The Critical Role of Nanoparticle Geometry in Turnover Frequency Calculation

Accurate evaluation and comparison of site-normalized catalytic activity (turnover frequency, TOF) in heterogeneous catalysis require consideration of catalyst nanoparticle (NP) size and geometry. In this study, we systematically quantify the impact of NP geometry on the fraction of surface atoms across FCC, BCC, and HCP crystal structures with various geometries and evaluate the absolute and relative errors introduced by assuming spherical NPs. Using catalytic H₂ combustion (CHC) over an octahedron Ni catalyst supported on γAl₂O₃ as a model experiment, we demonstrate that assuming spherical single-crystal Ni NPs underestimates the fraction of the surface atoms and overestimates TOF by 86%. This discrepancy arises from the miscalculation of surface site availability in spherical approximations. These findings emphasize the need for geometry-specific models to ensure reliable TOF calculations and accurate catalyst performance comparisons in heterogeneous catalysis. We work provide a framework for geometry-dependent TOF calculations, offering new insights into morphology-controlled catalyst design and facet-specific reactivity optimization.