Reactivity of Ethyl Groups on a Sn/Pt(111) Surface Alloy

Zhao, Haibo; Koel, Bruce E.

doi:10.1007/s10562-004-0772-6

Cited by 10 publications

(13 citation statements)

References 55 publications

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“…Computationally, density functional theory (DFT) has been a useful tool for explaining trends in the experimental data in light alkane dehydrogenation. DFT calculations of decreased alkene binding energy PtSn alloys as compared to those of pure Pt − are in good agreement with experimental measurements. − ,− DFT has shown evidence that coke formation precursors on Pt(111) are likely formed through the C–C bond cleavage of alkynes, which is highly unfavored on PtSn alloys . In addition, the activation energy barrier for ethene and propylene dehydrogenation, are higher on PtSn alloys than on the alkene desorption step, which leads to higher alkene selectivity and less coke formation due to alkene dehydrogenation.…”

Section: Introductionsupporting

confidence: 64%

Predicting Selectivity for Ethane Dehydrogenation and Coke Formation Pathways over Model Pt–M Surface Alloys with ab Initio and Scaling Methods

Hook

Celik

2017

J. Phys. Chem. C

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The effects of alloying platinum with transition and post-transition metals on the kinetics and thermodynamics of dehydrogenation and coke formation pathways during light alkane dehydrogenation have been studied using density functional theory. Supported Pt catalysts are known to be active for light alkane dehydrogenation, but the high temperatures required by these endothermic reactions leads to significant coke formation and deactivation. A limited set of Pt alloys have been investigated experimentally previously, with decreases coke formation and deactivation. Using periodic density functional theory, we have investigated a wider range of Pt-alloy compositions, including metals from groups 7–15, to better understand the reduction in surface carbon formation and enhanced selectivity during ethane dehydrogenation. The post-transition metal alloys show the greatest ability to decrease the binding energy of carbonaceous species. At low alloy coverage (1/4 ML), these elements affect binding energies primarily through electronic effects, leaving binding geometries unaltered. A scaling relation was developed between simple CH x species and the barriers for ethene reactions to predict selectivity for ethene desorption vs dehydrogenation. At higher alloy coverage (1/2 ML), geometric effects play an important role in surface–adsorbate interactions. There is no global optimum alloying element, rather the best alloy depends on the alloy coverage. PtPb and PtSb show the most promise at low and high alloy coverages, respectively. However, this work predicts that PtSn is the prevailing industrial catalyst because it shows good performance for both alloy coverages, an important property when synthetic control over precise alloy ratio in each metal particle is difficult or impractical to attain.

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Section: Introductionsupporting

confidence: 64%

Predicting Selectivity for Ethane Dehydrogenation and Coke Formation Pathways over Model Pt–M Surface Alloys with ab Initio and Scaling Methods

Hook

Celik

2017

J. Phys. Chem. C

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“…Density functional theory (DFT) has been used to provide fundamental insight into the properties and catalyst function of alkane dehydrogenation catalysts. DFT calculations confirm that the adsorption energy for alkenes is less on platinum–tin alloys as compared to pure Pt, − in good agreement with experiment. − Stepped sites on Pt(211) are more active than Pt(211) or Pt (111) terraces, but are also less selective toward the alkene in ethane dehydrogenation , and propane dehydrogenation . Undercoordinated step and edge sites have also been implicated in methane activation on Pt .…”

Section: Introductionsupporting

confidence: 63%

“…Supported Pt particles are the preferred catalysts for light alkane dehydrogenation. ,, Pt is the most active pure metal for light alkane dehydrogenation and shows high selectivity at short reaction times. The alkenes formed from dehydrogenation bind strongly to the Pt surface, making desorption difficult and facilitating subsequent further dehydrogenation or C–C bond cleavage–leading to the formation of carbonaceous surface species. − Consequently, catalyst deactivation is rapid and correlates with large deposits of coke.…”

