Gold Nanoparticle Catalysts Research Articles

Efficient formation of propylene oxide under low hydrogen concentration in propylene epoxidation over Au nanoparticles supported on V-doped TS-1

The direct epoxidation of propylene to propylene oxide (PO) represents a unique feature of gold nanoparticle catalysts. Different amounts of vanadium were introduced into TS-1 using a hydrothermal method to give V-TS-1, and the effect of various vanadium loadings on the catalytic performance of Au/V-TS-1 was investigated in the epoxidation of propylene under different reaction conditions. The obtained characterization results indicate that the molecular sieve pore structure and crystalline phase structure of TS-1 were maintained after vanadium incorporation, and vanadium was incorporated into the molecular sieve framework. The introduction of an appropriate amount of vanadium resulted in the homogeneous dispersion of gold particles with a small average particle size, which facilitated the epoxidation reaction. When V was introduced into TS-1, the propylene conversion decreased under the condition of 10 % H2 concentration (C3H6/H2 = 1/1) in the reaction atmosphere, but the PO selectivity was maintained. Interestingly, when the H2 concentration in the reaction atmosphere was lowered to 2 % (C3H6/H2 = 3/1), the propylene conversion in Au/TS-1 was significantly decreased compared to 10 % H2 concentration condition, while in Au/V-TS-1, the propylene conversion was maintained in 2 % H2 concentration condition compared to 10 % H2. Au/V-TS-1 also maintained its selectivity for PO even when the H2 concentration was lowered. Therefore, under low hydrogen concentration conditions, the PO formation rate of Au/V-TS-1 was much higher than that of Au/TS-1. More, the same trend was observed when Mo was added in place of V. Our strategy will guide the design of future catalysts as a way to utilize hydrogen more effectively while maintaining PO productivity.

Ultra-stable and highly reactive colloidal gold nanoparticle catalysts protected using multi-dentate metal oxide nanoclusters

Owing to their remarkable properties, gold nanoparticles are applied in diverse fields, including catalysis, electronics, energy conversion and sensors. However, for catalytic applications of colloidal gold nanoparticles, the trade-off between their reactivity and stability is a significant concern. Here we report a universal approach for preparing stable and reactive colloidal small (~3 nm) gold nanoparticles by using multi-dentate polyoxometalates as protecting agents in non-polar solvents. These nanoparticles exhibit exceptional stability even under conditions of high concentration, long-term storage, heating and addition of bases. Moreover, they display excellent catalytic performance in various oxidation reactions of organic substrates using molecular oxygen as the sole oxidant. Our findings highlight the ability of inorganic multi-dentate ligands with structural stability and robust steric and electronic effects to confer stability and reactivity upon gold nanoparticles. This approach can be extended to prepare metal nanoparticles other than gold, enabling the design of novel nanomaterials with promising applications.

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity.

Exfoliated M-Al layered double hydroxide (M-Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co-Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co-Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co-Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co-Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation.

Dehydrogenative oxidation of hydrosilanes using gold nanoparticle deposited on citric acid-modified fibrillated cellulose: unveiling the role of molecular oxygen.

Efficient and environmentally friendly synthesis of silanols is a crucial issue across the broad fields of academic and industrial chemistry. Herein, we describe the dehydrogenative oxidation of hydrosilane using a gold nanoparticle catalyst supported by fibrillated citric acid-modified cellulose (F-CAC). Au:F-CAC catalysts with various particle sizes (1.7 nm, 4.9 nm, and 7.7 nm) were prepared using the trans-deposition method, a technique previously reported by our group. These catalysts exhibited significant catalytic activity to produce silanols with high turnover frequency (TOF) of up to 7028 h-1. Recycling experiments and transmission electron microscopy (TEM) observation represented the high durability of Au:F-CAC under the reaction conditions, allowing kinetic studies on size dependency. Mechanistic studies were conducted, including isotope labelling experiments, kinetics, and various spectroscopies. Notably, the near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) of the model catalyst (Au:PVP) revealed the formation of catalytically active cationic Au sites on the surface through the adsorption of molecular oxygen, providing a new insight into the reaction mechanism.

