Preparation and Investigation of Pd and Bimetallic Pd-Sn Nanocrystals on γ-Al2O3

Abstract

One of the key factors for producing highly dispersed controlled nanoparticles is the method used for metal deposition. The decomposition of metal-organic precursors is a good method for deposition of metal nanoparticles with very small sizes and narrow size distributions on the surface of various supports. The preparation process of Pd and bimetallic Pd-Sn nanoparticles supported onto γ‑Al2O3 is considered. The samples were prepared by diffusional co-impregnation of the γ‑Al2O3 support by using organometallic Pd(acac)2 and Sn(acac)2Cl2 precursors. To achieve the formation of Pd and bimetallic Pd-Sn nanoparticles on the support surface, the synthesized samples were then subjected to thermal decomposition under Ar (to decompose the organometallic bound to the surface while keeping the formed nanoparticles small) followed by an oxidation in O2 (to eliminate the organic compounds remaining on the surface) and a reduction in H2 (to reduce the nanoparticles oxidized during the previous step). A combination of methods (ICP-OES, TPR-H2, XPS, TEM/EDX) was used to compare the physical-chemical properties of the synthesized Pd and bimetallic Pd-Sn nanoparticles supported on the γ‑Al2O3. The three samples exhibit narrow size distribution with a majority on nanoparticles between 3 and 5 nm. Local EDX measurements clearly showed that the nanoparticles are bimetallic with the expected chemical composition and the measured global composition by ICP-OES. The surface composition and electronic properties of Pd and Sn on the γ-Al2O3 support were investigated by XPS, in particular the chemical state of palladium and tin after each step of thermal decomposition treatments (oxidation, reduction) by the XPS method has been carried out. The reducibility of the prepared bimetallic nanoparticles was measured by hydrogen temperature programmed reduction (TPR-H2). The temperature programmed reduction TPR-H2 experiments have confirmed the existence of strong surface interactions between Pd and Sn, as evidenced by hydrogen spillover of Pd to Sn (Pd-assisted reduction of oxygen precovered Sn). These results lead us to propose a mechanism for the formation of the bimetallic nanoparticles.

Alkaline Formate Oxidation with Colloidal Palladium–Tin Alloy Nanocrystals

“…The O 1s spectra, provided as Figure S1b, further supports the oxidized metal character. This more oxidized surface state for Sn is due to the high oxophilic nature of Sn, distinct to the Pd character …”

“…This more oxidized surface state for Sn is due to the high oxophilic nature of Sn, distinct to the Pd character. 56 Transmission electron microscopy (TEM) observations for the alloy catalysts are depicted in Figure 2 with the corresponding micrographs and energy-dispersive spectrometry (EDS) mappings. Figure 2a shows the micrograph of the Pd 85 Sn 15 /C catalyst, which shows an even distribution of alloy nanoparticles with an average size of ∼6 nm over the carbon support with a near-spherical morphology.…”

Easy preparation of small crystalline Pd2Sn nanoparticles in solution at room temperature

“…5). 41 The minor contribution was attributed to metallic tin, Sn(0), presumably located at the core of the nanoparticles in the Pd 2 Sn alloy. The major contribution was assigned to Sn 4+ coming from the tributyltin fragments at the surface of the NPs and grafted onto the silica surface.…”