Shape Engineering of Oxide Nanoparticles for Heterogeneous Catalysis

Abstract

The fabrication of oxide particles with tunable sizes and shapes at the nanoscale is one of the most crucial issues for the design and development of highly efficient heterogeneous catalysts. The shape of oxide nanoparticles has been demonstrated to affect their catalytic properties remarkably. Tuning the shape of oxide particles allows preferential exposure of specific reactive facets; this can maximize the number of active sites available to the reactants, which can improve the activity and also mediate the reaction route to a specific channel to achieve higher selectivity for a particular chemical reaction. In addition, the shape of the oxide particles affects their interaction with metal particles or clusters, and this involves interfacial strain and charge transfer. Metal particles or clusters dispersed on the reactive or polar facets of the oxide support often provide superior catalytic performance, primarily because of strong metal-support interactions. However, the geometric and electronic features of the metal-oxide interface may change during the course of the reaction, induced by chemisorption of reactive molecules at elevated temperatures, which should be taken into account in proposing a structure-reactivity relationship.

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

“…Nanostructured catalysts possess unique properties originating from nanoscale phenomena linked mainly to size effects, commented above, and shape effects. The latter refers to the modification of catalytic activity through the preferential exposure of specific crystallographic facets on the reaction environment, also termed as morphology-dependent nanocatalysis [51,65,66,70,82,[104][105][106]. In particular, the catalytic cycle and hence the reaction efficiency, is determined on reactants adsorption/activation and products desorption processes, being strongly influenced by the surface planes of catalysts particles.…”

“…In particular, ceria or cerium oxide (CeO 2 ) has attracted considerable attention, due to its unique properties, including enhanced thermal stability, high oxygen storage capacity (OSC) and oxygen mobility, as well as superior reducibility driven by the formation of surface/structural defects (e.g., oxygen vacancies) through the rapid interplay between the two oxidation states of cerium (Ce 3+ /Ce 4+ ) [2,6,38,[46][47][48]. Besides bare ceria's exceptional properties, its combination with transition metals leads to improved catalytic performance, due to the synergy between the metal phase and the support, related to electronic, geometric and bifunctional interactions [40,[49][50][51][52][53][54]. In this regard, the combination of CuO x and CeO 2 oxides towards the formation of CuO x /CeO 2 binary oxides, offers catalytic activities comparable or even better to NMs-based catalysts in various applications, such as CO oxidation, N 2 O decomposition, preferential oxidation of CO (CO-PROX), as lately reviewed [40].…”

“…In view of the above, very recently, the modulation of metal-support interactions as a tool to enhance the catalytic performance was thoroughly reviewed, disclosing that up to fifteen-fold productivity enhancement can be achieved in reactions related to C1 chemistry by controlling metal-support interactions [61]. However, it is well established today-thanks to the rapid development of sophisticated characterization techniques-that various interrelated factors, such as the composition, the size, the shape, and the electronic state of MOs different counterparts can exert a profound influence on the local surface chemistry and metal-support interactions, and in turn, on the catalytic activity of these multifunctional materials [6,48,51,52,[62][63][64][65][66][67][68][69][70][71][72][73][74]. In view of this fact, the fine-tuning of MOs towards the development of catalytic materials with the desired cost, activity, selectivity and stability could be considered the "Holy Grail" in the field of catalyst manufacturing.…”

Decoration of Cube‐Like Ceria Crystals by Well‐Dispersed Au Nanoparticles: Surface Influence

“…If the amount of adsorbed material is too low, no nanoparticles will be visible on the surface of the support and it will be present in the form of a thin layer. [38] In our case, the amount of chloroauric acid (calculated per unit area of the support) was ∼ 10 times larger for the Au/CeO 2 (extra-large cube-like) sample than for Au/CeO 2 (small cube-like) one (Table 1). We believe that, such a difference in coverage by the gold of the ceria surface must have consequences in the final product.…”

“…According to the Stranski‐Krastanov model of crystal growth, the amount of adsorbed material (e. g. metal precursor) is critical to the appearance of particles on the surface of the support. If the amount of adsorbed material is too low, no nanoparticles will be visible on the surface of the support and it will be present in the form of a thin layer . In our case, the amount of chloroauric acid (calculated per unit area of the support) was ∼10 times larger for the Au/CeO 2 (extra‐large cube‐like) sample than for Au/CeO 2 (small cube‐like) one (Table ).…”