Exceptional oxidation activity with size-controlled supported gold clusters of low atomicity

Abstract

Nature Publishing GroupCorma Canós, A.; Concepción Heydorn, P.; Boronat Zaragoza, M.; Sabater Picot, MJ.; Navas Escrig, J.; Yacaman, MJ.; Larios, E.... (2013). Exceptional oxidation activity with sizecontrolled supported gold clusters of low atomicity. Nature Chemistry. 5 (9) SummaryThe catalyticic activity of gold depends on particle size, with reactivity increasing as particle diameter decreases. Investigation of the trends in the subnanometer regime, where gold exists as small clusters of a few atoms, is now starting thanks to recent advances in synthesis and characterization techniques. An easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O 2 are described. Single gold atoms are not active and they aggregate under reaction conditions into gold clusters of low atomicity, which show a catalytic activity comparable to that sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero.Theoretical calculations show that gold clusters are able to simultaneously activate thiophenol and O 2 , while larger nanoparticles become passivated by strongly adsorbed thiolates. The combination of an optimum for reactants activation and product desorption makes gold clusters excellent catalysts. Main TextGold has attracted wide interest as catalyst in the last years due to its unexpected activity and, specially, to its high selectivity in organic reactions. [1][2][3] The catalytic properties of gold depend on several factors that in some cases are intimately related:gold particle size and morphology, metal-oxide support interaction, oxidation state of the active sites, etc. 4-8 The influence of particle size has been extensively investigated, and a volcano type curve with a maximum in activity at an optimum diameter has been reported for CO oxidation, 7 alkane oxidation, 9 or propene epoxidation with O 2 and H 2 , 10 while in other cases an exponential increase in activity with decreasing particle size has been observed. 5,11,12 However, the trends in catalytic activity when the particle diameter While it appears that in order to control reactivity, the atomicity control of the gold clusters is crucial, the synthesis of size-selected metal clusters and their deposition over a solid support is a challenging task. 26 The wet-chemistry methods for preparing supported metal clusters involve the anchoring of well defined precursors to an adequate support, 27,28 followed by removal of the ligands by post-synthesis treatments, trying to prevent cluster agglomeration during these steps. 9,[29][30][31]32 Soft landing of monodisperse metal clusters grown in the gas phase and with precise size selection by mass spectrometry is a more straightforward method, but it requires sophisticated equipment, and the scaling up of the process is a major drawback. 20,23,33 In The chemical nature of these isolated atoms has been investigated by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spe...

Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina

“…In previous work with Au catalysts, the authors had to leach out the metallic component before performing catalytic tests 2,20 . Even if the initial catalyst is in the form of atomically dispersed species, the catalyst can evolve during reaction measurement, as shown by Guan et al 21 and, more recently, by Corma et al 22 These authors suggest that atomically dispersed species can serve as precursors for the formation of very small clusters of the metal. Hence, it is necessary to use in situ spectroscopy to confirm the identity of the species responsible for catalytic reactivity.…”

Nanocluster structure deduced from AC-STEM images coupled to theoretical modelling

“…Publications describing structural determination of nanoclusters and other nanosized systems using AC-STEM have appeared in the past decade, see for example Refs. [7][8][9][10][11][12].…”

Metallic Clusters: Theoretical Background, Properties and Synthesis in Microemulsions

“…The exceptional oxidation activity for the oxidation of thiophenol by small gold clusters (between five and 10 atoms) has been reported recently [24]. This extraordinary activity compares to that of sulfhydryl oxidase enzymes and is not found either for gold nanoparticles (or bulk) or for single gold atoms or clusters with less than five atoms.…”

“…In Figure 6, a compilation of different reported PL data [22][23][24][25][26] has been plotted together.…”