Carbon on Platinum Substrates: From Carbidic to Graphitic Phases on the (111) Surface and on Nanoparticles

Viñes, Francesc; Neyman, Konstantin M.; Görling, Andreas

doi:10.1021/jp903653z

Cited by 43 publications

(56 citation statements)

References 90 publications

(215 reference statements)

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“…Adsorption of CH and C on hexagonally cubic packed (hcp) sites is less stable by 10 and 15 kJ mol À1 , respectively, mainly due to steric repulsions with the Pt atom located underneath the adsorption site in the second Pt layer. [46] Moreover, the trend in the adsorption strengths is also consistent with previous slab model studies. [37,38] Furthermore, the present slab models do not introduce the sizedependence problem of the earlier small cluster models, which may lead to oscillations in adsorption energies for a given site in the range of 20-80 kJ mol…”

Section: Resultssupporting

confidence: 89%

“…The revised form of the PBE [45] (RPBE) exchange-correlation (xc) functional has been used throughout, as it has been shown to give accurate results for the adsorption of small molecules. [45,46] The transition states (TS) have been located by using the climbing-image nudged-elastic-band (CI-NEB) method connecting reactants and products adsorbed in the most stable positions. Structures near the TS have been refined by a quasi-Newton method until forces are less than 0.03 kJ mol À1 pm…”

mentioning

confidence: 99%

“…Thus, a combined calculation strategy has been applied to study bigger nanoparticles ( Figure 1) that has proven to provide a complete description in the past. [46][47][48] This strategy consists of using two complementary models; the first is a reference six-layer (3 3) PtA C H T U N G T R E N N U N G (111) slab model to describe the chemical activity and reactivity of extended terraces and the inner regions of Pt nanoparticle facets, which usually exhibit to a large degree the most stable (111) surface, corresponding to a face-centered cubic (fcc) stacking. A G-centered k-point grid of dimensions 6 6 1 has been used for the slab model.…”

mentioning

confidence: 99%

“…Further computational details on both models, PtA C H T U N G T R E N N U N G (111) slabs as well as Pt 79 clusters, can be found in a previous study. [46] It is of note, however, that boundary sites that are in contact with the oxide support have not been taken into account.…”

mentioning

confidence: 99%

“…The only possible subsequent reaction step at low hydrogen pressure is the formation of surface carbon, which is reported to occur at temperatures above 500 K. [56] The value is in line with the high value of 120 kJ mol À1 for the calculated energy barrier. At sufficiently high coverage, carbon atoms would gather to form monolayer graphene, [46] which has been detected when heating above 890 K. [73] What happens when methane dehydrogenates on Pt nanoparticles instead of extended surfaces? The role of defect sites, such as edge and corner sites, is clearly visible in the reaction profile of the Pt 79 nanoparticle in Figure 3.…”

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confidence: 99%

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Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Viñes

Lykhach

Staudt

et al. 2010

Chemistry A European J

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133

107

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Complete dehydrogenation of methane is studied on model Pt catalysts by means of state-of-the-art DFT methods and by a combination of supersonic molecular beams with high-resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH(3) and CH(2) are specially stabilized at sites located at particles edges and corners by an amount of 50-80 kJ mol(-1). This stabilization is caused by an enhanced activity of low-coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH(3) and CH(2) formation steps are endothermic on Pt(111) but markedly exothermic on Pt(79). An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol(-1) for first C-H bond scission and 40 kJ mol(-1) for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO(2) film on Cu(111). It is shown that CH(3) generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single-crystal surfaces in which CH(3) was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.

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Section: Resultssupporting

confidence: 89%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Viñes

Lykhach

Staudt

et al. 2010

Chemistry A European J

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133

107

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Template‐Assisted Formation of Fullerenes from Short‐Chain Hydrocarbons by Supported Platinum Nanoparticles

