Size-selected Metal Clusters: New Models for Catalysis with Atomic Precision

Habibpour, Vahideh; Wang, Zhi W.; Palmer, Richard E.; Heiz, Ulrich

doi:10.3923/jas.2011.1164.1170

Cited by 17 publications

(12 citation statements)

References 20 publications

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“…Heiz, Landman, together with many co-workers and collaborators, have studied cluster size effects of Pd n supported on MgO/Mo(100). 4,19,20,[43][44][45][46][47][48] This work suggests there is an increased activation barrier for O 2 dissociation with decreasing Pd n cluster size (n # 30), resulting in higher temperatures required for efficient O 2 activation. It was shown that small amounts of co-adsorbed CO can actually enhance O 2 dissociation.…”

Section: Introductionmentioning

confidence: 81%

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

2013

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A series of model catalysts were prepared by depositing different size Pd(n) clusters on alumina films grown to variable thickness on a Ta(110) support. Samples were characterized by a combination of X-ray photoelectron spectroscopy, low energy He+ scattering, and temperature-programmed reaction and desorption (TPR/ TPD). For the activity studies, the samples were first exposed to 18O2 at Tox, and then to 13CO at 180 K, where CO sticks to Pd, but not to the alumina support. CO oxidation activity increased with increasing thickness of the alumina support up to approximately 4.5 nm, but was constant for greater thicknesses. Activity increased, with Tox up to 400 K, but then declined for Tox = 500 K. Activity was also found to be non-monotonically dependent on deposited cluster size, with Pd(n) (n < or = 6) being generally more reactive than the larger clusters studied. Activity was only weakly correlated with exposed Pd binding sites, which decreased with increasing cluster size, however, there does appear to be a correlation between activity and electronic structure, as probed via the Pd 3d binding energy. Unlike previous systems we have studied, the activity of small Pd(n) on these alumina films was quite stable, with essentially no changes observed in up to eight successive TPR experiments.

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Section: Introductionmentioning

confidence: 81%

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

2013

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“…93 Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is another powerful technique for obtaining atomically resolved structural information of clusters. 119 Li et al used this method to investigate the structure of Au 309 prepared by soft-landing size-selected clusters on amorphous carbon. 120 Based on the correlation between the integrated HAADF intensity and number of atoms, the number of Au atoms in clusters was confirmed to be 309 AE 6.…”

Section: Towards Structural Characterizationmentioning

confidence: 99%

Stabilized gold clusters: from isolation toward controlled synthesis

et al. 2012

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Bare metal clusters with fewer than ∼100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of the art of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy.

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“…One reaction of this type is endothermic alkane dehydrogenation, and we have been examining carbon deposition over sub-nano Pt and Pt alloy cluster catalysts, − with the goal of stabilizing the clusters against both coking and sintering, which is a serious problem for clusters at high temperatures. In addition to maximizing the accessibility of precious metal atoms in the surface layer, sub-nano clusters often have size-dependent properties that provide additional opportunities for catalyst tuning. − Small clusters are also relatively tractable theoretically; thus, these systems allow detailed modeling of the effects of cluster physical and chemical properties on reaction mechanisms. ,− Even for a single cluster size, however, cluster reactions can be quite complex, with multiple structural isomers contributing and evolving during reactions due to thermal and adsorbate effects.…”

Section: Introductionmentioning

confidence: 99%

Coking-Resistant Sub-Nano Dehydrogenation Catalysts: Pt_nSn_x/SiO₂ (n = 4, 7)

Gorey

Zandkarimi

et al. 2020

ACS Catal.

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We present a combined experimental/theoretical study of Pt n /SiO 2 and Pt n Sn x /SiO 2 (n = 4, 7) model catalysts for the endothermic dehydrogenation of hydrocarbons, using the ethylene intermediate as a model reactant. Mass-selected Pt n clusters were deposited onto amorphous SiO 2 /Si(100) to make the Pt n SiO 2 model catalysts. To produce Pt n Sn x clusters, size-selected Pt n was used to seed selective deposition of Sn on Pt via a self-limiting H 2 / SnCl 4 /H 2 reaction sequence. Model catalysts were analyzed using C 2 D 4 and CO temperature-programmed desorption (TPD), lowenergy ion scattering (ISS), X-ray photoelectron spectroscopy (XPS), plane wave density functional theory (DFT) global optimization combined with a statistical mechanical description of the catalytic interface, and a DFT mechanistic study. Supported pure Pt n clusters are found to be highly active toward dehydrogenation of C 2 D 4 , quickly deactivating due to a combination of carbon deposition and sintering, resulting in loss of accessible Pt sites. Addition of Sn to Pt n clusters results in the complete suppression of C 2 D 4 dehydrogenation and carbon deposition and also stabilizes the clusters against thermal sintering. Theory shows that both systems have thermal access to a multitude of cluster structures and adsorbate configurations that form a statistical ensemble. While Pt 4 /SiO 2 clusters bind ethylene in both di-σ-and π-bonded configurations, Pt 4 Sn 3 /SiO 2 binds C 2 H 4 only in the π mode, with di-σ bonding suppressed by a combination of electronic and geometric features of the PtSn clusters. Dehydrogenation reaction profiles on the accessible cluster isomers were calculated using the climbing image nudged elastic band (CI-NEB) method. Dehydrogenation of diσ-bound ethylene is computed to dominate and is suppressed by Sn addition, in agreement with the experiments. DFT indicates that, after Sn alloying, the barrier for ethane-to-ethylene conversion is lower than that for unwanted ethylene dehydrogenation.

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Size-selected Metal Clusters: New Models for Catalysis with Atomic Precision

Cited by 17 publications

References 20 publications

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

Stabilized gold clusters: from isolation toward controlled synthesis

Coking-Resistant Sub-Nano Dehydrogenation Catalysts: Pt_nSn_x/SiO₂ (n = 4, 7)

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Size-selected Metal Clusters: New Models for Catalysis with Atomic Precision

Cited by 17 publications

References 20 publications

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

Stabilized gold clusters: from isolation toward controlled synthesis

Coking-Resistant Sub-Nano Dehydrogenation Catalysts: PtnSnx/SiO2 (n = 4, 7)

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Coking-Resistant Sub-Nano Dehydrogenation Catalysts: Pt_nSn_x/SiO₂ (n = 4, 7)