Facet-Dependent Reactivity of Ceria Nanoparticles Exemplified by CeO2-Based Transition Metal Catalysts: A Critical Review

Abstract

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity of catalyst’s counterparts but also on their interfacial interactions; it can also opening up new horizons for the development of highly active and robust materials. The present critical review, focusing mainly on our recent advances on the topic, aims to highlight the pivotal role of shape engineering in catalysis, exemplified by noble metal-free, CeO2-based transition metal catalysts (TMs/CeO2). The underlying mechanism of facet-dependent reactivity is initially discussed. The main implications of ceria nanoparticles’ shape engineering (rods, cubes, and polyhedra) in catalysis are next discussed, on the ground of some of the most pertinent heterogeneous reactions, such as CO2 hydrogenation, CO oxidation, and N2O decomposition. It is clearly revealed that shape functionalization can remarkably affect the intrinsic features and in turn the reactivity of ceria nanoparticles. More importantly, by combining ceria nanoparticles (CeO2 NPs) of specific architecture with various transition metals (e.g., Cu, Fe, Co, and Ni) remarkably active multifunctional composites can be obtained due mainly to the synergistic metalceria interactions. From the practical point of view, novel catalyst formulations with similar or even superior reactivity to that of noble metals can be obtained by co-adjusting the shape and composition of mixed oxides, such as Cu/ceria nanorods for CO oxidation and Ni/ceria nanorods for CO2 hydrogenation. The conclusions derived could provide the design principles of earth-abundant metal oxide catalysts for various real-life environmental and energy applications.

Shape Effects of Ceria Nanoparticles on the Water‒Gas Shift Performance of CuOx/CeO2 Catalysts

“…The latter is of particular importance, revealing that the high WGS performance is closely related with the relative population of oxygen vacancies and the extent of metal-support interactions. However, various factors, such as support morphology, metal content, and synthesis procedure can exert a profound influence on intrinsic characteristics and metal-support interactions [19,20,32]. In view of this fact, the difference between the present work and the previous ones, in relation to the optimum ceria morphology, could be ascribed to the different loading, preparation procedure and pretreatment protocols.…”

“…In view of this fact, the difference between the present work and the previous ones, in relation to the optimum ceria morphology, could be ascribed to the different loading, preparation procedure and pretreatment protocols. The key role of these parameters towards controlling the metal-support interactions and in turn the catalytic performance has been thoroughly reviewed [19,20,32].…”

“…Despite the extensive work in the field, no definitive conclusions have been drawn in relation to the influence of ceria shape on the redox properties and WGS activity of CuO x /CeO 2 catalysts. The latter is mainly attributed to the fact that besides the support morphology, various other factors, such as metal loading, synthesis procedure and pretreatment protocols can notably affect the intrinsic reactivity and metal-support interactions [19,20,32].…”

“…In view of these aspects and motivated by our previous experience in the field of ceria shape effects in catalysis [27,32], we extended our research efforts to WGS reaction. In particular, three different ceria nanoshapes (polyhedra, cubes and rods) were hydrothermally prepared and used as supports for the copper oxide phase.…”

Rational Design of Non-Precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes

“…Although, noble metals (NMs)-based catalysts are traditionally employed in various processes, due to their peculiar characteristics and enhanced reactivity, their scarcity and consequently high cost renders them disincentive for practical applications. In this perspective, the rational design and development of earth-abundant NMs-free metal oxides of adequate activity, selectivity and durability constitutes one of the main research pillars in heterogeneous catalysis [1][2][3][4][5][6]. Towards this direction, however, one crucial question must be answered: Is it possible to fine-tune the local surface chemistry/structure of a single, binary or multicomponent metal oxide in order to be highly efficient-like NMs-in a specific process?…”