Heteroatom doping effects on interaction of H₂O and CeO₂ (111) surfaces studied using density functional theory: Key roles of ionic radius and dispersion

Understanding heteroatom doping effects on the interaction between H₂O and cerium oxide (ceria, CeO₂) surfaces is crucially important for elucidating heterogeneous catalytic reactions of CeO₂-based oxides. Surfaces of CeO₂ (111) doped with quadrivalent (Ti, Zr), trivalent (Al, Ga, Sc, Y, La), or divalent (Ca, Sr, Ba) cations are investigated using density functional theory (DFT) calculations modified for onsite Coulomb interactions (DFT + U). Trivalent (except for Al) and divalent cation doping induces the formation of intrinsic oxygen vacancy (O_vac), which is backfilled easily by H₂O. Partially OH-terminated surfaces are formed. Furthermore, dissociative adsorption of H₂O is simulated on the OH terminated surfaces (for trivalent or divalent cation doped models) and pure surfaces (for Al and quadrivalent cation doped surfaces). The ionic radius is crucially important. In fact, H₂O dissociates spontaneously on the small cations. Although a slight change is induced by doping as for the H₂O adsorption energy at Ce sites, the H₂O dissociative adsorption at Ce sites is well-assisted by dopants with a smaller ionic radius. In terms of the amount of promoted Ce sites, the arrangement of dopant sites is also fundamentally important.