Strong metal–support interaction in novel core–shell Au–CeO₂nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation

Abstract

Yolk-shell Au/CeO2 (Y-Au/CeO2) and encapsulated Au/CeO2 (E-Au/CeO2) nanocatalysts were prepared by using silica templates. A strong metal-support interaction (SMSI) in the Au/CeO2 nanostructures induced by different pretreatment atmospheres and its influence on CO oxidation were studied. E-Au/CeO2 pretreated in O2 had the best performance, followed by Y-Au/CeO2 pretreated in O2, Y-Au/CeO2 pretreated in H2, and E-Au/CeO2 pretreated in H2. The reasons for the different activities were discussed. There were two kinds of strong metal-support interactions (SMSI) between Au and CeO2 termed as R-SMSI (pretreated in reductive atmosphere) and O-SMSI (pretreated in oxidation atmosphere). Because of the smaller size of the Au and the larger contact area, both the R-SMSI and O-SMSI of E-Au/CeO2 were larger than those of Y-Au/CeO2. The O-SMSI was accompanied by the formation of cationic Au species that were beneficial to the enhancing of activity. As expected, the activity of E-Au/CeO2 pretreated in O2 with a Au size less than 5 nm was higher than that of Y-Au/CeO2 pretreated in O2 with 25 nm Au. However, it is surprisingly found that the activity of Y-Au/CeO2 pretreated in H2 with 25 nm Au was higher than that of E-Au/CeO2 pretreated in H2 with a Au size less than 5 nm. R-SMSI resulted in the formation of a AuCe alloy that had a negative effect on the activity. Compared with E-Au/CeO2 pretreated in H2, Y-Au/CeO2 pretreated in H2 exhibited a smaller relative content of the AuCe alloy, leading to a better activity of Y-Au/CeO2 pretreated in H2.

Pretreatment Effect on Ceria‐Supported Gold Nanocatalysts for CO Oxidation: Importance of the Gold–Ceria Interaction

“…[15] Wang et al studied the influenceo ft he pretreatment on the Au-CeO 2 interaction for CO oxidation and found that O 2 pretreatment had ap ositive effect on the activity. [11] These results explained the Au-CeO 2 interaction pretty well. However, the Au-CeO 2 interaction associated with the pretreatment activation process has not been well understood.…”

“…[39] Recently,W ang et al reported that H 2 -pretreated encapsulated Au/CeO 2 nanocatalysts were inactive for CO oxidation. [11] Presumably,t he pretreatment leads to ar edox cycle of M n + and M m + as suggested for Au/CeO 2 by Widmanne tal. [40] There are severalp ossible parallel reaction pathways on the catalyst surface for CO oxidation: one is on Au NPs,a nother is on the hollow CeO 2 substrate, and the third one is at the Au-CeO 2 interface.…”

“…[29] Notably,n op eaks related to Au were observed (the metallic Au phase gives ac haracteristic XRD peak at 2 q = 38.48)b ecause of the small size and small amountofA uN Ps. [11] Catalytic properties in CO oxidation Accordingt ot he results of previous studies,A u/CeO 2 catalysts pretreated under different atmospheres showed different CO oxidation activities because of different metal-support interactions. [11,30] TheS n samples pretreated under O 2 , N 2 ,a nd 10 %C O/Ar were denoted as On,N n,a nd Cn,r espectively (n = 1a nd 3).…”

“…[11] Catalytic properties in CO oxidation Accordingt ot he results of previous studies,A u/CeO 2 catalysts pretreated under different atmospheres showed different CO oxidation activities because of different metal-support interactions. [11,30] TheS n samples pretreated under O 2 , N 2 ,a nd 10 %C O/Ar were denoted as On,N n,a nd Cn,r espectively (n = 1a nd 3). Thef ollowing sequence of CO oxidation activityw as observed:O 3( T 100 = 74 8C) > O1 (T 100 = 93 8C) > N3 (T 100 = 142 8C) > N1 (T 100 = 161 8C) > C3 (T 100 = 167 8C) > C1 (T 100 = 189 8C; Figure 5).…”

“…[4][5][6] Thes tudy of CO oxidation on Au/CeO 2 has become ap roblem because many factorsc an influence the activity,s ucha st he size andt he valence state of Au, [7][8][9][10] the morphology of CeO 2 ,and the Au-CeO 2 interaction. [3,11] Fors upported metal catalysts,t here has been interest in the study of the influence of the metal-support interaction on catalytic performance. [12,13] Cargnello et al reported that the properties of the metal-CeO 2 interface sites can change the interactions between the metal and CeO 2 in CO oxidation.…”