CO oxidation on nanoporous gold: A combined TPD and XPS study of active catalysts

Effect of annealing atmosphere on the thermal coarsening of nanoporous gold films

“…The peaks of metallic Au 0 4f are positively shift to 84.5 and 88.2 eV, respectively, which implies that the chemical state of Au atoms is in the form of Au-O species located between Au 0 and Au + cation [23,26,27]. Similarly, the O 1s peak also shows a high BE shift to 532.6 eV, which is generally observed in carbonates on gold (Au-C O) [17,28,29]. Hence, it can be conceived that the CO molecules adsorbed on the Au surface might exist in a complex form of O-Au-C O [30,31].…”

“…The second set is the peaks at 85.1 and 88.1 eV, and the third is the peak at 86.5 eV, which are assigned to be partially oxidized Au (Au-O) species, such as Au + and Au 3+ [14,[22][23][24], respectively. Accordingly, the fitted curves of O 1s peak yield two types of oxide states at BE of 530.9 and 529.9 eV for bulk oxide and chemisorbed oxygen, respectively [17]. However, the XPS data ( Fig.…”

“…Furthermore, the interaction of CO with Au atoms exhibits a low-temperature adsorption at 200 K, which means that the Au surface is predominantly covered by CO near room temperature. The low-temperature CO adsorption repels the secondary adsorption of O 2 and simultaneously accelerates the dissociation of O 2 [17,29]. Except the above two effects, the reductive reaction should also be considered, where the adsorbed-CO molecules can reduce the Au oxidized species at elevated temperatures due to the better catalytic activity of NPG toward CO oxidation [17,34].…”

“…They found that the ligament size of NPG increased from 30 to 90 nm in He environment at 450 K, while conserved in reactive O 3 environment below the desorption temperature of oxygen (500 K). Recent discoveries showed that the Au thin films annealed in N 2 and Ar atmospheres exhibited an obvious grain growth, whereas those annealed in forming gas (mixture of CO and Ar) preserved the initial grain size [16,17]. Due to the fact that the interaction of adsorbates with surface Au atoms differs with the types of gas species, it seems likely that the growth rate or mechanism will depend on the annealing atmospheres.…”

Nanoporous Metals as Novel Catalysts for Chemical Transformations☆

“…With these studies, it has been revealed that apart from silver, oxygen species such as oxidized hydrocarbon, gold oxide, and subsurface oxygen left during the leaching process play a major role in catalytic activity. 23 Han et al 24 reported an alkaline-pretreated nanoporous gold for CO oxidation ( Figure 10). AuNPore was prepared by free corrosion of Au 42 Ag 58 alloy of 25 mm thickness using nitric acid at room temperature for 24 h. After washing these AuNPore samples with ultrapure water, they were treated with alkaline solution of NaOH or ammonia for 5 or 720 min.…”