Deactivating Carbon Formation on a Ni/Al2O3 Catalyst under Methanation Conditions

Sine Ellemann Olesen, Klas J. Andersson, Christian Danvad Damsgaard, Ib Chorkendorff

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The carbon formation causing deactivation during CO methanation was studied for a Ni/Al2O3 catalyst. Sulfur-free methanation at low temperature (573 K) for various lengths of time was followed by temperature-programmed hydrogenation (TPH) providing information on carbon types involved in the deactivation of the catalyst.Three main carbon hydrogenation peaks were evident from TPHs following methanation: ∼460, ∼650, and ∼775 K. It is suggested that the ∼460 K TPH peak was composed of two peaks: a surface carbide peak at 445–460 K, and a peak due to carbon dissolved into the nickel at 485 K based on CO and CH4 adsorption measurements and XRD analysis. The 650 and 775 K temperature peaks are assigned to polymerized carbon structures and the ∼775K peak was found to be the primary cause of deactivation as judged by a linear correlation between its amount and the degree of catalyst deactivation. The longer the duration of the methanation test, the more carbon was built up on the Ni surfaces and the highest observed amount was quantified to be as much as eight carbon atoms per Ni surface atom (8 C/Nisurf), which would roughly correspond to an average coverage of four monolayers of graphene. From H2 desorption measurements after reaction the 650 K TPH peak carbon structure is proposed to be partially hydrogenated, possibly resembling polycyclic aromatic-like carbon. The 775 K peak carbon species are likely more graphene-like. Results indicate that although carbon deposition nucleation may be initiated at the most active methanation sites,i.e., the Ni step sites, subsequent growth takes place over Ni terracesites. A strongly inhomogeneous carbon growth distribution over the Ni nanoparticle surfaces could also account for our findings. Similarto suggestions regarding catalyst deactivation in Fischer–Tropschsynthesis, a surface CH* coupling mechanism is likely taking place,and our results suggest these polymeric hydrocarbon species become more ordered, aromatic, and eventually graphene-like over time.
Original languageEnglish
JournalJournal of Physical Chemistry C
Volume121
Issue number29
Pages (from-to)15556-15564
Number of pages9
ISSN1932-7447
DOIs
Publication statusPublished - 2017

Cite this

@article{40f504759ae949d2b5837de9fc27ca5d,
title = "Deactivating Carbon Formation on a Ni/Al2O3 Catalyst under Methanation Conditions",
abstract = "The carbon formation causing deactivation during CO methanation was studied for a Ni/Al2O3 catalyst. Sulfur-free methanation at low temperature (573 K) for various lengths of time was followed by temperature-programmed hydrogenation (TPH) providing information on carbon types involved in the deactivation of the catalyst.Three main carbon hydrogenation peaks were evident from TPHs following methanation: ∼460, ∼650, and ∼775 K. It is suggested that the ∼460 K TPH peak was composed of two peaks: a surface carbide peak at 445–460 K, and a peak due to carbon dissolved into the nickel at 485 K based on CO and CH4 adsorption measurements and XRD analysis. The 650 and 775 K temperature peaks are assigned to polymerized carbon structures and the ∼775K peak was found to be the primary cause of deactivation as judged by a linear correlation between its amount and the degree of catalyst deactivation. The longer the duration of the methanation test, the more carbon was built up on the Ni surfaces and the highest observed amount was quantified to be as much as eight carbon atoms per Ni surface atom (8 C/Nisurf), which would roughly correspond to an average coverage of four monolayers of graphene. From H2 desorption measurements after reaction the 650 K TPH peak carbon structure is proposed to be partially hydrogenated, possibly resembling polycyclic aromatic-like carbon. The 775 K peak carbon species are likely more graphene-like. Results indicate that although carbon deposition nucleation may be initiated at the most active methanation sites,i.e., the Ni step sites, subsequent growth takes place over Ni terracesites. A strongly inhomogeneous carbon growth distribution over the Ni nanoparticle surfaces could also account for our findings. Similarto suggestions regarding catalyst deactivation in Fischer–Tropschsynthesis, a surface CH* coupling mechanism is likely taking place,and our results suggest these polymeric hydrocarbon species become more ordered, aromatic, and eventually graphene-like over time.",
author = "Olesen, {Sine Ellemann} and Andersson, {Klas J.} and Damsgaard, {Christian Danvad} and Ib Chorkendorff",
year = "2017",
doi = "10.1021/acs.jpcc.7b03754",
language = "English",
volume = "121",
pages = "15556--15564",
journal = "The Journal of Physical Chemistry Part C",
issn = "1932-7447",
publisher = "American Chemical Society",
number = "29",

}

Deactivating Carbon Formation on a Ni/Al2O3 Catalyst under Methanation Conditions. / Olesen, Sine Ellemann; Andersson, Klas J.; Damsgaard, Christian Danvad; Chorkendorff, Ib.