Viñes

Görling

2011

Angewandte Chemie

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Since the discovery of C 60 fullerenes, [1] research on the respective family of carbon allotropes has grown enormously, [2] mainly motivated by potential technological applications. Fullerenes are of interest in molecular electronics and for nonlinear optical devices. [3] Metal-insulator transitions of alkali-intercalated fullerenes [4] and superconductivity of alkali-doped fullerene compounds have attracted considerable scientific attention; [5] the great interest in fullerenebased materials has boosted the search for a rational design of fullerenes by new synthesis strategies. [6] Fullerenes usually are obtained by vaporization methods, [6] but can also be synthesized from polyarene precursor C 60 H 30 (1). Scott and co-workers have reported fullerene formation in the gas phase either through a series of cyclodehydrogenation steps [7] on 1 or through cyclization of a trichloroderivative, C 60 H 27 Cl 3 . [6,8] These methods, however, lead to yields below 1 %. Recently, Otero and co-workers showed that a Pt(111) single crystal surface-mediated process can achieve almost a 100 % yield, [9,10] using 1 and the precursor C 60 H 27 N 3 (2) to eventually obtain, after annealing over 750 K, fullerene and triazafullerene species. Nevertheless, the yield for the synthesis of the precursors from commercial chemicals is still only 33 % for 1 and 56 % for 2.The great improvement of the latter studies is to employ organic compounds, whose inherent geometric structure (exhibiting several interconnected C 6 and C 5 rings) and electronic structure (strong aromaticity) favor the formation of fullerenes. Inspired by this idea the following question arises: Is it possible to synthesize fullerenes from simple and abundant precursors with the help of templates, whose specific geometric and electronic structures enable a natural formation of fullerenes? This means that the formation of fullerenes is induced by specific properties of a template which acts, in addition, as a catalyst during the synthesis process. In the ideal case, the use of pertinent templates would favor the formation of specific fullerenes and, by mixing small heteroatom-containing molecules with the precursors, of heterofullerenes.Herein we show the possibility of using supported nanoparticles as templates and catalysts for the fullerene synthesis from simple precursor molecules, considering as a proof of principle, the synthesis of a simple fullerene, C 60 , from methane or ethylene by nanometer-sized platinum nanoparticles on an oxide support. By means of state-of-the-art ab initio calculations based on DFT we give arguments for the effectiveness of this set-up. For a successful fullerene synthesis sketched here, several conditions have to be fulfilled: 1) the precursor molecules have to be completely dehydrogenated at the Pt nanoparticles, releasing the hydrogen atoms as gaseous hydrogen (H 2 (g)) at working temperature, 2) C atoms or intermediate carbon compounds have to remain at the Pt nanoparticle and must not migrate to the support, and 3) the formation o...

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Template‐Assisted Formation of Fullerenes from Short‐Chain Hydrocarbons by Supported Platinum Nanoparticles

Viñes¹,

Görling²

2011

Angew Chem Int Ed

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Since the discovery of C 60 fullerenes, [1] research on the respective family of carbon allotropes has grown enormously, [2] mainly motivated by potential technological applications. Fullerenes are of interest in molecular electronics and for nonlinear optical devices.[3] Metal-insulator transitions of alkali-intercalated fullerenes [4] and superconductivity of alkali-doped fullerene compounds have attracted considerable scientific attention; [5] the great interest in fullerenebased materials has boosted the search for a rational design of fullerenes by new synthesis strategies. [6] Fullerenes usually are obtained by vaporization methods, [6] but can also be synthesized from polyarene precursor C 60 H 30 (1). Scott and co-workers have reported fullerene formation in the gas phase either through a series of cyclodehydrogenation steps [7] on 1 or through cyclization of a trichloroderivative, C 60 H 27 Cl 3 . [6,8] These methods, however, lead to yields below 1 %. Recently, Otero and co-workers showed that a Pt(111) single crystal surface-mediated process can achieve almost a 100 % yield, [9,10] using 1 and the precursor C 60 H 27 N 3 (2) to eventually obtain, after annealing over 750 K, fullerene and triazafullerene species. Nevertheless, the yield for the synthesis of the precursors from commercial chemicals is still only 33 % for 1 and 56 % for 2.The great improvement of the latter studies is to employ organic compounds, whose inherent geometric structure (exhibiting several interconnected C 6 and C 5 rings) and electronic structure (strong aromaticity) favor the formation of fullerenes. Inspired by this idea the following question arises: Is it possible to synthesize fullerenes from simple and abundant precursors with the help of templates, whose specific geometric and electronic structures enable a natural formation of fullerenes? This means that the formation of fullerenes is induced by specific properties of a template which acts, in addition, as a catalyst during the synthesis process. In the ideal case, the use of pertinent templates would favor the formation of specific fullerenes and, by mixing small heteroatom-containing molecules with the precursors, of heterofullerenes.Herein we show the possibility of using supported nanoparticles as templates and catalysts for the fullerene synthesis from simple precursor molecules, considering as a proof of principle, the synthesis of a simple fullerene, C 60 , from methane or ethylene by nanometer-sized platinum nanoparticles on an oxide support. By means of state-of-the-art ab initio calculations based on DFT we give arguments for the effectiveness of this set-up. For a successful fullerene synthesis sketched here, several conditions have to be fulfilled: 1) the precursor molecules have to be completely dehydrogenated at the Pt nanoparticles, releasing the hydrogen atoms as gaseous hydrogen (H 2 (g)) at working temperature, 2) C atoms or intermediate carbon compounds have to remain at the Pt nanoparticle and must not migrate to the support, and 3) the formation of...

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Carbon on Platinum Substrates: From Carbidic to Graphitic Phases on the (111) Surface and on Nanoparticles

Cited by 43 publications

References 90 publications

Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Template‐Assisted Formation of Fullerenes from Short‐Chain Hydrocarbons by Supported Platinum Nanoparticles

Template‐Assisted Formation of Fullerenes from Short‐Chain Hydrocarbons by Supported Platinum Nanoparticles

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