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The Critical Role of Nanoparticle Geometry in Turnover Frequency Calculation
Zohreh Akbari1,2, Loris Lombardo1,2, Andreas Züttel1,2
1Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique Fedérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l'Industrie 17, CH-1951 Sion, Switzerland.
Accurate catalyst evaluation needs nanoparticle geometry. Assuming spherical shapes for catalysts like nickel (Ni) significantly overestimates turnover frequency (TOF), highlighting the need for geometry-specific models in heterogeneous catalysis.
Area of Science:
- Heterogeneous Catalysis
- Materials Science
- Nanotechnology
Background:
- Accurate site-normalized catalytic activity (turnover frequency, TOF) is crucial for comparing catalysts.
- Catalyst nanoparticle (NP) size and geometry significantly influence surface atom fraction and activity.
Purpose of the Study:
- To systematically quantify the impact of NP geometry on surface atom fraction across different crystal structures (FCC, BCC, HCP).
- To evaluate errors in TOF calculations arising from assuming spherical NPs.
- To demonstrate the necessity of geometry-specific models for reliable catalyst performance evaluation.
Main Methods:
- Computational analysis of surface atom fractions for various NP geometries and crystal structures.
- Modeling catalytic H2 combustion (CHC) over an octahedron Ni catalyst on γAl2O3 as a model system.
- Comparison of TOF calculations using geometry-specific vs. spherical NP approximations.
Main Results:
- Assuming spherical NPs underestimates surface atom fraction and leads to an 86% overestimation of TOF in the model experiment.
- Discrepancies are attributed to miscalculations of surface site availability in spherical approximations.
- A framework for geometry-dependent TOF calculations was developed.
Conclusions:
- Geometry-specific models are essential for accurate TOF calculations and reliable comparisons in heterogeneous catalysis.
- Neglecting NP geometry can lead to significant errors in catalyst performance assessment.
- The study provides insights for morphology-controlled catalyst design and facet-specific reactivity optimization.
