Time-resolved UV/vis-DR (diffuse reflectance UV/vis) spectroscopy was used to in situ monitor the dynamics of reduction and reoxidation of Pt-free and Pt-containing CeO(2)-ZrO(2) used as oxygen storage capacitors. This method can be also applied for measuring the speed of oxygen release. Combining the spectroscopic catalyst characterization with transient reaction analysis (alternating feeding of CO(H(2)) and O(2)) enabled us to identify factors determining surface and bulk redox processes of ceria. The presence of Pt increased strongly the mobility and availability of lattice oxygen in CeO(2)-ZrO(2) for oxygen release reactions, while the presence of strongly polymerized CeO(x) species (non-homogeneous distribution of ZrO(2) in CeO(2)) decreased the mobility of lattice oxygen. The results of the present in situ UV/vis-DR analysis support previous non-directly derived conclusions. (C) 2010 Elsevier B.V. All rights reserved.