Mass transport and catalytic activity in hierarchical/non-hierarchical and internal/external nanostructures: A novel comparison using 3D simulation

Abstract

The distinct organization of nanostructured materials influences several catalytic characteristics, like selectivity, sensitivity or catalytic efficiency. This paper studies the effect of geometrical configuration of nanostructured catalyst on mass transport and catalytic activity based on 3D simulations of hierarchical external, hierarchical internal, non-hierarchical external and non-hierarchical internal nanostructures. Generally, external nanostructures revealed higher utilization of catalytic surface than the internal nanostructures. Among the four investigated nanostructures, the mass transport in hierarchical external nanostructures was found to be the best; they even showed kinetic controlled regime for the species with low diffusion coefficient. In contrast, hierarchical internal nanostructures showed slightly less specific activity than non-hierarchical internal nanostructures because of higher total diffusional resistance and longer diffusional path. As a result, although hierarchical nanostructures possess large surface area, only the hierarchical external nanostructures provided an outstanding accessibility of active sites. The obtained results provide the tool for understanding the catalytic efficiency in complex nanostructure and phenomena that are technically difficult to measure.