Highly active and stable MgAl2O4-supported Rh and Ir catalysts for methane steam reforming: A combined experimental and theoretical study

Donghai Mei; Vassiliki Alexandra Glezakou; Vanessa Lebarbier; Libor Kovarik; Haiying Wan; Karl O. Albrecht; Mark Gerber; Roger Rousseau; Robert A. Dagle

doi:10.1016/j.jcat.2014.04.021

Highly active and stable MgAl₂O₄-supported Rh and Ir catalysts for methane steam reforming: A combined experimental and theoretical study

Donghai Mei, Vassiliki Alexandra Glezakou, Vanessa Lebarbier, Libor Kovarik, Haiying Wan, Karl O. Albrecht, Mark Gerber, Roger Rousseau, Robert A. Dagle

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

102 Scopus citations

Abstract

In this work, we present a combined experimental and theoretical investigation of stable MgAl₂O₄-supported Rh and Ir catalysts for the steam methane reforming (SMR) reaction. Catalytic SMR performance for a series of noble metal catalysts supported on MgAl ₂O₄ spinel has been evaluated at 873-1123 K. The turnover rate at 873 K follows the order: Pd > Ir > Pt ∼ Rh > Ru > Ni. However, Rh and Ir are found to have the best combination of activity and stability for SMR in the presence of simulated biomass-derived syngas where highly dispersed ∼2 nm Rh and ∼1 nm Ir clusters are identified on the MgAl₂O₄ spinel support. Scanning Transmission Electron Microscopy (STEM) images show that this excellent dispersion is maintained even under high-temperature conditions (e.g., at 1123 K in the presence of steam), while larger particle sizes of Rh and particularly Ir are observed when supported on Al₂O₃. These observations are further confirmed by ab initio molecular dynamic (AIMD) simulations, which find that ∼1 nm Rh and Ir particles (50-atom cluster) bind strongly to the MgAl ₂O₄ surface via a redox process. The strong metal-support interaction between the spinel support and Rh or Ir helps anchor the metal clusters and reduce the tendency to form larger particle sizes. Density functional theory (DFT) calculations suggest that these supported smaller Rh and Ir particles have a lower work function than larger more bulk-like ones, which enables them to activate both water and methane more effectively than larger particles, yet have a minimal influence on the relative stability of coke precursors. In addition, theoretical mechanistic studies are used to probe the relationship between structure and reactivity. Consistent with the experimental observations, our theoretical modeling results also suggest that the small spinel-supported Ir catalyst is more active than the counterpart Rh catalyst for SMR.

Original language	English
Pages (from-to)	11-23
Number of pages	13
Journal	Journal of Catalysis
Volume	316
DOIs	https://doi.org/10.1016/j.jcat.2014.04.021
State	Published - Jul 2014
Externally published	Yes

Funding

This work was financially supported by the United States Department of Energy (DOE)’s Bioenergy Technologies Office (BETO) and performed at the Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for DOE by Battelle Memorial Institute. Computing time was granted by a user proposal at the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) located at PNNL. Part of the computational time was provided by the National Energy Research Scientific Computing Center (NERSC).

Funders	Funder number
U.S. Department of Energy
Pacific Northwest National Laboratory
Bioenergy Technologies Office

Keywords

Ab initio molecular dynamics
Iridium
Methane steam reforming
Rhodium
Spinel

Access to Document

10.1016/j.jcat.2014.04.021

Cite this

@article{365e559128ee4f83acae1a73038fb13c,

title = "Highly active and stable MgAl2O4-supported Rh and Ir catalysts for methane steam reforming: A combined experimental and theoretical study",

abstract = "In this work, we present a combined experimental and theoretical investigation of stable MgAl2O4-supported Rh and Ir catalysts for the steam methane reforming (SMR) reaction. Catalytic SMR performance for a series of noble metal catalysts supported on MgAl 2O4 spinel has been evaluated at 873-1123 K. The turnover rate at 873 K follows the order: Pd > Ir > Pt ∼ Rh > Ru > Ni. However, Rh and Ir are found to have the best combination of activity and stability for SMR in the presence of simulated biomass-derived syngas where highly dispersed ∼2 nm Rh and ∼1 nm Ir clusters are identified on the MgAl2O4 spinel support. Scanning Transmission Electron Microscopy (STEM) images show that this excellent dispersion is maintained even under high-temperature conditions (e.g., at 1123 K in the presence of steam), while larger particle sizes of Rh and particularly Ir are observed when supported on Al2O3. These observations are further confirmed by ab initio molecular dynamic (AIMD) simulations, which find that ∼1 nm Rh and Ir particles (50-atom cluster) bind strongly to the MgAl 2O4 surface via a redox process. The strong metal-support interaction between the spinel support and Rh or Ir helps anchor the metal clusters and reduce the tendency to form larger particle sizes. Density functional theory (DFT) calculations suggest that these supported smaller Rh and Ir particles have a lower work function than larger more bulk-like ones, which enables them to activate both water and methane more effectively than larger particles, yet have a minimal influence on the relative stability of coke precursors. In addition, theoretical mechanistic studies are used to probe the relationship between structure and reactivity. Consistent with the experimental observations, our theoretical modeling results also suggest that the small spinel-supported Ir catalyst is more active than the counterpart Rh catalyst for SMR.",

