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Thermochemical energy storage (TCS) based on reduction-oxidation cycles of multivalent metal oxides is of great interest for concentrating solar facilities, as it can allow enhancing the global plant efficiency and improving the energy generation dispatchability. However, to guarantee the feasibility of the process, selected materials should present long term durability, which requires the evaluation of the redox couple cyclability. In this work we have demonstrated, for the first time, the suitability of the Mn 2 O 3 /Mn 3 O 4 pair for this application during 30 cycles, performed in thermobalance. Nevertheless, an appropriate design of such materials is crucial since it has been found that initial particle size influences the redox behaviour of these oxides. Results showed a 2-fold influence of particle size of the as-prepared materials on the redox reversibility. Firstly, this parameter affects to the thermodynamics and kinetics of the redox reactions. Namely a decrease of the particle size shifted the oxidation temperature to lower values and produced slower reduction and oxidation reactions. Secondly, depending on the particles size, samples followed different sintering mechanisms. This fact influenced dramatically the behaviour of the materials with lower particle size, which suffered from a higher degree of densification that eventually caused a total loss of cyclability. † Electronic supplementary information (ESI) available: XRD patterns; high resolution TEM micrographs; SEM micrographs, rst cooling step interval; DSC curves for M 1 sample. See

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Catalytic activity tests in combination with characterization studies (using CO temperature programmed reduction, electron paramagnetic resonance, and Fourier transform infrared) have been performed with the aim of establishing which are the main factors influencing the reactivity of an oxidized Pt/CeO 2 /Al 2 O 3 catalyst for the CO-O 2 reaction. Several effects are induced by the presence of both platinum and dispersed ceria in the catalyst. The results show that the low-temperature reducibility of both platinum and dispersed ceria is enhanced when the two components are present in the catalyst. Analysis of the characteristics of the centers responsible of the latter effect, carried out by means of EPR using oxygen as the probe molecule, indicates that in this sample the most reducible sites are formed by platinum located on bidimensional ceria patches present at the alumina surface. The enhancement by ceria of the low-temperature reduction of platinum at these sites under a CO + O 2 reacting mixture, observed even when starting from oxidized catalysts, leads us to propose these sites as highly active for the CO oxidation reaction.