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

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. Measuring morphology: Heterogeneous catalysis on hierarchical nanostructures exhibits a significant dependence on the morphological aspects, such as roughness, porosity, and macrostructure size. Compared to internal hierarchical nanostructures, external hierarchical nanostructures exhibit optimal morphological characteristics that lead to a higher catalytic activity (specific activity, current density, and mass activity), especially in systems that have sluggish kinetics.