Oxidative esterification of 5-hydroxymethylfurfural to dimethyl 2,5-furandicarboxylate over Au-supported poly(ionic liquid)s

Although fossil fuels bring convenience to the production and life of people, they also cause numerous environmental problems. As a result of overexploitation, fossil fuels are gradually being depleted as a nonrenewable resource. Biomass is a green and renewable resource and has attracted people’s attention. As a platform compound derived from renewable biomass, 5-hydroxymethylfurfural (HMF) is important for in-depth research. The oxidative esterification process from HMF to dimethyl furan-2,5-dicarboxylate (FDMC) was achieved using a gold (Au) nanoparticle (NP) catalyst supported on poly(ionic liquid)s (PILs). The comprehensive characterization of the synthesized catalyst showed that the Au NPs were successfully loaded on PILs, and a strong interaction occurred between the catalyst support and the metal. In this work, 10 %Au/PILs-Cl-1 was used as the best catalyst. The conversion of HMF (CHMF) and the selectivity to FDMC (SFDMC) reached 95.08 % and 96.82 %, respectively, under the conditions of 120 °C, 1.5 MPa, 12 h, and 0.5 equiv. CH3ONa. In addition, cycling experiments indicated the stability and successfully recycling of 10 %Au/PILs-Cl-1 catalyst.

Harnessing Supported Gold Nanoparticle as a Single‐Electron Transfer Catalyst for Decarboxylative Cross‐Coupling

AbstractWe found that gold nanoparticles function as single‐electron transfer catalysts to promote decarboxylative cross‐coupling between N‐hydroxy phthalimide esters and disilanes or diborons. A variety of disilanes coupled with alkyl radicals could be generated from N‐hydroxy phthalimide esters via single‐electron reduction by active carbon‐supported gold nanoparticle catalysts to afford diverse alkylsilanes without the need for external bases. Furthermore, the present gold catalytic system was also effective for decarboxylative carbon‐boron coupling to afford alkyl boronates. A detailed mechanistic investigation revealed that single‐electron transfer mediated by supported gold nanoparticles enabled the generation of alkyl radical and silyl radical, thereby enabling radical cross‐coupling. The reusability and environmentally‐friendly nature of supported gold catalyst as well as the scalability of the reaction system enable the practical transformation of carboxylic acid derivatives into value‐added organosilicon and organoboron compounds.

MXene-based gold nanoparticle catalyst with high activity and stability for 4-nitrophenol reduction

Catalytic reduction is considered an effective method for converting organic compounds. However, a lack of efficient catalysts has hindered its practical application. Herein, the cationic poly(diallyldimethylammonium chloride) (PDDA) was used as a stabilizer to synthesize a novel MXene-supported gold nanoparticles composite by electrostatic interaction and self-reduction methods. As a stabilizer bridging transition metal carbides (MXene, Ti3C2Tx) and gold nanoparticles (AuNPs), the PDDA polymer provided rich binding sites for AuNPs immobilization, resulting in uniform distribution of AuNPs on MXene nanosheet and efficient control over their particle size. The synergistic effects of the composite catalyst improved its catalytic activity towards 4-nitrophenol (4-NP) reduction, and the normalized rate constant (K) was high up to 2.65 × 10−2 s−1. Notably, the composite catalyst also showed high stability due to the protection of PDDA, and the conversion efficiency for 4-NP was high up to 94.85% after five recycles. Our findings presented here not only are potential for catalytic applications, but also provide a foundation for the development of efficient MXene-based catalysts.

TbMOF@Au catalytic determination of trace malathion with aptamer SERS/RRS/Abs assay.

Terbium metal-organic framework (TbMOF) was prepared by microwave method with 1,3,5-benzenetricarboxylic acid as ligand. With HAuCl4 as precursor and NaBH4 as reducing agent, TbMOF-loaded gold nanoparticles (AuNPs) catalyst (TbMOF@Au1) was prepared rapidly and characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. It was found that TbMOF@Au1 has a strong catalytic effect on the HAuCl4-Cys nanoreaction, and the produced AuNPs have a strong resonant Rayleigh scattering (RRS) peak and surface plasmon resonance absorption (Abs) peak at 370nm and 550nm, respectively. With the addition of the molecular probe Victoria blue 4R (VB4r), AuNPs have a strong surface-enhanced Raman scattering (SERS) effect, the target analyte molecules are trapped in between the nanoparticles and a hot spot effect created in the process resulting in an extremely high SERS signal. A new SERS/RRS/Abs triple-mode analysis method for Malathion (MAL) was established by coupling this new TbMOF@Au1 catalytic indicator reaction with MAL aptamer (Apt) reaction, and its SERS detection limit was 0.21ng/mL. The SERS quantitative analysis method has been applied to the analysis of fruit samples with the recovery of 92.6-106.6% and the precision of 2.72-8.16%.

