Effect of alloying on carbon formation during ethane dehydrogenation

Anne Rovik, Søren Kegnæs, Søren Dahl, Claus H. Christensen, Ib Chorkendorff

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The structure sensitivity of different transition metals in the hydrogenolysis, dehydrogenation, and coking reactions during ethane conversion has been investigated. The investigated metals, Ni, Ru, Rh, and Pd, are co-impregnated with Ag onto an inactive MgAl2O4 spinel support and tested in the conversion of ethane. A tendency is clear for all catalysts: In the first period of time 100% ethane is converted and roughly half of the carbon is converted into coke and deposited on the catalyst. The other half of the carbon is converted into methane. The active sites in the hydrogenolysis are blocked by coke during the initial period where after dehydrogenation of ethane is observed. It has previously been predicted in surface science studies that Ag covers the steps of certain transition metals. Here it is documented that the hydrogenolysis and coking reactions are significantly suppressed by co-impregnation of Ag and Ni. The effect of Ag is limited for Ru since the active sites are self-poisoned by carbon; nor for Rh/spinel is the effect observed, which is possibly due to island formation of Ag on the terraces of the Rh metal. A prolongation of the initial period with hydrogenolysis is observed for Ag-Pd/spinel due to an alloy formation of Ag and Pd at these conditions. From our results it can therefore be concluded that hydrogenolysis mainly takes place on the steps and kinks of the transition metal particles, dehydrogenation reactions mainly takes place on the terraces, and coking is significantly reduced by covering the steps sites by Ag. This important information can be used in designing new catalysts with improved selectivity and stability.
Original languageEnglish
JournalApplied Catalysis A: General
Volume358
Issue number2
Pages (from-to)269-278
ISSN0926-860X
DOIs
Publication statusPublished - 2009

Keywords

  • Coking
  • Hydrogenolysis
  • Ethane
  • Steps
  • Dehydrogenation
  • Bimetallic catalysts
  • Transition metals
  • Terraces

Cite this

Rovik, Anne ; Kegnæs, Søren ; Dahl, Søren ; Christensen, Claus H. ; Chorkendorff, Ib. / Effect of alloying on carbon formation during ethane dehydrogenation. In: Applied Catalysis A: General. 2009 ; Vol. 358, No. 2. pp. 269-278.
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abstract = "The structure sensitivity of different transition metals in the hydrogenolysis, dehydrogenation, and coking reactions during ethane conversion has been investigated. The investigated metals, Ni, Ru, Rh, and Pd, are co-impregnated with Ag onto an inactive MgAl2O4 spinel support and tested in the conversion of ethane. A tendency is clear for all catalysts: In the first period of time 100{\%} ethane is converted and roughly half of the carbon is converted into coke and deposited on the catalyst. The other half of the carbon is converted into methane. The active sites in the hydrogenolysis are blocked by coke during the initial period where after dehydrogenation of ethane is observed. It has previously been predicted in surface science studies that Ag covers the steps of certain transition metals. Here it is documented that the hydrogenolysis and coking reactions are significantly suppressed by co-impregnation of Ag and Ni. The effect of Ag is limited for Ru since the active sites are self-poisoned by carbon; nor for Rh/spinel is the effect observed, which is possibly due to island formation of Ag on the terraces of the Rh metal. A prolongation of the initial period with hydrogenolysis is observed for Ag-Pd/spinel due to an alloy formation of Ag and Pd at these conditions. From our results it can therefore be concluded that hydrogenolysis mainly takes place on the steps and kinks of the transition metal particles, dehydrogenation reactions mainly takes place on the terraces, and coking is significantly reduced by covering the steps sites by Ag. This important information can be used in designing new catalysts with improved selectivity and stability.",
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author = "Anne Rovik and S{\o}ren Kegn{\ae}s and S{\o}ren Dahl and Christensen, {Claus H.} and Ib Chorkendorff",
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Effect of alloying on carbon formation during ethane dehydrogenation. / Rovik, Anne; Kegnæs, Søren; Dahl, Søren; Christensen, Claus H.; Chorkendorff, Ib.

