The electronic and chemical reduction properties of the Ce0.75Zr0.25O2(110) surface are presented based on DFT + U calculations, i.e. density functional theory with the inclusion of on-site Coulomb interaction. Experimental studies in the literature have shown that redox activity and thermal stability of ceria are significantly enhanced by the presence of zirconia dopants. In the present theoretical study it is found that mixing zirconia into ceria leads to important structural and chemical consequences such as non-equivalent 0 atoms at the surface, lower reduction energy and larger surface relaxation. The electronic mechanisms behind these modifications are analysed. (C) 2007 Elsevier B.V. All rights reserved.