On the potential role of hydroxyl groups in CO oxidation over Au/Al2O3

Costello, C. K.; Yang, Jason; Wang, Y.; Lin, Jheng-Hua; Marks, Laurence D.; Kung, Mayfair C.; Kung, Harold H.

doi:10.1016/s0926-860x(02)00533-1

Cited by 254 publications

(139 citation statements)

References 30 publications

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“…Costello et al [18] agree with the proposal of a significant role for hydroxyls in CO oxidation. They demonstrated a significant kinetic isotope effect in the oxidation of CO in the presence of H 2 but not with water, attributing the difference to the different kinetic isotope effects expected for the regeneration of Au/Al 2 O 3 sites by hydrogen and water.…”

Section: The Influence Of Water On Carbon Monoxide Oxidation Over Golsupporting

confidence: 55%

“…Adapted with permission from Costello's model from Ref. [18] hydroxyl groups on the support is to stabilise water near the Au/TiO 2 interface and it is proton transfer reactions involving water that are crucial with a *OOH intermediate forming on the gold surface from O 2 that reacts readily with CO to form *COOH and O*. Decomposition of the *COOH intermediate is again facilitated by the presence of water.…”

Section: The Influence Of Water On Carbon Monoxide Oxidation Over Golmentioning

confidence: 99%

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On the Role of Water in Heterogeneous Catalysis: A Tribute to Professor M. Wyn Roberts

Davies

2016

Top Catal

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From the earliest studies of heterogeneous catalysis, it was apparent that water plays a more important role in many systems than simply acting as a solvent. Its wide ranging effects have attracted increasing attention in recent years and was the topic of Prof. M.W. Roberts' final paper. The present review explores some of the latest work on water in reactions ranging from CO oxidation to Fischer-Tropsch catalysis, the different mechanisms proposed for its role are discussed and compared.

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Section: The Influence Of Water On Carbon Monoxide Oxidation Over Golsupporting

confidence: 55%

Section: The Influence Of Water On Carbon Monoxide Oxidation Over Golmentioning

confidence: 99%

On the Role of Water in Heterogeneous Catalysis: A Tribute to Professor M. Wyn Roberts

Davies

2016

Top Catal

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“…Bearing in mind the reductive pre-treatment of the catalyst and bare ␥-Al 2 O 3 with H 2 , the reaction of CO with surface hydroxyl, as in a step in water gas-shift reaction might seem much more likely. Costello et al (8) studying the potential role of hydroxyl groups in CO oxidation over Au/Al 2 O 3 suggested a model of the active site involving an ensemble of metallic Au atoms and Au + -OH -. While there is spectroscopic evidence of the presence of Au cations in an active catalyst, although their role in the CO oxidation reaction is not accepted unequivocally (10), there is only inferential evidence of the presence and particularly the participation, of hydroxyl groups in the reaction (8).…”

Section: Figurementioning

confidence: 99%

“…Costello et al (8) studying the potential role of hydroxyl groups in CO oxidation over Au/Al 2 O 3 suggested a model of the active site involving an ensemble of metallic Au atoms and Au + -OH -. While there is spectroscopic evidence of the presence of Au cations in an active catalyst, although their role in the CO oxidation reaction is not accepted unequivocally (10), there is only inferential evidence of the presence and particularly the participation, of hydroxyl groups in the reaction (8). While the decomposition of CO at high temperatures, over bare ␥-Al 2 O 3 is probably related to Al-hydroxyls, the low temperature activity of Au/␥-Al 2 O 3 for CO decomposition much more likely indicates that Au-hydroxyls are involved in the formation of CO 2 .…”

Section: Figurementioning

confidence: 99%

“…Among the various supported Au catalysts, Au/Al 2 O 3 is perhaps one that has shown the widest variation for CO oxidation, ranging from being very inactive to practically as active as Au/TiO 2 (8). Compared to Au/␥-Al 2 O 3 , multicomponent gold-based catalysts also supported on ␥-Al 2 O 3 and combined with common metal oxides, such as: MnO x , MgO, FeO x (9,10) as well as gold catalysts supported on other materials such as Au/TiO 2 (11) and Au/FeO x (11,12) have been found to exhibit even more promising commercial performance for the SCO reaction.…”

