Stabilizing Oxide Nanolayer via Interface Confinement and Surface Hydroxylation

Abstract

Surface hydroxylation over oxide catalysts often occurs in many catalytic processes involving H2 and H2O, which is considered to play an important role in elementary steps of the reactions. Here, monolayer CoO and CoOH x nanoislands on Pt(111) are used as inverse model catalysts to study the effect of surface hydroxylation on the stability of Co oxide overlayers in O2. Surface science experiments indicate that hydroxyl groups formed on CoO nanoislands produced by deuterium-spillover can enhance oxidation resistance of the Co oxide nanostructures. Theoretical calculation shows that the interfacial adhesion between CoO and Pt is linearly strengthened with the increasing hydroxylation degree of CoO surface. Thus, the interface confinement effect between CoO and Pt can be enhanced by the surface hydroxylation due to the more reduced Co ions and stronger Co–Pt bonding at the CoOH x /Pt interface.

Adsorption and Oxidation of CO on Co3O4/Ir(100) Thin Films

“…The corresponding O 1s spectrum is fitted with two peaks at 530.6 and 529.5 eV, as shown in Figure d. Considering that CoO x nanostructures are easily hydroxylated on noble metal surfaces even under the UHV conditions by background H 2 , , we considered if the peak at 530.6 eV may be due to surface hydroxyl groups. To test this, we exposed a fresh cobalt oxide surface to 5 L of water at 300 K. The corresponding O 1s spectrum in Figure S1 shows a peak at 531.7 eV, i.e., at considerably higher binding energy than the O 1s peak at 530.6 eV, which we assigned to the lower O species of the cobalt oxide.…”

Hydroxide Structure-Dependent OH Promotion Mechanism over a Hydroxylated CoOx/Pt(111) Catalyst toward CO Oxidation

“…After the exposure of CoO x nanoislands on Pt(111) to D 2 , HREELS results (Figure 1d: I and II) show strong signals at 2649 and 3596 cm −1 , which are ascribed to the stretching vibration of OD and OH, respectively. 43 In addition, the weak signal at 2052 cm −1 is assigned to CO (from background atmosphere) adsorbed at top sites of bare Pt(111). 67 Accordingly, the corresponding O 1s peak (Figure 1e: II) 41,43,55,56 For the sample exposed to D 2 O, the HREELS results (Figure 1d: III) are similar to H h -CoO x /Pt.…”

“…43 In addition, the weak signal at 2052 cm −1 is assigned to CO (from background atmosphere) adsorbed at top sites of bare Pt(111). 67 Accordingly, the corresponding O 1s peak (Figure 1e: II) 41,43,55,56 For the sample exposed to D 2 O, the HREELS results (Figure 1d: III) are similar to H h -CoO x /Pt. However, XPS measurements show that the total O 1s peak area increases by 20% after exposure to D 2 O (Figure 1f).…”

“…Designing multicomponent catalysts, such as constructing metal–oxide interface, is an effective strategy to achieve excellent catalytic performance. − In many cases, however, the active structure of the catalysts often evolves under reaction conditions, which can result in activation or deactivation of catalysts or changes in product selectivity. − H 2 or H 2 O molecules are often present as reactants or products in many catalytic reactions, such as the water–gas shift (WGS) reaction, − CO 2 hydrogenation, ,,− and Fischer–Tropsch synthesis, − or exist in the reaction as impurities. , The introduction of H 2 O or H 2 can lead to surface hydroxylation of many metal oxides, such as cobalt oxides, − zinc oxides, − titanium oxides, , and nickel oxides, through dissociative adsorption of H 2 O or hydrogen spillover. − The surface hydroxylation has been shown to be correlated with the high reactivity of metal oxides in WGS, , acetylene hydrogenation, and CO oxidation reactions …”

Confinement-Induced Indium Oxide Nanolayers Formed on Oxide Support for Enhanced CO2 Hydrogenation Reaction

“…Although a similar interaction is also present between a guest atom/molecule/cluster and an open host surface, confinement by the open surface/interface has not been recognized as widely as that in an enclosed space. − Recent results show that metastable guest nanolayers containing CUSs can be stabilized on an open host surface, which has been exemplified by the formation of defective oxide nanoislands on noble metal surfaces. − Thus, the open solid surface may exert a similar confinement effect to stabilize CUSs as the enclosed nanospace. − It is of more significance to achieve high-density coordinatively unsaturated active sites confined on the open surface of the most used supports such as oxides and to understand the oxide–oxide interface confinement effect. ,− …”