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Materials (Basel). 2018 May 16;11(5). pii: E819. doi: 10.3390/ma11050819.

Palladium, Iridium, and Rhodium Supported Catalysts: Predictive H₂ Chemisorption by Statistical Cuboctahedron Clusters Model.

Author information

1
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. Fabien.drault@univ-poitiers.fr.
2
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. clement.comminges@univ-poitiers.fr.
3
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. fabien.can@univ-poitiers.fr.
4
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. laurence.pirault@univ-poitiers.fr.
5
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. florence.epron@univ-poitiers.fr.
6
Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, UFR SFA, UMR-CNRS 7285, Bât B27, 4 rue Michel Brunet, TSA 51106, 86073 Poitiers CEDEX 9, France. anthony.le.valant@univ-poitiers.fr.

Abstract

Chemisorption of hydrogen on metallic particles is often used to estimate the metal dispersion (D), the metal particle size (d), and the metallic specific surface area (SM), currently assuming a stoichiometry of one hydrogen atom H adsorbed per surface metal atom M. This assumption leads to a large error when estimating D, d, and SM, and a rigorous method is needed to tackle this problem. A model describing the statistics of the metal surface atom and site distribution on perfect cuboctahedron clusters, already developed for Pt, is applied to Pd, Ir, and Rh, using the density functional theory (DFT) calculation of the literature to determine the most favorable adsorption sites for each metal. The model predicts the H/M values for each metal, in the range 0⁻1.08 for Pd, 0⁻2.77 for Ir, and 0⁻2.31 for Rh, depending on the particle size, clearly showing that the hypothesis of H/M = 1 is not always confirmed. A set of equations is then given for precisely calculating D, d, and SM for each metal directly from the H chemisorption results determined experimentally, without any assumption about the H/M stoichiometry. This methodology provides a powerful tool for accurate determination of metal dispersion, metal particle size, and metallic specific surface area from chemisorption experiments.

KEYWORDS:

H2 chemisorption; adsorption sites; iridium; palladium; rhodium; stoichiometric factors

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