Stabilization of cationic gold species on Au/CeO2 catalysts under working conditions

doi:10.1016/j.apcata.2006.03.004

Applied Catalysis A: General

Volume 307, Issue 1, 12 June 2006, Pages 42-45

https://doi.org/10.1016/j.apcata.2006.03.004 Get rights and content

Abstract

Infrared spectroscopy of CO adsorption at low temperature has shown the presence of oxidized gold species (Au⁺ and Au³⁺) on nanocrystalline Au/CeO₂ catalyst. This species are quite stable even under reduction conditions like the CO oxidation reaction. The concentration of this species decrease by increasing the pre-treatment temperature of the Au/CeO₂ catalyst which is in accordance with a decrease in the catalytic activity of the sample. In accordance oxidized gold species are involved in the catalytic activity of Au/CeO₂ catalyst for CO oxidation although the participation of metallic sites cannot be excluded.

Introduction

In the last years gold catalysts supported on metal oxides have been reported to be highly active for several reactions including low temperature CO oxidation [1], [2], [3]. It has been shown how the catalytic activity of these catalysts is strongly influenced by gold particle size, synthesis method, pre-treatment conditions and the nature of the support [3]. The supports have been differentiated between those able to provide oxygen (reducible) and those not able to do so because of their inability to adsorb oxygen [4]. In the case of reducible oxides supports, oxygen is thought to adsorb on the support and successively interact with the CO adsorbed on the gold particles [5], for this reason the activity is extremely dependent on the type of structure of the metal-support interface [4]. Thus, it has been presented that gold clusters supported on nanocrystalline and mesostructured nanocrystalline CeO₂ or Y₂O₃ is much more active for oxidations [6], [7], [8] as well as for carbon–carbon bond formation [9] than gold clusters on conventional CeO₂ or Y₂O₃ supports. More specifically, supported on nanocrystalline CeO₂ presents high activity for CO oxidation [6] and the support supplies reactive oxygen (in the form of superoxide and peroxide species) to the active gold sites [10]. The interface between metallic gold particles and the support appears to be critical for high CO oxidation activity [10], [11], and time-resolved XANES spectra have shown the presence of cationic gold clusters in the Au/CeO₂ catalyst, which were stable during CO oxidation [12]. The presence of Au⁺ and Au³⁺ species has also been evidenced by XPS analysis [10]. Several authors suggested the crucial role of oxidized gold species [13], [14], or even the cooperative role of metallic and oxidized gold species [15], [16] for the low temperature CO oxidation, while others propose only metallic gold as the active species [17].

In the work reported here FTIR spectroscopy has been employed, as a surface sensitive technique, in order to determine the nature of gold species present on Au/CeO₂ catalysts under reaction conditions. Due to the rapid reduction at room temperature of ionic gold in contact with CO, even in the presence of oxygen, the characterisation of the catalyst was carried out by freezing down the reaction in liquid N₂ and analyzing the nature of gold species using CO as a probe molecule.

Section snippets

Experimental

The catalysts were prepared starting from nanocrystalline CeO₂ and HAuCl₄ according to a procedure previously described [6]. As-prepared samples and H₂-reduced samples at 373 and 573 K have been studied.

The catalytic tests were performed with powdered catalysts, diluted with SiC, in a 9 mm i.d. quartz reactor, at different contact times $(W / F = g_{cat} h mo l_{CO}^{- 1})$ , using 2% CO–1% O₂–He as gas reaction mixture (50 ml/min). The products were analyzed by gas chromatography using Porapack and Molecular Sieves

Results and discussion

The catalytic activity of gold supported on nanocrystalline CeO₂ strongly depends on the catalyst pre-treatment (Fig. 1). The highest catalytic activity was obtained with the as-prepared catalyst while reduction in H₂ strongly reduces the activity. Sintering of gold metal particles due to high temperature pre-treatment has been reported to decrease drastically the activity of gold supported catalysts [3]. However in this case, although the presence of metallic gold particles has been seen in

Acknowledgements

The authors thank European Union network AURICAT (HPRN-CT-2002-00174) and CICYT (MAT2003-07945-C02-01) for financial support.

References (28)

M. Haruta et al.
J. Catal.
(1989)
M.M. Schubert et al.
J. Catal.
(2001)
S. Carrettin et al.
Appl. Catal.
(2005)
M.A. Centeno et al.
Appl. Catal. A: Gen.
(2002)
J.D. Grunwaldt et al.
J. Catal.
(1999)
T. Tabakova et al.
Appl. Catal. A: Gen.
(2003)
F. Boccuzzi et al.
Surf. Sci.
(2000)
F. Boccuzzi et al.
Surf. Sci.
(2002)
H. Liu et al.
J. Catal.
(1999)
M.I. Zaki et al.
J. Catal.
(1989)

P. Concepción et al.

J. Catal.

(1999)

G.J. Hutchings

Gold Bull.

(1996)

G.C. Bond et al.

Catal. Rev. Sci. Eng.