In: Journal of Physical Chemistry C, Vol. 121, No. 29, 2017, p. 15556-15564.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Deactivating Carbon Formation on a Ni/Al2O3 Catalyst under Methanation Conditions

AU - Olesen, Sine Ellemann

AU - Andersson, Klas J.

AU - Damsgaard, Christian Danvad

AU - Chorkendorff, Ib

PY - 2017

Y1 - 2017

N2 - The carbon formation causing deactivation during CO methanation was studied for a Ni/Al2O3 catalyst. Sulfur-free methanation at low temperature (573 K) for various lengths of time was followed by temperature-programmed hydrogenation (TPH) providing information on carbon types involved in the deactivation of the catalyst.Three main carbon hydrogenation peaks were evident from TPHs following methanation: ∼460, ∼650, and ∼775 K. It is suggested that the ∼460 K TPH peak was composed of two peaks: a surface carbide peak at 445–460 K, and a peak due to carbon dissolved into the nickel at 485 K based on CO and CH4 adsorption measurements and XRD analysis. The 650 and 775 K temperature peaks are assigned to polymerized carbon structures and the ∼775K peak was found to be the primary cause of deactivation as judged by a linear correlation between its amount and the degree of catalyst deactivation. The longer the duration of the methanation test, the more carbon was built up on the Ni surfaces and the highest observed amount was quantified to be as much as eight carbon atoms per Ni surface atom (8 C/Nisurf), which would roughly correspond to an average coverage of four monolayers of graphene. From H2 desorption measurements after reaction the 650 K TPH peak carbon structure is proposed to be partially hydrogenated, possibly resembling polycyclic aromatic-like carbon. The 775 K peak carbon species are likely more graphene-like. Results indicate that although carbon deposition nucleation may be initiated at the most active methanation sites,i.e., the Ni step sites, subsequent growth takes place over Ni terracesites. A strongly inhomogeneous carbon growth distribution over the Ni nanoparticle surfaces could also account for our findings. Similarto suggestions regarding catalyst deactivation in Fischer–Tropschsynthesis, a surface CH* coupling mechanism is likely taking place,and our results suggest these polymeric hydrocarbon species become more ordered, aromatic, and eventually graphene-like over time.

AB - The carbon formation causing deactivation during CO methanation was studied for a Ni/Al2O3 catalyst. Sulfur-free methanation at low temperature (573 K) for various lengths of time was followed by temperature-programmed hydrogenation (TPH) providing information on carbon types involved in the deactivation of the catalyst.Three main carbon hydrogenation peaks were evident from TPHs following methanation: ∼460, ∼650, and ∼775 K. It is suggested that the ∼460 K TPH peak was composed of two peaks: a surface carbide peak at 445–460 K, and a peak due to carbon dissolved into the nickel at 485 K based on CO and CH4 adsorption measurements and XRD analysis. The 650 and 775 K temperature peaks are assigned to polymerized carbon structures and the ∼775K peak was found to be the primary cause of deactivation as judged by a linear correlation between its amount and the degree of catalyst deactivation. The longer the duration of the methanation test, the more carbon was built up on the Ni surfaces and the highest observed amount was quantified to be as much as eight carbon atoms per Ni surface atom (8 C/Nisurf), which would roughly correspond to an average coverage of four monolayers of graphene. From H2 desorption measurements after reaction the 650 K TPH peak carbon structure is proposed to be partially hydrogenated, possibly resembling polycyclic aromatic-like carbon. The 775 K peak carbon species are likely more graphene-like. Results indicate that although carbon deposition nucleation may be initiated at the most active methanation sites,i.e., the Ni step sites, subsequent growth takes place over Ni terracesites. A strongly inhomogeneous carbon growth distribution over the Ni nanoparticle surfaces could also account for our findings. Similarto suggestions regarding catalyst deactivation in Fischer–Tropschsynthesis, a surface CH* coupling mechanism is likely taking place,and our results suggest these polymeric hydrocarbon species become more ordered, aromatic, and eventually graphene-like over time.

U2 - 10.1021/acs.jpcc.7b03754

DO - 10.1021/acs.jpcc.7b03754

M3 - Journal article

VL - 121

SP - 15556

EP - 15564

JO - The Journal of Physical Chemistry Part C

JF - The Journal of Physical Chemistry Part C

SN - 1932-7447

IS - 29

ER -