Tuning Pd-to-Ag Ratio to Enhance the Synergistic Activity of Fly Ash-Supported Pd_xAg_y Bimetallic Nanoparticles

Abstract

Fly ash (FA)-supported bimetallic nanoparticles (Pd x Ag y /FA) with varying Pd:Ag ratios were prepared by coprecipitation of Pd and Ag involving in situ reduction of Pd­(II) and Ag­(I) salts in aqueous medium. All the supported nanoparticles were thoroughly characterized with the aid of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM)), and elemental analyses, which include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). A gradual broadening and shifting of PXRD peaks, ascribable to Ag, to higher angles with an increase in the Pd:Ag ratio affirms the alloying of interface between Pd and Ag nanoparticles. The coexistence of Pd and Ag was further confirmed by EDS elemental mapping as well as by the presence of bimetallic lattices on the FA surface, as evident from the high-resolution TEM analysis. The dependency of crystallite size and average size of bimetallic nanoparticles on Ag loading (mol %) was elucidated with the help of a combination of PXRD and TEM studies. Based on XPS analysis, the charge transfer phenomenon between contacting Pd−Ag sites could be evident from the shifting of 3d core electron binding energy for both Pd and Ag compared with monometallic Pd and Ag nanoparticles. Following a pseudo-first-order reaction kinetics, all the nanocatalysts were able to efficiently reduce 4-nitrophenol into 4-aminophenol in aqueous NaBH4. The superior catalytic performance of the bimetallic nanocatalysts (Pd x Ag y /FA) over their monometallic (Pd100/FA and Ag100/FA) analogues has been demonstrated. Moreover, the tunable synergistic effect of the bimetallic systems has been explored in detail by varying the Pd:Ag mol ratio in a systematic manner which in turn allowed us to achieve an optimum reaction rate (k = 1.050 min–1) for the nitrophenol reduction using a Pd25Ag75/FA system. Most importantly, all the bimetallic nanocatalysts explored here exhibited excellent normalized rate constants (K ≈ 6000–15,000 min–1 mmol–1) compared with other supported bimetallic Pd–Ag nanocatalysts reported in the literature.

Grafting of CuCo Alloy Nanoparticles on g-C3N4 Sheet: An Efficient Strategy for Solar-Driven Photocatalytic Degradation of Ibuprofen and H2 Gas Evolution by Water Splitting

“…In the above two studies, we found that in hydrogen gas evolution and in the photocatalytic degradation study of IBU, CuCo(3:1) ratio came out to be the best catalyst out of the other two ratios, i.e., CuCo(1:1) and CuCo(1:3). This is because, for attaining an optimum synergistic effect in bimetallic catalysts, tuning of the two-metal ratio is a very important factor for achieving better photocatalytic property …”

Fly‐Ash Cenosphere as Non‐Porous Ag‐Nanoparticle Support for Epoxidation of Styrene

“…[46,47] The absence of extraneous reflexes on the X-ray indicates the presence of high purity sillimanite, which is rare and makes such a cenosphere a valuable demanded raw material. [48,49,50] Minerals of the sillimanite group are quite common, have a relatively high hardness (6-7 points on the Mohs scale), do not dissolve in acids, which is why they are actively used in the metallurgy, ceramics, insulating and chemically resistant materials production, also high purity sillimanite is a raw material for the production of mullite and mullite refractory materials. [51,52] Resulting catalyst was investigated with SEM-microscopy.…”