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

Alec Hook; Jacob D. Massa; Fuat E. Celik

doi:https://doi.org/10.1021/acs.jpcc.6b08407

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

Alec Hook, Jacob D. Massa, Fuat E. Celik

Engn - Chem & Biochem Engn

Rutgers, The State University

Research output: Contribution to journal › Article › peer-review

28 Scopus citations

Abstract

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. (Graph Presented).

Original language	English (US)
Pages (from-to)	27307-27318
Number of pages	12
Journal	Journal of Physical Chemistry C
Volume	120
Issue number	48
DOIs	https://doi.org/10.1021/acs.jpcc.6b08407
State	Published - Dec 8 2016

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Energy(all)
Physical and Theoretical Chemistry
Surfaces, Coatings and Films

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title = "Effect of Tin Coverage on Selectivity for Ethane Dehydrogenation over Platinum-Tin Alloys",

abstract = "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. (Graph Presented).",

author = "Alec Hook and Massa, {Jacob D.} and Celik, {Fuat E.}",

note = "Funding Information: This work was supported by the National Science Foundation under grant number DGE-0903675. Publisher Copyright: {\textcopyright} 2016 American Chemical Society.",

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AU - Hook, Alec

AU - Massa, Jacob D.

AU - Celik, Fuat E.

PY - 2016/12/8

Y1 - 2016/12/8

N2 - 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. (Graph Presented).

AB - 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. (Graph Presented).

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JF - Journal of Physical Chemistry C

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

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