CO oxidation on phosphate-supported Au catalysts: Effect of support reducibility on surface reactions

Meijun Li; Zili Wu; S. H. Overbury

doi:10.1016/j.jcat.2010.11.019

CO oxidation on phosphate-supported Au catalysts: Effect of support reducibility on surface reactions

Meijun Li, Zili Wu, S. H. Overbury

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Abstract

Previous work has shown that Au supported on FePO₄ can be stable and active for CO oxidation and that oxygen from the FePO₄ can participate in the CO oxidation. In this paper, we have used gas transient DRIFTS-QMS, Raman, temperature-programmed reduction and CO oxidation activity measurements to compare adsorption and oxidation of CO on two comparably loaded Au catalysts supported on both a reducible phosphate support, FePO₄, and a non-reducible support, LaPO₄. H₂-TPR confirms that the Au/FePO₄ catalyst is highly reducible and that the reduction is strongly promoted by the Au, while neither LaPO₄ nor Au/LaPO ₄ are reducible up to 500 °C. The nature of Au species was determined by CO adsorption. For Au/FePO₄, cationic Au is present after oxidative treatment, and metallic Au dominates after reductive treatment. The majority of the cationic Au observed on the FePO₄ support undergoes in situ reduction to metallic Au during rt CO adsorption. For Au/LaPO₄, no cationic Au is observed, but metallic Au is present after both oxidative and reductive treatment. In addition, metallic Au is accompanied by anionic Au, not seen on Au/FePO₄, which accumulates during CO exposure, even after an oxidative pretreatment. Unexpectedly, CO interacts rapidly with Au/LaPO₄ to evolve CO₂ and form both adsorbed CO₂ and "carbonate-like" species, even though the LaPO₄ is non-reducible and Raman fails to find evidence for loss of structural oxygen. H₂ coevolves with CO₂ during CO-TPR of Au/LaPO₄ (but not for Au/FePO₄) leading to the conclusion that surface hydroxyl is the source of oxygen during CO exposure to Au/LaPO₄. Anionic Au is associated with the vacancies remaining after reaction of hydroxyl with CO.

Original language	English
Pages (from-to)	133-142
Number of pages	10
Journal	Journal of Catalysis
Volume	278
Issue number	1
DOIs	https://doi.org/10.1016/j.jcat.2010.11.019
State	Published - Feb 14 2011

Funding

This research was sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, US Department of Energy. A portion of this research was performed using facilities at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. Meijun Li was sponsored by an appointment to the Oak Ridge National Laboratory Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute for Science and Education and Oak Ridge National Laboratory.

Funders	Funder number
Oak Ridge National Laboratory
Scientific User Facilities Division
U.S. Department of Energy
Basic Energy Sciences
Oak Ridge National Laboratory
Oak Ridge Institute for Science and Education
Chemical Sciences, Geosciences, and Biosciences Division

Keywords

Au catalyst
CO adsorption
Catalytic CO oxidation
FTIR
FePO
LaPO
Mechanism
Raman spectroscopy

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10.1016/j.jcat.2010.11.019

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title = "CO oxidation on phosphate-supported Au catalysts: Effect of support reducibility on surface reactions",

abstract = "Previous work has shown that Au supported on FePO4 can be stable and active for CO oxidation and that oxygen from the FePO4 can participate in the CO oxidation. In this paper, we have used gas transient DRIFTS-QMS, Raman, temperature-programmed reduction and CO oxidation activity measurements to compare adsorption and oxidation of CO on two comparably loaded Au catalysts supported on both a reducible phosphate support, FePO4, and a non-reducible support, LaPO4. H2-TPR confirms that the Au/FePO4 catalyst is highly reducible and that the reduction is strongly promoted by the Au, while neither LaPO4 nor Au/LaPO 4 are reducible up to 500 °C. The nature of Au species was determined by CO adsorption. For Au/FePO4, cationic Au is present after oxidative treatment, and metallic Au dominates after reductive treatment. The majority of the cationic Au observed on the FePO4 support undergoes in situ reduction to metallic Au during rt CO adsorption. For Au/LaPO4, no cationic Au is observed, but metallic Au is present after both oxidative and reductive treatment. In addition, metallic Au is accompanied by anionic Au, not seen on Au/FePO4, which accumulates during CO exposure, even after an oxidative pretreatment. Unexpectedly, CO interacts rapidly with Au/LaPO4 to evolve CO2 and form both adsorbed CO2 and {"}carbonate-like{"} species, even though the LaPO4 is non-reducible and Raman fails to find evidence for loss of structural oxygen. H2 coevolves with CO2 during CO-TPR of Au/LaPO4 (but not for Au/FePO4) leading to the conclusion that surface hydroxyl is the source of oxygen during CO exposure to Au/LaPO4. Anionic Au is associated with the vacancies remaining after reaction of hydroxyl with CO.",

keywords = "Au catalyst, CO adsorption, Catalytic CO oxidation, FTIR, FePO, LaPO, Mechanism, Raman spectroscopy",

author = "Meijun Li and Zili Wu and Overbury, {S. H.}",

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T2 - Effect of support reducibility on surface reactions