(1999)

J.C. Frost

Nature

(1988)

Cited by (90)

Nano-Gold Boosted Environmental Catalysis
2020, Advanced Nanomaterials for Pollutant Sensing and Environmental Catalysis
In this chapter, a comprehensive introduction to nanosized gold-based catalysts and their applications in environmental catalysis will be given. Gold-based catalysts can be divided into two kinds, namely (1) catalysts with the activity raising from effective charge transfer, the quantum size effect, and the nanostructured gold itself, and (2) surface plasmon resonance–enhanced photocatalysts. The environmental applications of these two kinds of gold-based catalysts, including catalytic oxidation of CO, catalytic decomposition of volatile organic compounds, removal of nitrogen oxides, and ozone decomposition have been introduced in the working principle, and research progress through the classic example.
Thermally induced sintering and redispersion of Au nanoparticles supported on Ce<inf>1-x</inf>Eu<inf>x</inf>O<inf>2</inf> nanocubes and their influence on catalytic CO oxidation
2019, Catalysis Communications
The effect of Eu doping of ceria nanocubes on the morphology, oxidation state of deposited Au particles and their activity in CO oxidation was studied. The decisive role of doping of ceria support with Eu in the sintering of deposited Au nanoparticles has been established and discussed for the first time. The redispersion of gold nanoparticles is responsible for the formation of small, ca. ~1 nm Au nanoclusters, and as a consequence the increase of the number of active sites participating in CO-oxidation reaction.
Nano-Gold Boosted Environmental Catalysis
2019, Advanced Nanomaterials for Pollutant Sensing and Environmental Catalysis
In this chapter, a comprehensive introduction to nanosized gold-based catalysts and their applications in environmental catalysis will be given. Gold-based catalysts can be divided into two kinds, namely (1) catalysts with the activity raising from effective charge transfer, the quantum size effect, and the nanostructured gold itself, and (2) surface plasmon resonance–enhanced photocatalysts. The environmental applications of these two kinds of gold-based catalysts, including catalytic oxidation of CO, catalytic decomposition of volatile organic compounds, removal of nitrogen oxides, and ozone decomposition have been introduced in the working principle, and research progress through the classic example.
Gold supported on ceria nanotubes for CO oxidation
2017, Applied Surface Science
CeO₂ is a typical of fluorite structure, semiconductor material, has high oxygen storage capability as well as unique redox property, which is widely used as catalysts supports in catalysis. Ceria nanotubes and nanocubes are prepared via hydrothermal method in the present work, and Au/CeO₂ catalysts are prepared using deposition-precipitation technique with HAuCl₄ as gold precursor. The prepared samples were used as catalysts for the CO oxidation reaction using a fix-bed reactor at 50–130 °C and characterized by XRD, BET, SEM, TEM, XPS, TPR and ICP. It is found that CeO₂-NT and CeO₂-NC expose different surface planes. The XPS and H₂-TPR results illustrates that the {110} surface exposed by CeO₂-NT has stronger interaction with gold particles, which benefits the electron and oxygen transfer between Au and ceria. All these characters of the Au/CeO₂-NT(3%) result in the better activity and stability than the Au/CeO₂-NC(3%).
On the activity of supported Au catalysts in the liquid phase hydrogenation of CO<inf>2</inf> to formates
2016, Journal of Catalysis
The performance of a range of nanoparticulate gold catalysts in the hydrogenation of carbon dioxide to formates was investigated and a superior performance of Au/Al₂O₃ was revealed. The comparative studies with unsupported gold nanoparticles pointed to the crucial role of the metal–support interaction for the CO₂ hydrogenation activity. Cyanide leaching tests complemented by XPS and STEM studies point to the importance of metallic Au⁰ species for the catalytic activity. The Au/Al₂O₃ catalyst shows stable activity that allows reaching equilibrium formate yields in a broad temperature range. A kinetic study revealed that a near-zero apparent activation barrier for the hydrogenation reaction is an intrinsic property of the catalytic system. The reaction mechanism is proposed on the basis of the obtained reactivity and characterization data.
A promoting effect of dilution of Pd sites due to gold surface segregation under reaction conditions on supported Pd-Au catalysts for the selective hydrogenation of 1,5-cyclooctadiene
2016, Catalysis Today
Restructuration of AuPd/CeO₂ catalysts is observed during 1,5-cyclooctadiene hydrogenation, with gold surface segregation in which gold acts as a diluent of Pd surface sites. The composition of the catalyst influences the catalytic behavior, and an optimum is observed at a Pd/Au molar ratio of 0.13, as determined by X-EDS STEM. Pd–Au/CeO₂ shows higher hydrogenation rates (11.2 × 10⁻⁵ mol/g s) versus the unpromoted Pd/CeO₂ catalysts (1.7 × 10⁻⁵ mol/g s), and the Pd/TiO₂ (7.5 × 10⁻⁵ mol/g s) catalysts used as conventional hydrogenation catalysts. Since the active sites are generated under reaction conditions, characterization of the catalysts after quenching the reaction at specific reaction times was required.

View all citing articles on Scopus

View full text

Stabilization of cationic gold species on Au/CeO2 catalysts under working conditions

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Acknowledgements

J. Catal.

J. Catal.

Appl. Catal.

Appl. Catal. A: Gen.

J. Catal.

Appl. Catal. A: Gen.

Surf. Sci.

Surf. Sci.

J. Catal.

J. Catal.

J. Catal.

Gold Bull.

Catal. Rev. Sci. Eng.

Nature

Stabilization of cationic gold species on Au/CeO₂ catalysts under working conditions