Continuous microfluidic synthesis of colloidal ultrasmall gold nanoparticles:<i>in situ</i>study of the early reaction stages and application for catalysis

Tofighi, Ghazal; Lichtenberg, Henning; Pesek, Jan; Sheppard, Thomas L.; Wu, Wei; Schöttner, Ludger; Rinke, Günter; Dittmeyer, Roland; Grunwaldt, Jan‐Dierk

doi:10.1039/c7re00114b

Cited by 44 publications

(66 citation statements)

References 49 publications

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“…The spectra showed very weak surface plasmon resonance (SPR) bands, indicating that the particle size of the Au nanoparticles is smaller than ≈3 nm. According to literature [38,45,46], below this value the SPR is strongly suppressed and surface scattering is the factor dominating the UV-Vis spectrum. The colloid with the expected larger size presents additionally a faint band centered at about 525 nm, indicating the possible presence of particles of up to 20 nm size.…”

Section: Catalyst Characterizationmentioning

confidence: 94%

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

et al. 2020

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For the production of chemicals from biomass, new selective processes are required. The selective oxidation of 5-(Hydroxymethyl)furfural (HMF), a promising platform molecule in fine chemistry, to 2,5-furandicarboxylic acid (FDCA) is considered a promising approach and requires the oxidation of two functional groups. In this study, Au/ZrO 2 catalysts with different mean particle sizes were prepared by a chemical reduction method using tetrakis(hydroxymethyl)phosphonium chloride (THPC) and tested in HMF oxidation. The catalyst with the smallest mean particle size (2.1 nm) and the narrowest particle size distribution was highly active in the oxidation of the aldehyde moiety of HMF, but less active in alcohol oxidation. On the other hand, increased activity in FDCA synthesis up to 92% yield was observed over catalysts with a larger mean particle size (2.7 nm), which had a large fraction of small and some larger particles. A decreasing FDCA yield over the catalyst with the largest mean particle size (2.9 nm) indicates that the oxidation of both functional groups require different particle sizes and hint at the presence of an optimal particle size for both oxidation steps. The activity of Au particles seems to be influenced by surface steps and H bonding strength, the latter particularly in aldehyde oxidation. Therefore, the presence of both small and some larger Au particles seem to give catalysts with the highest catalytic activity.Catalysts 2020, 10, 342 2 of 13 oxidation of HMF has gained great interest in recent years. Selective oxidation of HMF can for example give 5-hydroxymethyl-2-furancarboxylic acid (HFCA) or 2,5-diformylfuran. One of the most important oxidation products is 2,5-furandicarboxylic acid (FDCA), [11,12] which is produced via the oxidation of both functional groups of HMF (Scheme 1). The structural similarity of FDCA to terephthalic acid led to its consideration as one of the twelve important molecules that can be produced from sugar-containing biomass feedstock [11,12]. Therefore, FDCA may be used in future bio-based polymers thus overcoming the need of petrochemical-based terephthalic acid [13,14]. Synthetic approaches for FDCA synthesis include stoichiometric oxidation reactions [15] as well as catalytic routes with mostly molecular oxygen. The latter range from bio-[16,17] to electro-[18-20] and metal catalysis. Current FDCA production is based on the homogeneously catalyzed AMOCO process, which is carried out in acetic acid solvent at 125 • C and 70 bar air in the presence of a Cu/Mn/Br catalyst [21]. In addition, heterogeneous metal catalysts have been applied in HMF oxidation. Especially supported noble metals like Pt [22][23][24] or Pd [25][26][27] are catalytically active in this reaction. Among others, supported gold-based catalysts show high activity in the oxidation of HMF with oxygen to FDCA [28][29][30][31][32][33][34][35]. For example, Au supported on CeO 2 nanoparticles allowed the production of FDCA in 96% yield after 5 h at 130 • C [28].Catalysts 2020, 10, x FOR PEER REVIEW 2 of...

