Activity and stability of low-content gold–cerium oxide catalysts for the water–gas shift reaction

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

“…A cooperative effect of ceria was invoked to explain why the ceria properties (surface area, crystal size) are crucial both for the Pt-group metals [24] and Au-ceria WGS catalysts [20]. Recently, we were able to document the importance of the interaction between gold and the oxygen of ceria by showing that only the gold species embedded or otherwise associated with ceria [Au n -O-Ce] are the active sites for the WGS reaction [22,23]. The number of these bound gold species that can be carried by ceria is increased as the crystal size of ceria is decreased [23].…”

“…Recently, we were able to document the importance of the interaction between gold and the oxygen of ceria by showing that only the gold species embedded or otherwise associated with ceria [Au n -O-Ce] are the active sites for the WGS reaction [22,23]. The number of these bound gold species that can be carried by ceria is increased as the crystal size of ceria is decreased [23].…”

“…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]. The WGS reaction is much less investigated, but evidence is gradually being collected on the oxidation state of active gold sites, especially on ceria and doped ceria [22,23,37,38], with a theoretical study pointing to stable oxidized gold clusters at ceria oxygen defects as the active sites [39]. The observed reversible reduction/re-oxidation of gold clusters [23,38] as a function of the oxidation potential of the reaction gas mixture is key to our deeper understanding of this system.…”

“…Similar to what is known for the Pt-group metals on ceria [21], the presence of gold greatly enhances the reducibility of the surface oxygen of ceria and the WGS reaction lights off at $100°C. Nanoscale ceria is much more effective in keeping gold dispersed and in an active state [20,22,23]. A cooperative effect of ceria was invoked to explain why the ceria properties (surface area, crystal size) are crucial both for the Pt-group metals [24] and Au-ceria WGS catalysts [20].…”

H 2 Production and Fuel Cells

“…48 Pure ceria is a very poor WGS catalyst, but the properties of this oxide were found to be crucial for the observed activity of the Au-CeO 2 catalysts. 43,49 Several models have been proposed for explaining the unusual catalytic properties of gold supported on oxides: 41,42,45 From special chemical properties resulting from the limited size of the active gold particles (usually less than 5 nm), to the effects of metal:support interactions. In particular, it has been suggested by several authors that the active phase in Au-CeO 2 catalysts are AuO x nanoparticles or more specifically cationic Au δ+ species.…”