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. 2022 Jan 6;12(2):183.
doi: 10.3390/nano12020183.

Water Formation Reaction under Interfacial Confinement: Al0.25Si0.75O2 on O-Ru(0001)

Jorge Cored  1   2 , Mengen Wang  2   3 , Nusnin Akter  2   3 , Zubin Darbari  2   3 , Yixin Xu  2   3 , Burcu Karagoz  2 , Iradwikanari Waluyo  4 , Adrian Hunt  4 , Dario Stacchiola  2 , Ashley Rose Head  2 , Patricia Concepcion  1 , Deyu Lu  2 , Jorge Anibal Boscoboinik  2
Affiliations

Water Formation Reaction under Interfacial Confinement: Al0.25Si0.75O2 on O-Ru(0001)

Jorge Cored et al. Nanomaterials (Basel). .

Abstract

Confined nanosized spaces at the interface between a metal and a seemingly inert material, such as a silicate, have recently been shown to influence the chemistry at the metal surface. In prior work, we observed that a bilayer (BL) silica on Ru(0001) can change the reaction pathway of the water formation reaction (WFR) near room temperature when compared to the bare metal. In this work, we looked at the effect of doping the silicate with Al, resulting in a stoichiometry of Al0.25Si0.75O2. We investigated the kinetics of WFR at elevated H2 pressures and various temperatures under interfacial confinement using ambient pressure X-ray photoelectron spectroscopy. The apparent activation energy was lower than that on bare Ru(0001) but higher than that on the BL-silica/Ru(0001). The apparent reaction order with respect to H2 was also determined. The increased residence time of water at the surface, resulting from the presence of the BL-aluminosilicate (and its subsequent electrostatic stabilization), favors the so-called disproportionation reaction pathway (*H2O + *O ↔ 2 *OH), but with a higher energy barrier than for pure BL-silica.

Keywords: aluminosilicate bilayer film; ambient pressure X-ray photoelectron spectroscopy; density functional theory; interfacial confinement; nanoreactor; reaction pathway; water formation reaction.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Atomic structures of (a) (SiO2)8/4O/Ru and (b) (Al0.25Si0.75O2)8/3O/Ru(0001). Side (c) and top (d) views of the bilayer aluminosilicate film growth on Ru(0001) with two H+ bound to the bridging O in (Al–O−)–Si to compensate the framework charge [i.e., (H0.25Al0.25Si0.75O2)8/3O/Ru(0001)]. The black rectangle on the top view (d) indicates the unit cell. Color code: Ru (silver), Si (yellow), Al (blue), H (white), O in aluminosilicate (red), and O chemisorbed on Ru (pink).
Figure 2
Figure 2
Dual-path reaction mechanism of water formation reaction (WFR) reported on the Pt(111) surface. * indicates the species adsorbed on the platinum surface.
Figure 3
Figure 3
Si 2p (a) and O 1s (b) core level spectra before and after reaction at 450 K in 0.1 Torr of H2; (c) deconvolution of the O 1s core level spectrum before reaction.
Figure 4
Figure 4
Core level shifts (solid symbols) for Si 2p and O 1s (Si–O–Si and Si–O–Al components) as a function of time at 450 K in 0.1 Torr of H2. The coverage of chemisorbed O (open circles) is also shown for comparison.
Figure 5
Figure 5
(a) Plot of oxygen coverage vs. time at 380, 400, 420, and 450 K; (b) Arrhenius plots for WFR at the BL-aluminosilicate/Ru(0001) interface (this work, blue triangles), compared to similar prior work on bare Ru(0001) (black circles) and BL-silica/Ru(0001) (red squares).
Figure 6
Figure 6
Potential energy diagram for the WFR at the BL-aluminosilicate/Ru(0001) interface via (a) first hydrogen addition step (*H + *O ↔ *OH) and (b) disproportionation pathway (*H2O + *O ↔ 2 *OH); (c) Potential energy diagram for the disproportionation pathway (*H2O + *O ↔ 2 *OH) at the silica/Ru(0001) interface. Color code: Ru (silver), Si (yellow), Al (blue), H adsorbed on aluminosilicate (small white), O in aluminosilicate (red), *O chemisorbed on Ru (pink), and *H adsorbed at the aluminosilicate/Ru(0001) interface that react with *O (large white).
Figure 7
Figure 7
WFR reaction evolution at 420 K and variable pressure conditions (0.1–0.5 Torr H2). Vertical lines indicate the endpoint of the reaction at each working pressure.
Figure 8
Figure 8
(a) Initial WFR reaction evolution at different temperatures (380–450 K) at 0.1 Torr H2 and (b) dependence between the initial rate and the H2 pressure.
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