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Supra‐monolayer coverages on small metal clusters and their effects on H 2 chemisorption particle size estimates
Author(s) -
Almithn Abdulrahman S.,
Hibbitts David D.
Publication year - 2018
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.16110
Subject(s) - chemisorption , monolayer , hydrogen , metal , chemistry , particle size , stoichiometry , adsorption , saturation (graph theory) , particle (ecology) , analytical chemistry (journal) , crystallography , chemical physics , organic chemistry , biochemistry , oceanography , mathematics , combinatorics , geology
H 2 chemisorption measurements are used to estimate the size of supported metal particles, often using a hydrogen‐to‐surface‐metal stoichiometry of unity. This technique is most useful for small particles whose sizes are difficult to estimate through electron microscopy or X‐ray diffraction. Undercoordinated metal atoms at the edges and corners of particles, however, make up large fractions of small metal clusters, and can accommodate multiple hydrogen atoms leading to coverages which exceed 1 ML (supra‐monolayer). Density functional theory was used to calculate hydrogen adsorption energies on Pt and Ir particles (38–586 atoms, 0.8–2.4 nm) at high coverages (≤3.63 ML). Calculated differential binding energies confirm that Pt and Ir (111) single‐crystal surfaces saturate at 1 ML; however, Pt and Ir clusters saturate at supra‐monolayer coverages as large as 2.9 ML. Correlations between particle size and saturation coverage are provided that improve particle size estimates from H 2 chemisorption for Pt‐group metals. © 2018 American Institute of Chemical Engineers AIChE J , 64: 3109–3120, 2018