Steering the formation of supported Pt–Sn nanoalloys by reactive metal–oxide interaction

Abstract

The formation of a supported Pt-Sn nanoalloy upon reactive metal-oxide interaction between Pt nanoparticles and a Sn-CeO 2 substrate has been investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy in combination with density functional modeling. It was found that Pt deposition onto a Sn-CeO 2 substrate triggers the reduction of Sn 2+ cations yielding Pt-Sn nanoalloys at 300 K under ultra-high vacuum conditions. Three distinct stages of Pt-Sn nanoalloy formation were identified associated with the growth of (I) ultra-small monometallic Pt particles on a Sn-CeO 2 substrate, (II) Pt-Sn nanoalloys on a Sn-CeO 2 substrate, and (III) Pt-Sn nanoalloys on a stoichiometric CeO 2 substrate. These findings suggest the existence of a critical size of monometallic Pt particles above which the formation of a Pt-Sn nanoalloy becomes favorable. In this respect, density functional modeling revealed a strong dependence of the formation energy of the Pt x Sn nanoalloy on the size of the Pt particle. Additionally, the thermodynamically favorable bulk and surface Pt/Sn stoichiometries were identified as two parameters that determine the composition of the supported Pt-Sn nanoalloys and limit the extraction of Sn 2+ from the Sn-CeO 2 substrate. Primarily, the formation of a bulk Pt 3 Sn alloy phase drives the growth of the Pt-Sn nanoalloy upon Pt deposition at 300 K. Upon annealing, Sn segregation on the surface of the Pt-Sn nanoalloy promotes further extraction of Sn 2+ until the thermodynamically stable Pt/Sn concentration ratios of 3for the bulk and approximately 1.6 for the surface are reached.

Pt‐Sn Nanoparticles Supported on Carbon Nanodots as Anode Catalysts for Alcohol Electro‐oxidation in Acidic Conditions

“…Neitzel et al. prepared Pt‐Sn nanoparticles with very small particles sizes which were supported on a reactive metal oxide (CeO 2 ) by depositing Pt on Sn‐CeO 2 under ultra‐high vacuum to facilitate reduction of Sn 2+ to yield Sn blended with Pt. The vacuum enabled the complete reduction of all the ions to metallic Pt and Sn.…”

Oxidation of Sn at the Cluster–Support Interface: Sn and Pt–Sn Clusters on TiO2(110)

“…This shift to higher binding energy is attributed to the formation of a Sn–Pt alloy, given that the metallic Sn­(3d 5/2 ) binding energy is 0.3–0.6 eV higher in Pt–Sn alloy nanoparticles; , a similar shift of +0.2–0.3 eV is observed for Sn alloyed into Pt(111) surfaces. ,, The loss of the SnO x peak is ascribed to the diffusion of Sn away from the interface with TiO 2 and into the interior of the cluster in order to increase the favorable interactions between Pt and Sn atoms . The relatively large heat of formation (30–80 kJ/mol) for intermetallic PtSn compounds favors alloying over the monometallic phases. − Similarly, the deposition of 0.13 ML Pt on 0.13 ML Sn causes a decrease in the SnO x intensity and a smaller shift in the Sn­(3d 5/2 ) binding energy of +0.1 eV. For both the low and high coverage surfaces, the Sn­(3d 5/2 ) binding energy of SnO x also shifts by −0.3 eV after Pt deposition and could be related to disruption of the SnO x phases following the addition of Pt atoms.…”

“…The Pt­(4f) spectra for pure Pt and Sn on Pt (θ Pt,Sn = 0.05 and 0.13 ML) show that there is a small 0.2 eV shift to higher binding energy after Sn deposition on the Pt clusters for both coverages (Figure S2). Since the surface of the clusters is expected to be Sn-rich based on the lower surface free energy of Sn compared to Pt, the shift in the Pt­(4f) peaks could be attributed in part to a surface core level shift due to the loss of the low binding energy, undercoordinated Pt atoms at the surface. , However, a positive shift (∼+0.3 eV) in Pt­(4f 7/2 ) binding energy is also consistent with Pt–Sn alloying, ,,,,,− which is expected to occur, given the ability of Pt–Sn systems to alloy over a wide range of compositions …”

Nanoscale architecture of ceria-based model catalysts: Pt–Co nanostructures on well-ordered CeO2(111) thin films

“…We believe that the mechanism of Co 2+ reduction is associated with the reactive metal-support interaction (RMSI) [45,46] between the Pt and the Co-CeO2 solid solution coupled with the reduction of Co 2+ to Co 0 followed by its diffusion to Pt. The similar effect was also observed upon deposition of Pt onto Sn-doped CeO2(111) film at 300 K in UHV [45]. The reactive interaction of Pt with Sn 2+ led to the reduction of Sn 2+ yielding supported Pt-Sn nanoalloys.…”