CO oxidation over ceria supported Au22 nanoclusters: Shape effect of the support

Zili Wu; David R. Mullins; Lawrence F. Allard; Qianfan Zhang; Laisheng Wang

doi:10.1016/j.cclet.2018.01.038

CO oxidation over ceria supported Au₂₂ nanoclusters: Shape effect of the support

Zili Wu, David R. Mullins, Lawrence F. Allard, Qianfan Zhang, Laisheng Wang

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

44 Scopus citations

Abstract

Gold (Au) nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au₂₂(L⁸)₆ (L = 1,8-bis(diphenylphosphino) octane) nanoclusters were supported on CeO₂ rods or cubes, then pretreated at different temperatures (up to 673 K), allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO₂ rods are much better supports than cubes for Au₂₂ nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO₂ support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO₂ rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites (denoted by Au^δ+, 0 < δ < 1) is lower than that on CeO₂ cubes. The in situ extended X-ray absorption spectroscopy (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the Au nanoclusters bound more strongly to the CeO₂ rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO₂ is the determining factor for CO oxidation over Au₂₂/CeO₂. CeO₂ rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.

Original language	English
Pages (from-to)	795-799
Number of pages	5
Journal	Chinese Chemical Letters
Volume	29
Issue number	6
DOIs	https://doi.org/10.1016/j.cclet.2018.01.038
State	Published - Jun 2018

Funding

The work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. Part of the work including the IR study was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy, Sciences under Contract No. DE-AC02-76SF00515. We acknowledge the facilities support at the beamline BL 2-2 provided by the Synchrotron Catalysis Consortium U.S. DOE (No. De-SC0012335).

Funders	Funder number
Office of Basic Energy, Sciences	DE-AC02-76SF00515
U.S. Department of Energy
Office of Science
Basic Energy Sciences
Chemical Sciences, Geosciences, and Biosciences Division

Keywords

CO oxidation
Ceria
Gold nanoclusters
Ligands
Support shape

Access to Document

10.1016/j.cclet.2018.01.038

Cite this

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title = "CO oxidation over ceria supported Au22 nanoclusters: Shape effect of the support",

abstract = "Gold (Au) nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au22(L8)6 (L = 1,8-bis(diphenylphosphino) octane) nanoclusters were supported on CeO2 rods or cubes, then pretreated at different temperatures (up to 673 K), allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO2 rods are much better supports than cubes for Au22 nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO2 support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO2 rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites (denoted by Auδ+, 0 < δ < 1) is lower than that on CeO2 cubes. The in situ extended X-ray absorption spectroscopy (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the Au nanoclusters bound more strongly to the CeO2 rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO2 is the determining factor for CO oxidation over Au22/CeO2. CeO2 rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.",

keywords = "CO oxidation, Ceria, Gold nanoclusters, Ligands, Support shape",

author = "Zili Wu and Mullins, {David R.} and Allard, {Lawrence F.} and Qianfan Zhang and Laisheng Wang",

note = "Publisher Copyright: {\textcopyright} 2018 The Author",

year = "2018",

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doi = "10.1016/j.cclet.2018.01.038",

language = "English",

volume = "29",

pages = "795--799",

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TY - JOUR

T1 - CO oxidation over ceria supported Au22 nanoclusters

T2 - Shape effect of the support

AU - Wu, Zili

AU - Mullins, David R.

AU - Allard, Lawrence F.

AU - Zhang, Qianfan

AU - Wang, Laisheng

PY - 2018/6

Y1 - 2018/6

N2 - Gold (Au) nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au22(L8)6 (L = 1,8-bis(diphenylphosphino) octane) nanoclusters were supported on CeO2 rods or cubes, then pretreated at different temperatures (up to 673 K), allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO2 rods are much better supports than cubes for Au22 nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO2 support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO2 rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites (denoted by Auδ+, 0 < δ < 1) is lower than that on CeO2 cubes. The in situ extended X-ray absorption spectroscopy (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the Au nanoclusters bound more strongly to the CeO2 rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO2 is the determining factor for CO oxidation over Au22/CeO2. CeO2 rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.

AB - Gold (Au) nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au22(L8)6 (L = 1,8-bis(diphenylphosphino) octane) nanoclusters were supported on CeO2 rods or cubes, then pretreated at different temperatures (up to 673 K), allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO2 rods are much better supports than cubes for Au22 nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO2 support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO2 rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites (denoted by Auδ+, 0 < δ < 1) is lower than that on CeO2 cubes. The in situ extended X-ray absorption spectroscopy (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the Au nanoclusters bound more strongly to the CeO2 rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO2 is the determining factor for CO oxidation over Au22/CeO2. CeO2 rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.

KW - CO oxidation

KW - Ceria

KW - Gold nanoclusters

KW - Ligands

KW - Support shape

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