type of substrate the adsorbate also removed O vacancies leading to the oxidation of Ti3+and Ce3+ sites. Pt nanoparticles dispersed on CeOx/TiO2(110) were highly effective for the binding and dissociation of CO2, with the formation of CO3, CO, C and CHx species on the Pt/CeOx/TiO2(110) system. The results of theoretical calculations based on density-functional theory (DFT) show that Pt/CeOx/TiO2(110) binds CO2 much stronger than surfaces of bulk platinum {(111), (100), (110)} or other late transition metals. On a Pt-CeOx interface, the molecule adsorbs with a bent configuration (~130° O-C-O bond angle) and with a substantial elongation (~ 0.1 Å) of the C-O bonds, facilitating its transformation into high value chemicals.