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AU - Wu, Zili

AU - Overbury, S. H.

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N2 - Previous work has shown that Au supported on FePO4 can be stable and active for CO oxidation and that oxygen from the FePO4 can participate in the CO oxidation. In this paper, we have used gas transient DRIFTS-QMS, Raman, temperature-programmed reduction and CO oxidation activity measurements to compare adsorption and oxidation of CO on two comparably loaded Au catalysts supported on both a reducible phosphate support, FePO4, and a non-reducible support, LaPO4. H2-TPR confirms that the Au/FePO4 catalyst is highly reducible and that the reduction is strongly promoted by the Au, while neither LaPO4 nor Au/LaPO 4 are reducible up to 500 °C. The nature of Au species was determined by CO adsorption. For Au/FePO4, cationic Au is present after oxidative treatment, and metallic Au dominates after reductive treatment. The majority of the cationic Au observed on the FePO4 support undergoes in situ reduction to metallic Au during rt CO adsorption. For Au/LaPO4, no cationic Au is observed, but metallic Au is present after both oxidative and reductive treatment. In addition, metallic Au is accompanied by anionic Au, not seen on Au/FePO4, which accumulates during CO exposure, even after an oxidative pretreatment. Unexpectedly, CO interacts rapidly with Au/LaPO4 to evolve CO2 and form both adsorbed CO2 and "carbonate-like" species, even though the LaPO4 is non-reducible and Raman fails to find evidence for loss of structural oxygen. H2 coevolves with CO2 during CO-TPR of Au/LaPO4 (but not for Au/FePO4) leading to the conclusion that surface hydroxyl is the source of oxygen during CO exposure to Au/LaPO4. Anionic Au is associated with the vacancies remaining after reaction of hydroxyl with CO.

AB - Previous work has shown that Au supported on FePO4 can be stable and active for CO oxidation and that oxygen from the FePO4 can participate in the CO oxidation. In this paper, we have used gas transient DRIFTS-QMS, Raman, temperature-programmed reduction and CO oxidation activity measurements to compare adsorption and oxidation of CO on two comparably loaded Au catalysts supported on both a reducible phosphate support, FePO4, and a non-reducible support, LaPO4. H2-TPR confirms that the Au/FePO4 catalyst is highly reducible and that the reduction is strongly promoted by the Au, while neither LaPO4 nor Au/LaPO 4 are reducible up to 500 °C. The nature of Au species was determined by CO adsorption. For Au/FePO4, cationic Au is present after oxidative treatment, and metallic Au dominates after reductive treatment. The majority of the cationic Au observed on the FePO4 support undergoes in situ reduction to metallic Au during rt CO adsorption. For Au/LaPO4, no cationic Au is observed, but metallic Au is present after both oxidative and reductive treatment. In addition, metallic Au is accompanied by anionic Au, not seen on Au/FePO4, which accumulates during CO exposure, even after an oxidative pretreatment. Unexpectedly, CO interacts rapidly with Au/LaPO4 to evolve CO2 and form both adsorbed CO2 and "carbonate-like" species, even though the LaPO4 is non-reducible and Raman fails to find evidence for loss of structural oxygen. H2 coevolves with CO2 during CO-TPR of Au/LaPO4 (but not for Au/FePO4) leading to the conclusion that surface hydroxyl is the source of oxygen during CO exposure to Au/LaPO4. Anionic Au is associated with the vacancies remaining after reaction of hydroxyl with CO.

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KW - CO adsorption

KW - Catalytic CO oxidation

KW - FTIR

KW - FePO

KW - LaPO

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SN - 0021-9517

VL - 278

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EP - 142

JO - Journal of Catalysis

JF - Journal of Catalysis

IS - 1

ER -

CO oxidation on phosphate-supported Au catalysts: Effect of support reducibility on surface reactions

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Keywords

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