Development of Ultrafine Multichannel Microfluidic Mixer for Synthesis of Bimetallic Nanoclusters: Catalytic Application of Highly Monodisperse AuPd Nanoclusters Stabilized by Poly(N-vinylpyrrolidone)

Abstract

On account of their novel properties, bimetallic nanoparticles and nanoclusters (NCs) are strong potential candidates for optical, magnetic, and catalytic functional materials. These properties depend on the chemical composition and size (number of constituent atoms) of the NCs. Control of size, structure, and composition is particularly important for fabricating highly functional materials based on bimetallic NCs. Size- and structure-controlled synthesis of two-element alloys can reveal their intrinsic electronic synergistic effects. However, because synergistic enhancement of activity is strongly affected by composition as well as by size and structure, controlled synthesis is a challenging task, particularly in catalytic applications. To investigate catalytic synergistic effects, we have synthesized highly monodisperse, sub-2 nm, solid-solution AuPd NCs stabilized with poly(N-vinylpyrrolidone) (AuPd:PVP) using a newly developed ultrafine microfluidic mixing device with 15 μm wide multiple lamination channels. The synergistic enhancement for catalytic aerobic oxidation of benzyl alcohol exhibited a volcano-shaped trend, with a maximum at 20-65 at. % Pd. From X-ray photoelectron spectroscopic measurements, we confirmed that the enhanced activity originates from the enhanced electron density at the Au sites, donated by Pd sites.

Chemical Nature of Microfluidically Synthesized AuPd Nanoalloys Supported on TiO2

“…Monometallic Au and Pd NPs as well as AuPd nanoalloys were synthesized following a previously published procedure [40][41] . In this colloidal route, the metal precursors are reduced under basic conditions (via NaBH4) in the presence of PVP as a surfactant.…”

“…homogeneous nanoalloys, core-(multi)-shell and segregated subcluster structures), and achieving narrow size distributions of the nanoalloys, a requirement for further tuning the desired catalytic properties. [38][39][40] Recently, we have studied the synthesis of Au and Pd NPs and also homogeneous AuxPdy nanoalloys inside a novel microfluidic reactor 41 . For the present study (note that this work was conducted in the frame of the PhD thesis by Ghazal Tofighi 42 ), such bimetallic NPs were deposited on TiO2, and the effects of alloying and Au-Pd interaction on surface properties.…”

Microfluidically synthesized Au, Pd and AuPd nanoparticles supported on SnO2 for gas sensing applications

“…The colloidal route for synthesis of ultrasmall Au, Pd and AuPd NPs using a microfluidic reactor was adopted from our previous reports [30,31] and Hayashi et. al [32]. An aqueous solution of metal precursors (7.5 mM) with 666 mg PVP was prepared for all samples with nominal molar Au:Pd ratios of 1:0, 1:1 and 0:1.…”

Compositional Effect in AuPd Bimetallic Nanoparticles Towards Product Selectivity during Aerobic Oxidation of α-Hydroxy Esters and Phosphonates

“…The results confirmed the formation of bimetallic nanoalloys as the disappearance of the SPR characteristics could be attributed to changes in the band structure of Au NPs on alloying with Pd . The XRD patterns of Au, Pd and bimetallic AuPd NPs (Figure b) exhibited two major diffraction peaks in the region 30° < 2θ < 70° that correspond to the (111) and (200) of the fcc structure of monometallic Au and Pd . The diffraction peaks of the bimetallic AuPd NPs were observed in between the diffraction peaks of pure Au and Pd NPs, signifying the formation of AuPd alloys.…”