Computational study of the adsorption of benzene and hydrogen on palladium–iridium nanoalloys

Davis, Jack B. A.; Horswell, Sarah L.; Piccolo, L.; Johnston, Roy L.

doi:10.1016/j.jorganchem.2015.04.033

Cited by 10 publications

(11 citation statements)

References 39 publications

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“…Moreover, unlike Pd nanoparticles, PdIr nanoalloys do not form a β -hydride phase. Consistently with previous TEM-EDX analyzes which have suggested a surface enrichment in Pd 6 , computational simulations for small clusters 10 and 2 nm-sized particles 11 predict various chemical configurations mostly driven by a strong surface segregation of Pd and the large miscibility gap of bulk PdIr, which has profound consequences on surface reactivity 12,13 .…”

Section: Introductionsupporting

confidence: 82%

“…In this context, until now, the most advanced work on PdIr is based on DFT calculations performed on small clusters containing 13 to 79 atoms. Both structural and adsorption studies have been carried out, the latter involving benzene, hydrogen and carbon monoxide molecules 10,12,13 . Although these studies show some nanosize effects both on the atomic structure and the reactivity, larger size nanoparticles are hardly handleable within first-principle calculations.…”

Section: Introductionmentioning

confidence: 99%

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How the hydrogen sorption properties of palladium are modified through interaction with iridium

Goyhenex

Piccolo

2017

Phys. Chem. Chem. Phys.

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Hydrogen sorption (adsorption/absorption) in metals, in the form of thin films or nanoparticles, is a key process in the fields of energy storage and heterogeneous catalysis. Atomic hydrogen dissolved in the subsurface of a metal affects its surface atomic and electronic structures, and thereby its surface reactivity and catalytic properties. In addition, alloy effects modify both catalytic and hydrogen sorption phenomena. In order to rationalize recent experimental results showing the negative impact of hydrogen absorption on catalysis, the present article proposes an insight into structure-reactivity relationships through computational simulations, using density functional theory, of hydrogen sorption in the near-surface region of palladium atomic layers interacting with an iridium substrate. A detailed analysis of the electronic structure using local projected densities of states (PDOS) and crystal orbital overlap population (COOP) curves was carried out. It is found that the Pd/Ir system, with respect to pure Pd surfaces, keeps acceptable adsorption properties for surface reactions while preventing hydrogen penetration. The results of electronic structure calculations show that the most important difference between Pd and Ir is related to the strong anti-bonding character of the 1s-H/5p-Ir interaction, leading to the non-bonding character of the sp-Ir interaction with hydrogen. Thus, increasing the Ir concentration in a Pd-based system increases the anti-bonding contribution, which strongly weakens the overall metal-hydrogen interaction.

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Section: Introductionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

How the hydrogen sorption properties of palladium are modified through interaction with iridium

Goyhenex

Piccolo

2017

Phys. Chem. Chem. Phys.

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“…For the reason of energetic considerations, hydrogen adsorption sites differ from one metal to another. Ab initio and/or DFT calculations obtained from the literature for Pd, Ir, and Rh [ 30 , 31 , 32 , 33 , 34 , 35 ] are therefore used to firstly determine the most favorable adsorption sites, which are evolving with the cluster size. The latter are finally used to build a unique adsorption repetitive sequence for each metal based on a linear combination of these adsorption sites to finally describe the hydrogen adsorption in the full size range.…”

Section: Model Calculationmentioning

confidence: 99%

“…This raises the question about the nature of adsorption sites between supported and unsupported particles, and also, about the accessibility of a hydrogen atom over the whole metallic surface when a strong metal support interaction (SMSI) occurs. One may reasonably consider that adsorption sites are not modified by the presence of a support, since it has been demonstrated for Ir that top and bridge sites are the most favorable adsorption sites, whether the metal particle is supported [ 34 ] or not [ 31 , 33 ]. Next, concerning the fraction of metal interacting with the support, the metal support interaction is weakened when H/M ratio increases [ 36 ].…”

Section: Model Calculationmentioning

confidence: 99%

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

et al. 2018

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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.

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“…23,24 Pd-Ir nanoalloys are often used as catalysts in the preferential oxidation of CO (PROX). 8,10 The Pd-Ir system has rarely been studied computationally, [25][26][27][28][29] and relatively few catalytic studies have been devoted to Pd-Ir nanoalloys. 9,27,30 In this study, the structure and chemical ordering of bare and CO-adsorbed Pd-Ir nanoalloys have been investigated theoretically by using density functional theory (DFT).…”

Section: Introductionmentioning

confidence: 99%

DFT study of the structure, chemical ordering and molecular adsorption of Pd–Ir nanoalloys

Fan

Demiroğlu

Hussein

et al. 2017

Phys. Chem. Chem. Phys.

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The structures and surface adsorption sites of Pd-Ir nanoalloys are crucial to the understanding of their catalytic performance because they can affect the activity and selectivity of nanocatalysts. In this article, density functional theory (DFT) calculations are performed on bare Pd-Ir nanoalloys to systematically explore their stability and chemical ordering properties, before studying the adsorption of CO on the nanoalloys. First, the structural stability of 38-atom and 79-atom truncated octahedral (TO) Pd-Ir nanoalloys are investigated. Then the adsorption properties and preferred adsorption sites of CO on 38-atom Pd-Ir nanoalloys are considered. The PdIr structure, which has the lowest energy of all the considered isomers, exhibits the highest structural stability, while the PdIr configuration is the least stable. In addition, the adsorption strength of CO on Ir atoms is found to be greater than on Pd for Pd-Ir nanoclusters. The preferred adsorption sites of CO on pure Pd and Ir clusters are in agreement with calculations and experiments on extended Pd and Ir surfaces. In addition, d-band center and charge effects on CO adsorption strength on Pd-Ir nanoalloys are analyzed by comparison with pure clusters. The study provides a valuable theoretical insight into catalytically active Pd-Ir nanoalloys.

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Computational study of the adsorption of benzene and hydrogen on palladium–iridium nanoalloys

Cited by 10 publications

References 39 publications

How the hydrogen sorption properties of palladium are modified through interaction with iridium

How the hydrogen sorption properties of palladium are modified through interaction with iridium

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

DFT study of the structure, chemical ordering and molecular adsorption of Pd–Ir nanoalloys

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