Effective coordination as a predictor of adsorption energies: A model study of NO on Rh(100) and Rh/MgO(100) surfaces

Pushpa, Raghani; Ghosh, Prasenjit; Narasimhan, Shobhana; Gironcoli, Stefano de

doi:10.1103/physrevb.79.165406

Cited by 10 publications

(10 citation statements)

References 32 publications

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“…Figure 10b shows a comparison of E ads on the three surfaces; detailed data are given in Table S1 of the Supporting Information. Rh(100) had generally the smallest E ads , whereas Rh 38 had the greatest, which we attribute to the low-coordinated Rh atoms on the Rh 38 surface having a higher d-band center 87 and being more active. The slightly increased E ads value on Rh(100) e corresponds to the expanded lattice.…”

Section: Resultsmentioning

confidence: 80%

Dependence on Size of Supported Rh Nanoclusters in the Decomposition of Methanol

Hung

Liao

et al. 2015

ACS Catal.

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The decomposition of methanol catalyzed with Rh nanoclusters supported on an ordered thin film of Al2O3/NiAl(100) became enhanced on decreasing the size of the clusters. The decomposition of methanol (and methanol-d 4) proceeded through dehydrogenation; the formation thereby of CO became evident above 200 K, depending little on the cluster size. In contrast, the production of CO and hydrogen (deuterium) from the reaction varied notably with the cluster size. The quantity of either CO or hydrogen produced per Rh surface site was unaltered on clusters of diameter >1.5 nm and height >0.6 nm, corresponding to about 65% of methanol undergoing decomposition on adsorption in a monolayer on the clusters. For clusters of diameter <1.5 nm and height <0.6 nm, the production per Rh surface site increased with decreasing size, up to 4 times that on the large clusters or Rh(100) single-crystal surface. The reactivity was enhanced largely because, with decreasing cluster size, the activation energy for the scission of the O–H bond in the initial dehydrogenation became smaller than the activation energy for the competing desorption. The property was associated with the edge Rh atoms at the surface of small clusters.

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Section: Resultsmentioning

confidence: 80%

Dependence on Size of Supported Rh Nanoclusters in the Decomposition of Methanol

Hung

Liao

et al. 2015

ACS Catal.

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“…These are the same systems for which we had earlier computed adsorption energies. 5 We note that systems ͑a͒ and ͑b͒ are related by strain, as are systems ͑c͒ and ͑d͒, while systems ͑a͒ and ͑c͒, and systems ͑b͒ and ͑d͒, differ only in the chemical nature of the substrate. Only system ͑a͒ may be "real"systems ͑b͒ and ͑c͒ are hypothetical while it is not known whether system ͑d͒ corresponds to a realistic experimental structure.…”

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confidence: 94%

“…We note that all the above calculational details are identical to those used in our earlier work on adsorption. 5 In order to test the performance of the pseudopotentials used by us, we first calculated the bulk lattice parameters of Rh and MgO and the N-O bond length in gas phase and compare the results with experimental measurements and previous calculations. We obtained a value of 3.85 Å for the lattice constant of bulk Rh, which is in excellent agreement with the experimental value of 3.80 Å, 11 and previous theoretical values of 3.87 Å.…”

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confidence: 99%

“…18͒ and adsorption energies of NO on Rh. 5 The effective coordination number serves as a measure of the ambient electronic density ͑from other, neighboring at-oms͒ that a surface Rh atom is embedded in. It takes into account the local environment of the surface Rh atom by incorporating information about which chemical species the neighbors are, as well as how far away they are.…”

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confidence: 99%

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Effective coordination number: A simple indicator of activation energies for NO dissociation on Rh(100) surfaces

et al. 2009

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We have used density-functional theory to compute the activation energy for the dissociation of NO on two physical and two hypothetical systems: unstrained and strained Rh͑100͒ surfaces and monolayers of Rh atoms on strained and unstrained MgO͑100͒ surfaces. We find that the activation energy, relative to the gas phase, is reduced when a monolayer of Rh is placed on MgO, due both to the chemical nature of the substrate and the strain imposed by the substrate. The former effect is the dominant one, though both effects are of the same order of magnitude. We find that both effects are encapsulated in a simple quantity which we term as the "effective coordination number" ͑n e ͒; the activation energy is found to vary linearly with n e . We have compared the performance of n e as a predictor of activation energy of NO dissociation on the above-mentioned Rh surfaces with the two well-established indicators, namely, the position of the d-band center and the coadsorption energy of N and O. We find that for the present systems n e performs as well as the other two indicators.Catalysts are vital to the present-day chemical industry and are also important in the search for alternative and cleaner energy sources. However, most catalysts that are in use today have been developed by a process of trial and error, and replacing this by a program of rational design is one of the grand challenges in chemistry today. Theoretical calculations using density-functional theory ͑DFT͒ can help provide insight and guiding principles since they can supply detailed microscopic information about the various elementary steps in a reaction. 1 They also allow one to explore hypothetical systems that, even if impossible to create in the laboratory, can help one to discern patterns that can then provide guidelines for the design process.In this Brief Report, we focus on one particular reaction: the dissociation of NO, which is one of the steps in converting undesirable NO x gases to N 2 , for example, in catalytic converters in automobiles; Rh has been shown to be one of the best catalysts for this process. [2][3][4] In catalytic converters, small particles of the metal catalyst are placed on a ceramic substrate. This situation is quite different from the ideal and clean single-crystal metal surfaces that have traditionally been studied using the techniques of surface science. In recent years, however, there has been increasing attention paid to more realistic situations, such as the presence of asperities and defects, finite particle sizes, and the influence of the substrate. The substrate can affect the operation of a catalyst in various ways since it changes the environment of the metal catalyst atoms: they can have different neighbors, and may also be strained due to the presence of the substrate.Here we consider four model systems that enable us to explore the effects of changing the local environment of catalyst atoms: ͑a͒ a Rh͑100͒ surface, ͑b͒ a Rh͑100͒ surface where both the surface and substrate have been stretched ͑by 9.9%͒ to the larg...

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“…Rhodium’s importance as a catalytic agent has led to numerous density functional theory (DFT) studies of its surface and nanoparticle properties. − Recent increased interest in intermetallic catalysts led to preliminary studies of a few PGM alloys and surface alloys − that clarified the need to evaluate the stability of new potential alloy catalysts. However, investigations of rhodium binary systems are less common.…”

Section: Introductionmentioning

confidence: 99%

The New Face of Rhodium Alloys: Revealing Ordered Structures from First Principles

et al. 2009

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The experimental and computational data on rhodium binary alloys is sparse despite its importance in numerous applications, especially as an alloying agent in catalytic materials. Half of the Rh-transition metal systems (14 out of 28) are reported to be phase separating or are lacking experimental data. Comprehensive high-throughput first-principles calculations predict stable ordered structures in 9 of those 14 binary systems. They also predict a few unreported compounds in the known compound-forming systems. These results indicate the need for an extensive revision of our current understanding of Rh alloys through a combination of theoretical predictions and experimental validations.

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Effective coordination as a predictor of adsorption energies: A model study of NO on Rh(100) and Rh/MgO(100) surfaces

Cited by 10 publications

References 32 publications

Dependence on Size of Supported Rh Nanoclusters in the Decomposition of Methanol

Dependence on Size of Supported Rh Nanoclusters in the Decomposition of Methanol

Effective coordination number: A simple indicator of activation energies for NO dissociation on Rh(100) surfaces

The New Face of Rhodium Alloys: Revealing Ordered Structures from First Principles

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