Rational Design of Morphological Characteristics to Determine the Optimal Hierarchical Nanostructures in Heterogeneous Catalysis

Abstract

This work draws attention to the optimal hierarchical nanostructure morphology and the morphological characteristics that lead to a rational design of heterogeneous nanocatalysts, especially for reactions that exhibit sluggish kinetics. A simplified methanol oxidation on two types of hierarchical nanostructures, external and internal, is reported. A complex system of asymmetric geometries was simplified by mapping 3 D geometries into 2 D models by using a mass transport approach. The macropore size was the most comprehensive characteristic to evaluate the specific activity and current density of hierarchical nanostructures. The optimal current densities for both types of nanostructures were achieved in macropore size ranges of 3.2–4.5 and 1.9–3.2 μm, respectively. The optimal mass activity of the internal nanostructures was achieved in the porosity range of 40–50 %, whereas that of the external hierarchical nanostructures was achieved at high porosity values. In comparison to internal hierarchical nanostructures, external hierarchical nanostructures tend to be cost‐effective catalysts that have a high catalytic activity.

Confinement of nano-gold in 3D hierarchically structured gadolinium-doped ceria mesocrystal: synergistic effect of chemical composition and structural hierarchy in CO and propane oxidation

“…Also, the pore morphology of the hierarchical support may influence the metal nanoparticle size, shape, 34 and access to the active sites by reagents. 33 Consequently, this may have an impact on the catalytic properties of nanoparticles. Moreover, investigating the influence of the mutual arrangement of the support crystallites in the formation of a hierarchical structure on the catalytic activity may shed light on the structure-activity relationship of these complex systems.…”

“…32 Theoretical modelling has shown that kinetic-controlled oxidation proceeds on the exterior of hierarchical nanostructures, whereas the diffusion-controlled regime occurs in the internal nanostructures. 33 Thus, embedding gold nanoparticles either on the exterior surface of a hierarchical support or inside the material may result in different catalytic behavior depending on the system architecture. Also, the pore morphology of the hierarchical support may influence the metal nanoparticle size, shape, 34 and access to the active sites by reagents.…”