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Section: Catalyst Characterizationmentioning

confidence: 94%

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

et al. 2020

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“…This dates back to 1973 where Au NPs were synthesized and evaluated as a useful catalyst for olefin hydrogenation . In 2017, Grunwaldt and co‐workers engineered a continuous microfluidic setup that reduced HAuCl 4 with sodium borohydride (NaBH 4 ) in the presence of PVP to synthesize ultrasmall Au NPs with catalytic applications in mind . Specifically, the setup used pressurized vessels that allowed pulsation‐free flow of reactants in a microfluidic chip with integrated mixers.…”

Section: Case Studiesmentioning

confidence: 99%

Continuous Flow Routes toward Designer Metal Nanocatalysts

Santana

Skrabalak

2019

Advanced Energy Materials

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Mono‐ and multimetallic nanoparticles (NPs) have diverse and tunable physicochemical properties that arise from their compositions as well as crystallite size and shape. The ability to control precisely the composition and structure of NPs through synthesis is central to achieving state‐of‐the‐art designer metal NPs for use as catalysts and electrocatalysts. However, a major limitation to the use of designer metal NPs as catalysts is the ability to scale their syntheses while maintaining structural precision. To address this challenge, continuous flow routes to metal NPs involving the use of droplet microreactors are being developed, providing the synthetic versatility necessary to achieve known and completely new nanostructures. This progress report outlines how the chemistry and process parameters of droplet microreactors can be used to achieve high performing nanocatalysts through control of NP composition, size, shape, and architecture and outlines directions toward previously unimaginable nanostructures.

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“…Homogeneous synthesis. Homogeneous synthesis consists of simple mixing of reagents and surfactants using usually 2 or 3 inlets which combine into a single channel, 15,26 altogether forming a Y or T shape depending on the angle of contact between the channels, see Fig. 1a.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, sometimes mixers are used to enhance the mixing and to provide better control of the metal NP size distribution and composition. These mixers use the inertia of the fluid to merge the reagents in a more vigorous manner 26,31,32 reducing the time of mixing to a few ms. 26 On the other hand, Fu et al used the slow diffusion in homogeneous synthesis as an advantage to slow down the process and identify intermediate shapes formed during the synthesis of NPs. Typically, the synthesis is performed at room temperature, however higher temperatures are also used which can be very well controlled when integrated in the microfluidic chips.…”

Section: Introductionmentioning

confidence: 99%

Microfluidics and catalyst particles

et al. 2019

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In this review article, we discuss the latest advances and future perspectives of microfluidics for micro/ nanoscale catalyst particle synthesis and analysis. In the first section, we present an overview of the different methods to synthesize catalysts making use of microfluidics and in the second section, we critically review catalyst particle characterization using microfluidics. The strengths and challenges of these approaches are highlighted with various showcases selected from the recent literature. In the third section, we give our opinion on the future perspectives of the combination of catalytic nanostructures and microfluidics. We anticipate that in the synthesis and analysis of individual catalyst particles, generation of higher throughput and better understanding of transport inside individual porous catalyst particles are some of the most important benefits of microfluidics for catalyst research. SynthesisThis section focuses on the most recent approaches within the last 8 years. For a more extensive overview of the synthesis of nanostructures focused on the processes taking place inside the microfluidic systems, 5 the final application 4 or the microfluidic technology used 6,7 we refer the reader to other review articles. Metal nanoparticlesMetal nanoparticles exhibit very interesting catalytic, optical, chemical, electromagnetic and magnetic properties, all of them depending to a large degree on their size and composition. Regarding catalysis, a decrease of the NP size leads to a surface-area increase per mass, providing more active sites. Also, the surface structure is of vital importance for the NP selectivity: the presence of steps, edges or terraces in the atomic surface can influence the reaction pathways to Lab Chip, 2019, 19, 3575-3601 | 3575 This journal is

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Continuous microfluidic synthesis of colloidal ultrasmall gold nanoparticles:in situstudy of the early reaction stages and application for catalysis

Abstract: The formation of gold nanoparticles in the first 2–20 ms of the reaction was studiedin situwith XAS using microfluidics.

Cited by 44 publications

References 49 publications

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

Continuous Flow Routes toward Designer Metal Nanocatalysts

Microfluidics and catalyst particles

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