Section: Introductionmentioning

confidence: 99%

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On the mechanism of selective CO oxidation on nanosized Auγ-Al2O3 catalysts

et al. 2006

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Nanometer-sized gold particles on oxide supports are efficient catalysts for the selective catalytic oxidation (SCO) of carbon monoxide under conditions compatible with the operation of PEM fuel cells. Nanosized Au/␥-Al 2 O 3 catalysts are able to oxidize CO between 20 and 70°C in an atmosphere of hydrogen combining high CO conversion and satisfactory selectivity to CO 2 (1). It is generally agreed that the catalytic activity of gold depends on the size of the gold particles, but the nature of support material, the preparation method, the activation procedure have also been suggested to play a key role (2). Sites at the gold support interface have also been claimed to be responsible for the activity in CO oxidation (3). Strain in the Au particles due to the mismatch of the lattices at the interface with the support (4) and the effect of low-coordinated sites and roughness (4) have also been suggested as important factors for high activity. The most important effect, concerning the catalytic activity of gold nanoparticles for low temperature oxidation of CO is related to the availability of many low-coordinated gold atoms on the small particles (5). Effects related to the interaction with the support may also contribute, but to a considerably smaller extent (5).CO oxidation over group VIII noble metals is the most studied catalytic reaction. However, selective oxidation of CO in hydrogen-rich conditions is not as well studied (6,7). CO (reactant) and CO 2 (product) sorption processes are fundamental elementary steps for SCO and moreover, the effect of hydrogen on their sorption over supported Au catalysts remains a subject of significant interest.Among the various supported Au catalysts, Au/Al 2 O 3 is perhaps one that has shown the widest variation for CO oxidation, ranging from being very inactive to practically as active as Au/TiO 2 (8). Compared to Au/␥-Al 2 O 3 , multicomponent gold-based catalysts also supported on ␥-Al 2 O 3 and combined with common metal oxides, such as: MnO x , MgO, FeO x (9,10) as well as gold catalysts supported on other materials such as Au/TiO 2 (11) and Au/FeO x (11,12) have been found to exhibit even more promising commercial performance for the SCO reaction. However, based on its simplicity, a well-studied Au/␥-Al 2 O 3 catalyst (1,9) has been utilized in the present work as model system, in order to gain fundamental information on the catalytic behaviour of gold nanoparticles and identify the active sites on Au/␥-Al 2 O 3 .In this paper, new findings which offer further information concerning the mechanism of CO preferential oxidation over nanosized Au are presented. The first finding concerns CO 2 formation in the absence of oxygen and hydrogen both in bare ␥-Al 2 O 3 as well as in Au/␥-Al 2 O 3 (called as CO decomposition). At high temperatures (>200 °C) in excess of H 2 , over the Au/␥-Al 2 O 3 catalyst, reversed water gas shift (RWGS) reaction results in CO 2 consumption towards CO and H 2 O formation. Finally, the kinetic measurements of the present work indicate that hydrog...

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Gold Nanoparticles: Recent Advances in CO Oxidation

Louis

2007

Nanoparticles and Catalysis

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IntroductionThe oxidation of carbon monoxide at around room temperature is the most famous reaction known for gold catalysts. Haruta ' s group discovered in 1987 [1, 2] that gold is a unique catalyst for this reaction when gold metal particles are smaller than 5 nm and supported on oxides. Since then, extensive and intensive fundamental works have been published, and expanding new applications, from air purifi cation (gas masks, gas sensors, indoor air quality control) to hydrogen purifi cation for fuel cells (PROX, preferential selective oxidation of CO in the presence of H 2 ) have been developed.Gold is indeed active in carbon monoxide oxidation at a much lower temperature ( ≤ RT) than any platinum group metal [3] ( Fig. 15.1 ). The difference in reactivity can be due to the fact that Pt, Pd and Rh easily dissociate molecular oxygen at low temperature and bind strongly both atomic oxygen and CO. Tightly bound adsorbates have to overcome sizeable barriers to react, making the reaction rates signifi cant only at rather high temperatures [4] . On the contrary, on gold the reactants are loosely bound, but a higher binding energy of CO on gold nanoparticles than on bulk gold may provide suffi cient concentrations of CO on the surface for the reaction of oxidation to occur with negligible energy barriers. The main problem with this apparently simple reaction is that if CO is known to adsorb on low coordinated surface gold sites, the adsorption and activation of oxygen on gold particles is more puzzling (Section 15.4.3 ). The CO oxidation mechanism is not yet elucidated in spite of the huge number of papers published, and four main mechanisms have been suggested.High activity in CO oxidation when gold particles are smaller than 5 nm, and supported on reducible oxides, such as iron oxide or titania, led Haruta et al. [3, 5 -8] to propose the fi rst mechanism of CO oxidation (Fig. 15.2 ): the reaction takes place at the interface between the gold metal particle and the oxide support, i.e., between CO adsorbed on the gold particles and O 2 activated by the oxide support. Later, based on the assumption that metal cations could be located at the metalsupport interface, Bond and Thompson [9] proposed a mechanism rather similar, 475Nanoparticles and Catalysis. Edited by Didier Astruc

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On the potential role of hydroxyl groups in CO oxidation over Au/Al2O3

Cited by 254 publications

References 30 publications

On the Role of Water in Heterogeneous Catalysis: A Tribute to Professor M. Wyn Roberts

On the Role of Water in Heterogeneous Catalysis: A Tribute to Professor M. Wyn Roberts

On the mechanism of selective CO oxidation on nanosized Auγ-Al2O3 catalysts

Gold Nanoparticles: Recent Advances in CO Oxidation

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