Description of H ₂ Chemisorption on Platinum Particles Using A Geometric Approach

The chemisorption of hydrogen on the surface of metal particles is the most common chemical technique used for estimating dispersion (D(%)) and particle size (d), especially for platinum. However, the stoichiometry of the adsorbate per surface metal atom (H/PtS) remains controversial, which leads to an inaccurate estimation of D and d. The major challenge is therefore to develop a reliable mathematical model that integrates both geometry (in our case, truncated octahedron-type clusters) and adsorption stoichiometry. For the latter, we will base our work on the most favorable adsorption sites using results from DFT calculations found in the literature. The goal is to obtain an accurate estimate of particle dispersion and size. The developed model accurately describes how stoichiometric values vary with particle size, a relationship that is physically tied to the evolution of surface adsorption sites. By quantifying the number of surface atoms and specific surface sites, our model can predict the H/PtS value for any given particle size. Validated against both our laboratory’s experimental data and published literature, this study proposes a methodology based on the geometric model and thus enables a better understanding of the structure–activity relationships of supported metal catalysts.