IrPd nanoalloys: simulations, from surface segregation to local electronic properties

Andriamiharintsoa, Tsiky Hasiniaina; Rakotomahevitra, A.; Piccolo, L.; Goyhenex, C.

doi:10.1007/s11051-015-3020-7

Cited by 10 publications

(5 citation statements)

References 40 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%

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%

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

Goyhenex

Piccolo

2017

Phys. Chem. Chem. Phys.

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“…Beyond downsizing, nanoalloying is an additional way of boosting the hydrogen absorption capacity, as shown for Pd-Pt and Ag-Rh systems [160]. In contrast, we have found that nanoalloying Pd with Ir strongly decreases the hydrogen absorption capacity of Pd and suppresses β hydriding [161,162] through the formation of a core-shell Ir@Pd structure (Figure 7, left-hand side) [163,164]. The decreased hydrogen capacity is correlated to a strongly increased preferential CO oxidation activity in the presence of H 2 (PROX process) with respect to pure Pd and Ir counterparts [161,165].…”

Section: Hydrogen Absorption and Hydridingmentioning

confidence: 73%

Restructuring effects of the chemical environment in metal nanocatalysis and single-atom catalysis

Piccolo

2021

Catalysis Today

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Metal-based heterogeneous catalysts mostly consist of supported nanoparticles of a few nanometers in size, because these objects provide a good compromise between exposed active surface area and structural stability. However, far from being static, heterogeneous catalysts constantly evolve under reaction conditions, thereby creating and removing surface sites in response to their gaseous or liquid reactive environment. Modern ex situ and in situ investigations have shown that nanocatalysts at work can face a number of deep restructuring phenomena, such as morphological change, compound formation, segregation, leaching, as well as redispersion and other metal-support interaction effects. Recently emerging single-atom catalysts are -like subnanometric clusters -especially sensitive to their chemical environment. Using examples from the recent literature with a particular emphasis on operando characterization studies, this article reviews the main dynamic effects induced by the reaction medium on nanocatalysts (including nanoalloy catalysts) and single-atom catalysts.

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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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IrPd nanoalloys: simulations, from surface segregation to local electronic properties

Cited by 10 publications

References 40 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

Restructuring effects of the chemical environment in metal nanocatalysis and single-atom catalysis

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

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