Due to its excellent redox properties, ceria is extensively used in heterogeneous catalysis, where it can act as an oxygen buffer in oxidation reactions or prevent coking of metal phases in hydrocarbon reforming reactions. In this work, ceria-supported platinum-group metal (Pt, Pd, Ir, Rh, Ru) nanoparticles were prepared in a single step by solution combustion synthesis, a simple and inexpensive method favoring metal-oxide interaction and thermal stability [1-3]. The powders were characterized by a variety of techniques (HRTEM, SEM, XRD, XPS, Raman spectroscopy, etc.) and systematically compared for CO oxidation and preferential CO oxidation in excess of hydrogen (PROX) in a flow-fixed-bed reactor. Ceria-supported Rh and Pt appear as the most efficient catalysts in CO oxidation (CO:O2 = 2:2 mol% of 1 atm) and PROX (CO:O2:H2 = 2:2:48 mol%), respectively [3]. These two systems, as well as pristine ceria, were further selected for a comparative operando DRIFTS-MS study, with particular focus on the effect of CO+O2 conditions on the nature of the adsorbed species. Whereas the reaction starts above 150 °C on CeO2 and Rh–CeO2, and does not depend on the state of the surface (i.e. pre-exposed to CO:O2 4:4 mol% or 7:1 mol% mixture), Pt–CeO2 shows strong dependency on the initial state and substantial activity is achieved at much lower temperatures with the CO-rich feed. On the basis of IR data, this result was related to a change in Pt oxidation state via strong interaction with ceria [4]. [1]T.S. Nguyen et al., J. Mater. Chem. A 2, 19822 (2014). [2]G. Postole et al., Appl. Catal. B 166-167, 580 (2015). [3]T.S. Nguyen et al., Catal. Today 253, 106 (2015). [4]A. Kaftan et al., Catal. Sci. Technol., in press (DOI: 10.1039/c5cy00827a)