In: Applied Catalysis A: General, Vol. 358, No. 2, 2009, p. 269-278.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Effect of alloying on carbon formation during ethane dehydrogenation

AU - Rovik, Anne

AU - Kegnæs, Søren

AU - Dahl, Søren

AU - Christensen, Claus H.

AU - Chorkendorff, Ib

PY - 2009

Y1 - 2009

N2 - The structure sensitivity of different transition metals in the hydrogenolysis, dehydrogenation, and coking reactions during ethane conversion has been investigated. The investigated metals, Ni, Ru, Rh, and Pd, are co-impregnated with Ag onto an inactive MgAl2O4 spinel support and tested in the conversion of ethane. A tendency is clear for all catalysts: In the first period of time 100% ethane is converted and roughly half of the carbon is converted into coke and deposited on the catalyst. The other half of the carbon is converted into methane. The active sites in the hydrogenolysis are blocked by coke during the initial period where after dehydrogenation of ethane is observed. It has previously been predicted in surface science studies that Ag covers the steps of certain transition metals. Here it is documented that the hydrogenolysis and coking reactions are significantly suppressed by co-impregnation of Ag and Ni. The effect of Ag is limited for Ru since the active sites are self-poisoned by carbon; nor for Rh/spinel is the effect observed, which is possibly due to island formation of Ag on the terraces of the Rh metal. A prolongation of the initial period with hydrogenolysis is observed for Ag-Pd/spinel due to an alloy formation of Ag and Pd at these conditions. From our results it can therefore be concluded that hydrogenolysis mainly takes place on the steps and kinks of the transition metal particles, dehydrogenation reactions mainly takes place on the terraces, and coking is significantly reduced by covering the steps sites by Ag. This important information can be used in designing new catalysts with improved selectivity and stability.

AB - The structure sensitivity of different transition metals in the hydrogenolysis, dehydrogenation, and coking reactions during ethane conversion has been investigated. The investigated metals, Ni, Ru, Rh, and Pd, are co-impregnated with Ag onto an inactive MgAl2O4 spinel support and tested in the conversion of ethane. A tendency is clear for all catalysts: In the first period of time 100% ethane is converted and roughly half of the carbon is converted into coke and deposited on the catalyst. The other half of the carbon is converted into methane. The active sites in the hydrogenolysis are blocked by coke during the initial period where after dehydrogenation of ethane is observed. It has previously been predicted in surface science studies that Ag covers the steps of certain transition metals. Here it is documented that the hydrogenolysis and coking reactions are significantly suppressed by co-impregnation of Ag and Ni. The effect of Ag is limited for Ru since the active sites are self-poisoned by carbon; nor for Rh/spinel is the effect observed, which is possibly due to island formation of Ag on the terraces of the Rh metal. A prolongation of the initial period with hydrogenolysis is observed for Ag-Pd/spinel due to an alloy formation of Ag and Pd at these conditions. From our results it can therefore be concluded that hydrogenolysis mainly takes place on the steps and kinks of the transition metal particles, dehydrogenation reactions mainly takes place on the terraces, and coking is significantly reduced by covering the steps sites by Ag. This important information can be used in designing new catalysts with improved selectivity and stability.

KW - Coking

KW - Hydrogenolysis

KW - Ethane

KW - Steps

KW - Dehydrogenation

KW - Bimetallic catalysts

KW - Transition metals

KW - Terraces

U2 - 10.1016/j.apcata.2009.02.020

DO - 10.1016/j.apcata.2009.02.020

M3 - Journal article

VL - 358

SP - 269

EP - 278

JO - Applied Catalysis A: General

JF - Applied Catalysis A: General

SN - 0926-860X

IS - 2

ER -