Defects in metal exsolution catalysts: a double-edged role in nanoparticle activity and stability

Metal exsolution - the precipitation of metal nanoparticles from host oxides - holds potential for the design of oxide-supported metal catalysts, relevant for a broad range of applications. In oxides, defects give rise to a wide variety of functional properties that are essential for the performance of oxide-based catalysts. In addition, the nanoparticle exsolution behaviour is closely linked to the defect structure of oxides. Consequently, defect engineering has been established as a strategy to tailor exsolution catalysts, primarily in terms of key morphological nanoparticle properties such as the nanoparticle surface density, typically used as a measure to quantitatively evaluate and compare the exsolution behaviour in oxides. For this purpose, the defect structure of exsolution-active host oxides is often deliberately modified. Moreover, defects may evolve in response to the reducing exsolution reaction conditions, leading to altered functional properties of oxide supports upon exsolution. As a result, defects in exsolution-active oxides mediate nanoparticle properties and support properties under reaction conditions, rendering the control of catalytic performance in exsolution catalysts challenging. In the present perspective paper, I aim to discuss the critical role of defects in metal exsolution synthesis, addressing their impact on nanoparticle and support properties that mediate catalyst activation and degradation processes.