Ceria-zirconia mixed oxides are key materials both as catalysts and as catalyst supports of noble metal nanoparticles, for a variety of chemical processes related to Environmental Catalysis. It is widely accepted that one of the key properties of ceria-zirconia oxides in their role as catalysts or catalyst supports is their ability to exchange lattice oxygen with reactants, usually referred to as Oxygen Storage Capacity (OSC). Such capacity is coupled to the Ce4+/Ce3+ redox exchange, i.e. to the reducibility of the oxide, which is dependent on a number of textural, structural and compositional factors. These factors are not independent but, instead, they are intimately related to each other and connected through thermochemical treatments. Disentangling the complex relationships existing between them has been the focus of a very intense research which has finally led to a model which rationalizes the relationships existing between redox performance, nanostructure and pretreatment conditions.
However, access to Rare Earth Elements (REE) and Platinum Group Metals (PGMs) is nowadays considered a major limiting factor for the development of Green Technologies, a quite relevant aspect from both economic and geo-strategic points of view. Thus, low lanthanide contents and a noble-metal free formulation have become a topic in which an impact of current research is expected.
Taking into account the basic scientific knowledge, particularly that related to the key role of the surface structure of these oxides, our strategy relies on synthesizing new materials which incorporate ceria (CeO2) as nanometer thick surface layers coherently grown onto the surface of a carrier oxide (ZrO2, YSZ). The analysis of the Redox properties of this new type of catalysts, which play in fact a key role in their catalytic performance in a variety of reactions, indicates a large improvement with respect to materials based on bulk ceria. A better performance is observed both in H2-reducibility at low temperatures as well as in the stability of the redox response against aging treatments at very high temperatures.
Electron microscopy analysis of these new materials has been key both to check the success in the nanostructuration targets proposed for their synthesis and indeed, more important, to understand the behavior observed at macroscopic level in their redox properties. Summarizing, these materials not only mimic but also surpass the redox performance of noble metal loaded catalysts based on bulk ceria-zirconia mixed oxides emphasize a more efficient usage of ceria in terms of redox exchange capacity.