Probing the Formation Mechanism and Chemical States of Carbon-Supported Pt−Ru Nanoparticles by in Situ X-ray Absorption Spectroscopy

Abstract

The understanding of the formation mechanism of nanoparticles is essential for the successful particle design and scaling-up process. This paper reports findings of an X-ray absorption spectroscopy (XAS) investigation, comprised of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions, to understand the mechanism of the carbon-supported Pt-Ru nanoparticles (NPs) formation process. We have utilized Watanabe's colloidal reduction method to synthesize Pt-Ru/C NPs. We slightly modified the Watanabe method by introducing a mixing and heat treatment step of Pt and Ru oxidic species at 100 degrees C for 8 h with a view to enhance the mixing efficiency of the precursor species, thereby one can achieve improved homogeneity and atomic distribution in the resultant Pt-Ru/C NPs. During the reduction process, in situ XAS measurements allowed us to follow the evolution of Pt and Ru environments and their chemical states. The Pt LIII-edge XAS indicates that when H2PtCl6 is treated with NaHSO3, the platinum compound is found to be reduced to a Pt(II) form corresponding to the anionic complex [Pt(SO3)4]6-. Further oxidation of this anionic complex with hydrogen peroxide forms dispersed [Pt(OH)6]2- species. Analysis of Ru K-edge XAS results confirms the reduction of RuIIICl3 to [RuII(OH)4]2- species upon addition of NaHSO3. Addition of hydrogen peroxide to [RuII(OH)4]2- causes dehydrogenation and forms RuOx species. Mixing of [Pt(OH)6]2- and RuOx species and heat treatment at 100 degrees C for 8 h produced a colloidal sol containing both Pt and Ru metallic as well as ionic contributions. The reduction of this colloidal mixture at 300 degrees C in hydrogen atmosphere for 2 h forms Pt-Ru nanoparticles as indicated by the presence of Pt and Ru atoms in the first coordination shell. Determination of the alloying extent or atomic distribution of Pt and Ru atoms in the resulting Pt-Ru/C NPs reveals that the alloying extent of Ru (JRu) is greater than that of the alloying extent of Pt (JPt). The XAS results support the Pt-rich core and Ru-rich shell structure with a considerable amount of segregation in the Pt region and with less segregation in the Ru region for the obtained Pt-Ru/C NPs.

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

“…Based on a recent publication, we estimate that the extent of dispersion/alloying for both metals in this sample is only ca. 42% (where a value of 100% represents a true random bi-metallic mixture) [85]. In a previous study on polymer protected Pt-Pd bi-metallic samples, Toshima et al [86] determined the nature of their bi-metallic samples by comparing their EXAFS-derived coordination numbers to cuboctahedral-based models with different degrees of Pt-Pd dispersion.…”

Size and composition for 1–5nm Ø PtRu alloy nano-particles from Cu Kα X-ray patterns

“…In short, metal salts of PtCl 4 and RuCl 3 (Alfa Aesar, 99.9% metals basis) were dissolved in 50 mL of ethylene glycol containing NaOH. The solutions were stirred for 30 min., subsequently heated and refluxed for 3 h at 160 • C. Dark brown solutions containing either Pt or Pt-Ru colloids were formed rapidly (<15 min.)…”

“…4 (Alfa Aesar, 99.9% metal basis) were dissolved in 25 mL of ethylene glycol containing 0.07 M NaOH. The solution was stirred for 30 min at room temperature, and subsequently heated under reflux at 160 • Cf o r 1 h. A dark brown solution containing Pt colloids was formed in this manner.…”

“…Significant efforts have been devoted to their theoretical understanding, as well as synthesis and characterization [2][3][4][5][6][7][8][9][10].A sn o single investigation method provides the required detailed structural information on bi-metallic nano-particles, the combination of several analytical methods is needed. Those methods include X-ray absorption spectroscopy (XAS) [3,4], nuclear magnetic resonance (NMR) [5], infrared spectroscopy [6,7], X-ray photoelectron spectroscopy (XPS) [8] and X-ray diffraction (XRD) [9][10][11]. We wish here to develop further the application of XRD because of the apparent simplicity of its application.…”

Design of Pt‐Based Bimetallic Alloys for the Oxidation of H2O2: A Combined Computational and Experimental Approach

“…%) with a Pt/M atomic ratio of close to 1:1 (by ICP-AES) were successfully prepared by using a modified Watanabe method. [7] As mentioned above, we calculated the energy barriers for the dehydrogenation steps in the H 2 O 2 -oxidation reaction for a number of PtÀM (111) alloys to reveal the dehydrogenation barriers relative to various Pt e d values and OH-adsorption energies on an M site. In the experimental section, by using linear scan voltammetry (LSV), the ki- (111), H A would rotate to face the nearby OH group).…”