Nanocrystalline CeO₂ Increases the Activity of Au for CO Oxidation by Two Orders of Magnitude

Abstract

More than twenty years ago it was shown that gold, despite its limited adsorption properties, catalyzes reactions such as CO oxidation, [1] alkene hydrogenation, [2] and ethylene hydrochlorination.[3] However, strong interest in gold for catalysis emerged only recently owing to the seminal work of Haruta et al. [4] These authors showed that when gold is deposited on a metal-oxide support by a coprecipitation method, the metal exhibits high catalytic activity for CO oxidation at low temperatures. Moreover, they found that the distinctive behavior of the gold catalysts was due to the presence of nanosized Au particles.In a recent review, Bond and Thompson [5] showed that, in the case of Au-supported catalysts, factors such as Au particle size, preparation method, pretreatment conditions, and choice of the support play an important role in the CO oxidation activity of the final catalyst. Indeed, when nanoparticles of Au are deposited on TiO 2 , [4b, 6a] Co 3 O 4 , [4b, 6b] ZnO, [7] Fe 2 O 3 , [4b, 6a] or MgO, [8] the catalysts are particularly active for the above-mentioned reaction. In contrast, nanoparticles of Au were much less active when other supports were used. [5,9] These results suggest that a synergetic effect between the metal oxide support and Au may exist at the interface such that the metal oxide does not simply act as an inert carrier, but intervenes in the catalytic process.We thought that if gold nanoparticles on the order of 3 to 5 nm were essential for the catalysis (owing to the presence of a large number of surface gold atoms with properties different from those of bulk gold) and if a synergetic mechanism occurs at the gold and metal oxide interface, the characteristics of the metal oxide surface should be of paramount importance. In other words, if the support could be prepared in the form of discrete, well-defined nanoparticles, this should have an influence on the surface electronic properties and consequently on the gold-support interaction.

Comparison of the activity of Au/CeO2 and Au/Fe2O3 catalysts for the CO oxidation and the water-gas shift reactions

“…It has been reported that formation of reactive oxygen species on nanocrystalline ceria is enhanced by the presence of gold [27,50]. Gold on nanoscale ceria is two orders of magnitude more active for the CO oxidation reaction than if deposited on microcrystalline ceria [11]. In this work, ceria was doped with 10 at.% lanthanum, which inhibits the crystal growth of ceria during the calcination step [20,46].…”

“…Gold nanoparticles supported on metal oxides can indeed catalyze low-temperature complete oxidation of hydrocarbons and CO, but also epoxidation reactions and hydrogenations, the NO reduction, and several other reactions as has been reviewed in the recent literature [2,3]. Perhaps the most intensively studied reaction to date is the CO oxidation on gold supported on oxides, such as iron oxide and titania [1,[4][5][6][7], and ceria [8][9][10][11], but also on non-reducible oxides, such as alumina [12][13][14][15] and silica [12]. Activity of nanoparticles of gold on non-oxide supports has also been reported [16].…”

“…There is conflicting information in the literature about the oxidation state of gold during the dry CO oxidation reaction [4,11,14,15,[25][26][27][28][29][30][31][32][33]. There is also an unresolved issue of the importance of gold particle size for this reaction [5,34,35], while a recent theoretical study finds no effect of the type of oxide support if gold clusters with a large number of cus sites are used [36].…”

A comparative study of the effect of addition of CeO x and Li2O on γ-Al2O3 supported copper, silver and gold catalysts in the preferential oxidation of CO

“…It was argued that the active oxygen is supplied by the ceria. Moreover, it was reported that the size of the ceria particles has a great influence on the activity of the catalyst [25]. A detailed study of Gluhoi et al [26][27][28] on the effects of addition of (earth) alkali metals to a Au/Al 2 O 3 catalyst revealed that the main role of the (earth) alkali metals is to stabilize the gold nanoparticles i.e.…”

Characterization of Au-based Catalysts Using Novel Cerium Oxide Supports

“…The nature of the oxide support can have a profound effect on the activity of the catalysts, and Au-catalysts utilizing nanocrystalline oxide supports such as CeO 2 and Y 2 O 3 have been found to possess a significantly greater activity than those dispersed on larger support particles [2]. In the present study, a novel synthesis method involving the use of supercritical CO 2 as an anti-solvent was devised to prepare CeO 2 (scCeO 2 ) support particles.…”