Surface oxidation-induced restructuring of liquid Pd–Ga SCALMS model catalysts

Abstract

We have examined model systems for the recently reported Pd-Ga Supported Catalytically Active Liquid Metal Solutions (SCALMS) catalysts using near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) under oxidizing conditions. Gallium is...

Unravelling the Surface Oxidation-Induced Evolution of the Electronic Structure of Gallium

“…For the Ga/SiO x /Si that has been oxidized for 10 min, the oxide contribution to the Ga 2p 3/2 (Ga 3d) line is in agreement with the formation of a 1.4 ± 1.1 Å (2.9 ± 1.1 Å) Ga 2 O 3−δ layer, which is less than 5.6 Å, i.e., the thickness of monolayer Ga 2 O 3 , indicating only a partially oxidized Ga surface. The formation of submonolayer gallium oxide layers under these conditions is consistent with previous studies. , For the sample that has been oxidized for 60 min, the film thickness increased to 6.8 ± 1.4 Å (8.8 ± 1.4 Å), i.e., roughly equivalent or representing slightly more than a monolayer of Ga 2 O 3 . , The final point, the sample after 240 min oxidation, shows a thickness of 8.6 ± 0.4 Å (9.1 ± 0.4 Å), indicating the oxygen-diffusion-limited formation of a second Ga oxide monolayer (Figure b, Tables S3 and S4). The oxide film thickness of the sample exposed to ambient oxidations for 1 month is estimated to be 35 ± 1 Å, indicating the formation of approximately 6 monolayers of Ga oxide at the sample surface (Table S5).…”

“…11,12 For the sample that has been oxidized for 60 min, the film thickness increased to 6.8 ± 1.4 Å (8.8 ± 1.4 Å), i.e., roughly equivalent or representing slightly more than a monolayer of Ga 2 O 3 . 18,32 The final point, the sample after 240 min oxidation, shows a thickness of 8.6 ± 0.4 Å (9.1 ± 0.4 Å), indicating the oxygendiffusion-limited formation of a second Ga oxide monolayer (Figure 2b, Tables S3 and S4). The oxide film thickness of the sample exposed to ambient oxidations for 1 month is estimated to be 35 ± 1 Å, indicating the formation of approximately 6 monolayers of Ga oxide at the sample surface (Table S5).…”

“…Ga-based liquid metals with a surface passivating gallium oxide shell are utilized in several applications, e.g., molecular electronics and thermoelectrics – as well as thermal indicators for drug delivery. , Recently, it has also been frequently employed as a matrix for liquid metal catalyst developments. The high dispersity of transition metals in Ga was observed for several Ga x M y composites (M: Pt, Pb, Rh) which led to the development of supported catalytically active liquid metal solution (SCALMS). – ,– SCALMS is a new class of catalysts, which often comprises a liquid metal matrix (Ga) containing diluted metal active sites (M).…”

Preparation of geometrically highly controlled Ga particle arrays on quasi-planar nanostructured surfaces as a SCALMS model system

“…However, a mixture of a GaPd alloy and Pd 0 seems likely due to the broad signal. 23 The exchange of Ga with Pt leads to the formation of a GaPt intermetallic compound (IMC, PtGa 4f doublet at 74.3 eV and 71.0 eV with Δ = 3.33 eV), 24 as expected from the phase diagram of GaPt. 25 The main signal in the Pt 4f region results from Pt incorporated into gallium oxide, where Pt is positively charged.…”

Impact of Catalysis-Relevant Oxidation and Annealing Treatments on Nanostructured GaRh Alloys

“…42,43 Assuming a simple GaO x /Ga bilayer model with a closed GaO x film that homogeneously covers the Ga, the oxide film thickness after 240 min exposure to 1 × 10 −6 mbar partial pressure of oxygen is estimated to be (7.3 ± 1.0) and (9.0 ± 1.0) Å calculated from Ga 2p 3/2 and Ga 3d, respectively (see also SI 1.3 for details), which corresponds to the thickness between one and two monolayers of GaO x (see also quantified results of the Ga 3d and Ga 2p 3/2 fits in the SI, Tables S1 and S2). 42 The formation of ultrathin GaO x layers was observed previously for Ga, GaPd, and GaPt oxidized in 10 −5 −10 −7 mbar partial pressures of oxygen and was explained by limited mass transport of oxygen into the subsurface of Ga. 26,42,44 The Rh 3d 5/2 spectra seem to be unaffected by the oxidation treatment and can still be described by one spectral contribution remaining at 307.6 eV (see Figure 1c), mainly indicating a preservation of the chemical structure of the Rh within the GaRh alloy despite exposure to 1 × 10 −6 mbar O 2 . We assume that, as in our previous study, 27 the feature at 307.6 eV in the spectrum of the 7 at.…”