Section: Introductionmentioning

confidence: 99%

“…Reductions in both catalyst deactivation and coke formation relative to pure Pt have been achieved by alloying Pt with Sn. ,− Alloying with Sn weakens the interaction of the alkenes with the alloy surface, which allows the product to desorb from the catalyst surface more readily as compared to pure Pt. − The rates of further dehydrogenation and C–C bond cleavage are reduced as a result as desorption of the alkene competes with dissociation. However, the activation energy barriers for dehydrogenation of ethyl radicals (derived from ethane) to revert to ethane doubled on platinum–tin alloys as compared to pure Pt, so a reduction of activity may be expected over the alloys. Deactivation was reduced by 60% for ethene dehydrogenation relative to pure Pt by alloying with Sn while total carbon formation was reduced by 50% .…”

Section: Introductionmentioning

confidence: 99%

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Effect of Tin Coverage on Selectivity for Ethane Dehydrogenation over Platinum–Tin Alloys

2016

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Periodic, self-consistent generalized gradient approximation (GGA PW-91) density functional theory (DFT) was applied to study the effect of tin coverage in platinum–tin alloys in the dehydrogenation of ethane. Light alkane dehydrogenation to olefins can add significant value to hydrocarbon processes that generate ethane and propane by converting low value commodity fuels to high-value chemical and polymer precursors. Supported Pt catalysts are known to be active but show significant coke formation and deactivation, which can be reduced by alloying with Sn. Model surfaces of substitutional surface alloys of Pt and Sn were constructed with 1/4 and 1/2 of a monolayer of Pt atoms in the surface of fcc Pt(111) replaced by Sn atoms. Potential energy surfaces for all C1 and C2 derivatives from C–H and C–C bond cleavage from ethane were computed with kinetic reaction barriers obtained using the climbing-image nudged elastic band method. While the presence of Sn weakened the binding energies of all species, the effect for low Sn coverage was purely an electronic effect as binding geometries were unchanged relative to those on Pt(111). At higher Sn coverage, the elimination of 3-fold hollow sites consisting of Pt-atom nearest neighbors resulted in geometric changes in binding geometries and larger effects on the reaction and activation energies than the purely electronic effect observed at lower Sn coverage. The experimentally observed reduction in deactivation with H2 cofeed arose due to competition between H atoms and ethene for binding sites whereby ethene was forced to desorb from the surface at moderate hydrogen coverages. Pathways to the formation of atomic carbon were compared on the alloys, and while atomic carbon may play a role in coke formation on pure Pt, it is unlikely to be relevant in coke formation over the alloys.

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“…Supported Pt alloy nanoparticles have also been utilized as active catalysts in a wide range of catalytic reactions due to the positive electronic (ligand) effect, geometric (ensemble) effect, strain effect, isolation effect, and synergistic effect, etc. 41 Typically, Sn promotes Pt catalysis for selective hydrogenation/dehydrogenation, [42][43][44][45][46][47][48][49][50][51][52][53][54][55] oxidative hydrocarbon reforming, 46,50,[55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] and fuel cell operation, 4,[72][73][74] etc. [75][76][77][78][79] Nevertheless, the active alloy phases easily collapse into each metal oxide under ambient oxygen, resulting in a decrease in the catalytic performances.…”

Section: Introductionmentioning

confidence: 99%

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

Uemura

Inada

Bando

et al. 2011

Phys. Chem. Chem. Phys.

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The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.

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Reactivity of Ethyl Groups on a Sn/Pt(111) Surface Alloy

Cited by 10 publications

References 55 publications

Predicting Selectivity for Ethane Dehydrogenation and Coke Formation Pathways over Model Pt–M Surface Alloys with ab Initio and Scaling Methods

Predicting Selectivity for Ethane Dehydrogenation and Coke Formation Pathways over Model Pt–M Surface Alloys with ab Initio and Scaling Methods

Effect of Tin Coverage on Selectivity for Ethane Dehydrogenation over Platinum–Tin Alloys

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

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