Effect of Indium Doping of γ-Alumina on the Stabilization of PtSn Alloyed Clusters Prepared by Surface Organostannic Chemistry

Abstract

The control of the atomic-scale properties of highly dispersed multimetallic particles represents a challenging question for the optimal use of metallic active centers in nanoscience. In particular, improving the formation of Pt x Sn alloyed clusters on γ-alumina of a size close to 1 nm with a high Sn0/Pt ratio represents a crucial step toward more selective heterogeneous catalysts. For that purpose, bimetallic SnPt-based and trimetallic SnPtIn-based catalysts were prepared by surface organostannic chemistry on monometallic Pt and bimetallic PtIn-based catalysts. These systems were characterized by a multitechnique approach combining CO chemisorption, temperature programmed reduction, scanning transmission electron microscopy, Mössbauer spectroscopy, and X-ray absorption spectroscopy. The nature of the PtSn phase in trimetallic SnPtIn-based catalysts is found to strongly depend on the way indium is initially introduced in the parent catalyst, by either wet impregnation or coprecipitation with aluminum precursor. The key role of In3+ species on the formation of PtSn alloyed clusters is revealed. By using density functional theory calculations, we give a rational interpretation of the experimental results and provide an atomic scale description of Pt x Sn y /γ-Al2O3 systems, with or without In3+ on the alumina surface. The formation of In–Pt, In–Sn, and O–Sn bonds is indeed favored when In3+ is present in the support. This work proposes an original approach for stabilizing Pt x Sn alloyed clusters with an elevated Sn0/Pt ratio and highly dispersed on γ-alumina using indium as “third element” introduced as In3+ on the support.

Density functional theory simulations of complex catalytic materials in reactive environments: beyond the ideal surface at low coverage

“…11). 152 While tin is shown to decrease the metal-support interaction as compared to pure platinum, indium compensates part of the interaction loss, which results in a stabilization of the bimetallic PtSn nano-cluster.…”

Atomistic Models for Highly‐Dispersed PtSn/γ‐Al2O3 Catalysts: Ductility and Dilution Affect the Affinity for Hydrogen

“…To make progress in this area and allow a better control of the active phase, the elaboration of structural models for bimetallic platinum‐tin subnanometric particles supported on γ‐alumina, is of fundamental and practical importance. Density functional theory (DFT) calculations are useful in that respect, due to the challenging characterization of supported clusters, that are often sub‐nanometric and non‐regular in shape . Significant amount of work has been devoted so far for the proposal of relevant dispersed monometallic Pt/Al 2 O 3 models, particularly in the case of the gamma polymorph of alumina .…”

Catalytic Reforming: Methodology and Process Development for a Constant Optimisation and Performance Enhancement

“…Even with this controlled deposition, the effect of indium localization, either on the support by impregnation or into the support by co-precipitation with aluminium precursor, leads to a maximization of PtSn alloy formation when indium is introduced in the support, with a 35% fraction of tin alloyed with platinum for a SnPt/Al 2 O 3 In-Cl catalyst. Finally, the combination of DFT calculations with the 119 Sn Mössbauer and X-ray absorption spectroscopies observations allowed to rationalize this particular behaviour [23] and to reveal the key role of In 3+ species on the formation of Pt x Sn alloys, by stabilizing Pt x Sn clusters thanks to Sn 0 -In 3+ bond formation.…”

“…The H/Pt ratio exceeding 1 -often observed in experimental analysis conditions [34,35] -is rationalized by this reconstruction process. The electrostatic charge analysis reveals that a hydride phase is obtained for the CUB structure, with the partial loss of the metallic nature of DFT results of the simulation of model reforming catalysts: a) calculated binding energy (including Pt-Pt cohesion and metal-support interaction) of Pt n clusters, isolated or supported on c-Al 2 O 3 [25]; the most stable Pt 3 cluster supported on chlorinated c-Al 2 O 3 is shown in inset; b) effect of hydrogen pressure on the morphology change of supported Pt 13 [33]; c) relative stabilities of adsorbed ethylene (H 2 CCH 2 ) and ethylidyne (CCH 3 ) on Pt 13 supported cluster at various J = P(H 2 )/P(C 2 H 6 ) values; insets: illustrations of adsorbed ethylene and ethylidyne at J = 1 [42]; d) models of supported PtSn catalysts, without (top) or with (bottom) indium incorporated in the support [23].…”

“…We recently started to undertake this by focusing on PtSn formulations, eventually with Indium as co-doping element present in the support as In 3+ state (Fig. 22d), to shed new light on the experimental results explained in the previous section [23]. While tin is shown to decrease the metal-support interaction as compared to pure platinum, indium helps to compensate part of the interaction loss resulting in a stabilization of the bimetallic PtSn nano-cluster.…”