A Theoretical Study of Surface Reduction Mechanisms of CeO 2 ACHTUNGTRENNUNG ( 111 ) and ( 110 ) by H 2

Ceria (CeO2) is an important catalyst in various industrial and environmental applications such as a three-way automotive exhaust catalyst (TWC), oxygen storage, the oxidation of hydrocarbons and CO, and the decomposition of alcohols and aldehydes. Moreover, rare-earth-doped CeO2, such as gadolia-doped ceria (GDC), has also been used as an electrolyte for low-temperature solid oxide fuel cells (SOFCs). To understand the catalytic properties of both pure CeO2 and metal/ CeO2 materials, it is imperative to examine the redox surface chemistry. Although many studies regarding the defect chemistry of CeO2 have been conducted, [8] its reduction processes have been scarcely examined. In particular, the defect chemistry of CeO2 under H2 atmosphere has been studied by various experimental techniques, such as temperature-programmed reduction (TPR) and NMR. On the basis of experimental results obtained by using TPR and temperature programmed desorption mass spectrometry (TPD-MS), Bernal and coworkers reported that H2–CeO2 interactions are a surface process rather than the hydroxylation and incorporation of hydrogen into the bulk, as proposed by Bruce and coworkers. Although numerous theoretical investigations on bulk CeO2, its surfaces (including reduced ceria), [14–20] and the interactions of atomic H with CeO2ACHTUNGTRENNUNG(111) and (110) [18] have been reported, to the best of our knowledge, the mechanisms of H2– CeO2 interactions have not been adequately addressed. In this study, we report the reduction mechanisms of CeO2ACHTUNGTRENNUNG(111) and (110) surfaces by H2 using periodic density functional theory (DFT) methods. In particular, to properly characterize the electronic structure of CeO2, the DFT+U method [15,20–23] was applied. Detailed potential-energy surfaces for all low-lying reaction pathways are reported.