Recent Advances on the Design of Group VIII Base-Metal Catalysts with Encapsulated Structures

Inexpensive group VIII metal (i.e., Fe, Co, and Ni)-based solid catalysts have been widely used in various energy transformation processes such as Fischer-Tropsch (F-T) synthesis, reforming, and water gas shift reactions. The emerging encapsulation strategy, which represents active metal species that are coated by a protective shell or matrix, has been demonstrated as a powerful means to promote the catalytic performance (i.e., activity, stability, and selectivity) of Fe-, Co-, and Ni-based catalysts due to synergic effects from the well-defined structures. This review describes recent progress on the design and synthesis of encapsulated group VIII base-metal nanomaterials developed for energy and environmental catalysis including syngas conversion, CO2 dry reforming, steam reforming, methane conversion, and NH3 decomposition. We start with an introduction of the catalysts with different encapsulating structures (e.g., core@shell, yolk@shell, core@tube, mesoporous structures, and lamellar structures). Then, the synthetic methods of Fe-, Co-, and Ni-based catalysts with encapsulated structures are described in detail. The functions of encapsulation structures in catalysis, including protecting metal nanoparticles (NPs) from sintering, promoting the activity due to the confinement effect, and intensifying reaction processes in the form of multifunctional catalysts, are discussed, respectively. Our perspectives regarding the challenges and opportunities for future research in the field are also provided.