On the activation of molecular hydrogen by gold: a theoretical approximation to the nature of potential active sites

Corma, Avelino; Boronat, Mercedes; González, Silvia; Illas, Francesc

doi:10.1039/b708468d

Cited by 160 publications

(187 citation statements)

References 34 publications

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“…Typically, calcination of the gold hydroxide precursor phase results in gold metal nanoparticles with some residual surface oxygen [49]. As a large fraction of gold is already reduced, hydrogen atoms from H 2 dissociation by gold spill over to the ceria support and reduce its surface [50][51][52]. The hydrogen uptake for the cyanideleached Au/CeO 2 (rod) takes place in a much smaller temperature range.…”

Section: Resultsmentioning

confidence: 99%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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The interaction of gold atoms with CeO 2 nanocrystals having rod and cube shapes has been examined by cyanide leaching, TEM, TPR, CO IR and X-ray absorption spectroscopy. After deposition-precipitation and calcination of gold, these surfaces contain gold nanoparticles in the range 2-6 nm. For the ceria nanorods, a substantial amount of gold is present as cations that replace Ce ions in the surface as follows from their first and second coordination shells of oxygen and cerium by EXAFS analysis. These cations are stable against cyanide leaching in contrast to gold nanoparticles. Upon reduction the isolated Au atoms form finely dispersed metal clusters with a high activity in CO oxidation, the WGS reaction and 1,3-butadiene hydrogenation. By analogy with the very low activity of reduced gold nanoparticles on ceria nanocubes exposing the {100} surface plane, it is inferred that the gold nanoparticles on the ceria nanorod surface also have a low activity in such reactions. Although the finely dispersed Au clusters are thermally stable up to quite high temperature in line with earlier findings (Y. Guan and E. J. M. Hensen, Phys Chem Chem Phys 11:9578, 2009), the presence of gold nanoparticles results in their more facile agglomeration, especially in the presence of water (e.g., WGS conditions). For liquid phase alcohol oxidation, metallic gold nanoparticles are the active sites. In the absence of a base, the O-H bond cleavage appears to be rate limiting, while this shifts to C-H bond activation after addition of NaOH. In the latter case, the gold nanoparticles on the surface of ceria nanocubes are much more active than those on the surface of nanorod ceria.

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Section: Resultsmentioning

confidence: 99%

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

et al. 2011

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“…This is extremely important considering that gold, usually does not exhibit ability to chemisorbs H 2 and therefore the hydrogenation capacity is quite low. However, small gold particles behave different, they chemisorb H 2 and they may be active in hydrogenation reactions [32,33]. The use of gold has been pointed out in preliminary researches and due to the well known ability to interacts with NO 2 groups provide the catalysts the unique ability to produce a fast hydrogenation of the nitrocompounds to the corresponding anilines, without accumulation of nitroso and hydroxylamines intermediates and their potential exothermic decomposition.…”

Section: Introductionmentioning

confidence: 99%

“…The accumulation may be diminished by using iron or vanadium-modifies catalysts [27,28]. Recently, the reaction was studied with a using gold as hydrogenation catalyst [29] that gave high selectivity to substituted anilines, but showing lower activity. Nevertheless a catalyst with the same selectivity as gold but with a higher activity would be desired for industrial application [30].…”

Section: Introductionmentioning

confidence: 99%

HYDROGENATION OF NITROBENZENE ON Au/ZrO2 CATALYSTS

Gómez

Torres

Fierro

et al. 2012

J. Chil. Chem. Soc.

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The hydrogenation of nitrobenzene at 298K and pressure of 40 bar of H 2 over zirconia supported Au catalysts has been studied. Three different procedures were used to prepare 1wt% of Au/ZrO 2 catalysts: i) An impregnation method using HAuCl 4 as gold precursor ii)Depositation precipitation of Au nanoparticles generated in the presence of urea and iii) Deposition of Gold nanoparticles generated in presence of cetryltrimethylammonium bromide (CTMABR) as surfactant. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XRD, TEM and XPS techniques. The reactions were carried out in a stainless steel batch reactor using ethanol as solvent. The catalysts exhibits a higher selectivity to aniline, with low accumulation of intermediate products. The kinetic study displayed orders 1 respect to hydrogen pressure and to the substrate concentration (nitrobenzene), and the activation energy was 67.2 KJ/mol.

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“…The hydrogen dissociation on the stepped Au(321) surface was found to be limited by a moderate activation energy barrier. The activation barrier can be visibly reduced on other gold based catalysts such as gold nanoparticles [41] or supported gold nanoparticles, e.g., Au 13 /TiO 2 [42] and Au x /TiC [43,44]. Very recently, the oxidation of alcohols to aldehydes was found to be affected by the surface roughness which was modeled by the consideration of flat and stepped surfaces, rod and Au 38 nanoparticle as gold catalysts models [45].…”

Section: Introductionmentioning

confidence: 99%

Catalytic Reactions on Model Gold Surfaces: Effect of Surface Steps and of Surface Doping

et al. 2011

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Abstract:The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT) based calculations were considered to clarify the role of the low coordinated gold atoms and the role of doping in the catalytic activity of gold. The effect of the surface steps was introduced by comparison of the activation energy barriers and of the adsorption energies on flat gold surfaces such as the Au(111) surface with those on stepped surfaces such as the Au(321) or the Au(110) surfaces. It is concluded that the presence of low coordinated atoms on the latter surfaces increases the adsorption energies of the reactants and decreases the activation energy barriers. Furthermore, the increasing of the adsorption energy of the reaction products can lead to lower overall reaction rates in the presence of low gold coordinated atoms due to desorption limitations. On the other hand, the effect of doping gold surfaces with other transition metal atoms was analyzed using the dissociation reaction of molecular oxygen as a test case. The calculations showed that increasing the silver content in some gold surfaces was related to a considerable increment of the reactivity of bimetallic systems toward the oxygen dissociation. Importantly, that increment in the reactivity was enhanced by the presence of low coordinated atoms in the catalytic surface models considered.

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On the activation of molecular hydrogen by gold: a theoretical approximation to the nature of potential active sites

Cited by 160 publications

References 34 publications

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

Gold Stabilized by Nanostructured Ceria Supports: Nature of the Active Sites and Catalytic Performance

HYDROGENATION OF NITROBENZENE ON Au/ZrO2 CATALYSTS

Catalytic Reactions on Model Gold Surfaces: Effect of Surface Steps and of Surface Doping

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