keywords = "Ab initio molecular dynamics, Iridium, Methane steam reforming, Rhodium, Spinel",

author = "Donghai Mei and Glezakou, {Vassiliki Alexandra} and Vanessa Lebarbier and Libor Kovarik and Haiying Wan and Albrecht, {Karl O.} and Mark Gerber and Roger Rousseau and Dagle, {Robert A.}",

year = "2014",

month = jul,

doi = "10.1016/j.jcat.2014.04.021",

language = "English",

volume = "316",

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journal = "Journal of Catalysis",

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publisher = "Elsevier",

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TY - JOUR

T1 - Highly active and stable MgAl2O4-supported Rh and Ir catalysts for methane steam reforming

T2 - A combined experimental and theoretical study

AU - Mei, Donghai

AU - Glezakou, Vassiliki Alexandra

AU - Lebarbier, Vanessa

AU - Kovarik, Libor

AU - Wan, Haiying

AU - Albrecht, Karl O.

AU - Gerber, Mark

AU - Rousseau, Roger

AU - Dagle, Robert A.

PY - 2014/7

Y1 - 2014/7

N2 - In this work, we present a combined experimental and theoretical investigation of stable MgAl2O4-supported Rh and Ir catalysts for the steam methane reforming (SMR) reaction. Catalytic SMR performance for a series of noble metal catalysts supported on MgAl 2O4 spinel has been evaluated at 873-1123 K. The turnover rate at 873 K follows the order: Pd > Ir > Pt ∼ Rh > Ru > Ni. However, Rh and Ir are found to have the best combination of activity and stability for SMR in the presence of simulated biomass-derived syngas where highly dispersed ∼2 nm Rh and ∼1 nm Ir clusters are identified on the MgAl2O4 spinel support. Scanning Transmission Electron Microscopy (STEM) images show that this excellent dispersion is maintained even under high-temperature conditions (e.g., at 1123 K in the presence of steam), while larger particle sizes of Rh and particularly Ir are observed when supported on Al2O3. These observations are further confirmed by ab initio molecular dynamic (AIMD) simulations, which find that ∼1 nm Rh and Ir particles (50-atom cluster) bind strongly to the MgAl 2O4 surface via a redox process. The strong metal-support interaction between the spinel support and Rh or Ir helps anchor the metal clusters and reduce the tendency to form larger particle sizes. Density functional theory (DFT) calculations suggest that these supported smaller Rh and Ir particles have a lower work function than larger more bulk-like ones, which enables them to activate both water and methane more effectively than larger particles, yet have a minimal influence on the relative stability of coke precursors. In addition, theoretical mechanistic studies are used to probe the relationship between structure and reactivity. Consistent with the experimental observations, our theoretical modeling results also suggest that the small spinel-supported Ir catalyst is more active than the counterpart Rh catalyst for SMR.

AB - In this work, we present a combined experimental and theoretical investigation of stable MgAl2O4-supported Rh and Ir catalysts for the steam methane reforming (SMR) reaction. Catalytic SMR performance for a series of noble metal catalysts supported on MgAl 2O4 spinel has been evaluated at 873-1123 K. The turnover rate at 873 K follows the order: Pd > Ir > Pt ∼ Rh > Ru > Ni. However, Rh and Ir are found to have the best combination of activity and stability for SMR in the presence of simulated biomass-derived syngas where highly dispersed ∼2 nm Rh and ∼1 nm Ir clusters are identified on the MgAl2O4 spinel support. Scanning Transmission Electron Microscopy (STEM) images show that this excellent dispersion is maintained even under high-temperature conditions (e.g., at 1123 K in the presence of steam), while larger particle sizes of Rh and particularly Ir are observed when supported on Al2O3. These observations are further confirmed by ab initio molecular dynamic (AIMD) simulations, which find that ∼1 nm Rh and Ir particles (50-atom cluster) bind strongly to the MgAl 2O4 surface via a redox process. The strong metal-support interaction between the spinel support and Rh or Ir helps anchor the metal clusters and reduce the tendency to form larger particle sizes. Density functional theory (DFT) calculations suggest that these supported smaller Rh and Ir particles have a lower work function than larger more bulk-like ones, which enables them to activate both water and methane more effectively than larger particles, yet have a minimal influence on the relative stability of coke precursors. In addition, theoretical mechanistic studies are used to probe the relationship between structure and reactivity. Consistent with the experimental observations, our theoretical modeling results also suggest that the small spinel-supported Ir catalyst is more active than the counterpart Rh catalyst for SMR.

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KW - Iridium

KW - Methane steam reforming

KW - Rhodium

KW - Spinel

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DO - 10.1016/j.jcat.2014.04.021

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