Enzymatic and catalytic behaviour of low-dimensional gold nanomaterials in modular nano-composite hydrogels

Inorganic nanoparticles have long been applied as catalysts and nanozymes with exceptional rate constants arising from their large surface areas. While it is understood that high surface area-to-volume ratios and low average atomic coordination are responsible for their exceptional catalytic properties, these facets remain under exploited in the design of gold nanoparticle catalysts and nanozymes. Here we have developed 3D, 2D, and quasi-1D gold nanoparticles for use as catalysts in reducing 4-nitrophenol by sodium borohydride. Each morphology was characterised with transmission electron microscopy and UV–vis absorption spectroscopy, while the highest catalytic activity was achieved when the perimeter-to-surface area, or amount of ‘edge’, was maximised. The particles were then applied as nanozymes in modular nano-composite hydrogels. Independent hydrogel tiles containing either the substrate or catalyst were bonded in stacks, which allowed reagent transport across their interface for the colourimetric detection of hydrogen peroxide. This work presents novel insight into the catalytic activity of low-dimension nanoparticles and their potential application in nanozyme-based diagnostic devices.

Reversible ligand exchange of triphenylphosphine with thiols on gold nanoparticles for Janus modification and catalyst recycling

Separation and regeneration of ultrafine catalysts in reaction system still remain challenging. In this study, we demonstrate a simple route to recycle gold nanoparticle (Au NP) catalysts by alternating surface wettability. Hydrophilic Au NPs protected with 3-mercapto-1,2-propanediol (MPD) were applied to catalyze the reduction of 4-nitrophenol (4-NP) using sodium borohydride as reductant, and were then separated from the suspension by interfacial ligand exchange with a toluene solution containing triphenylphosphine (TPP), led to amphiphilic Janus Au NPs with both MPD and TPP ligands at the toluene-water interface. The catalyst was regenerated by a reversible ligand exchange with a MPD aqueous solution. Experiments show that interfacial ligand exchange between phosphines and thiols on gold surface is reversible, although the forward and backward rates are different. As a result, the Au NP catalyst capped with MPD exhibited an excellent catalytic activity with an apparent rate constant (k) of 2.79 min−1, and the performance could be maintained for more than 10 regeneration cycles. The facile conversion between hydrophilic and amphiphilic Janus Au NPs provides a new pathway to explore monophasic and multiphasic reactions with convenient catalyst separation and regeneration.

Surface Rearrangement and Sublimation Kinetics of Supported Gold Nanoparticle Catalysts

Heterogeneous catalysts consisting of supported metallic nanoparticles typically derive exceptional catalytic activity from their large proportion of undercoordinated surface sites which promote adsorption of reactant molecules. Simultaneously, these high energy surface configurations are unstable, leading to nanoparticle growth or degradation and eventually a loss of catalytic activity. Surface morphology of catalytic nanoparticles is paramount to catalytic activity, selectivity, and degradation rates, however it is well-known that harsh reaction conditions can cause the surface structure to change. Still, limited research has focused on understanding the link between nanoparticle surface facets and degradation rates or mechanisms. Here, we study a model Au supported catalyst system over a range of temperatures using a combination of in situ transmission electron microscopy, kinetic Monte Carlo simulations, and density functional theory calculations to establish an atomistic picture of how variations in surface structures and atomic coordination environments lead to shifting evolution mechanisms as a function of temperature. By combining experimental results, which yield direct observation of dynamic shape changes and particle sublimation rates, with computational techniques, which enable understanding the fundamental thermodynamics and kinetics of nanoparticle evolution, we illustrate a two-step evolution mechanism in which mobile adatoms form through desorption from low-coordination facets and subsequently sublimate off the particle surface. By understanding the role of temperature in the competition between surface diffusion and sublimation, we are able to show how individual atomic movements lead to particle scale morphological changes and rationalize why sublimation rates vary between particles in a system of nearly identical nanoparticles.

Facile preparation of highly active zirconia-supported gold nanoparticle catalyst

Au/insulating ZrO2 prepared by a modified deposition precipitation (DP) method with a pre-step of long-time stirring of ZrO2 NPs in HAuCl4 solution shows catalytic activity for two electron-oxygen reduction much higher than Au/semiconducting metal oxides prepared by the normal DP method.

Ultrasound-assisted synthesis of gold nanoparticles supported on β-cyclodextrin for catalytic reduction of nitrophenols

Nitrophenols with high toxicity are well known as one of the main pollutants in water environment while aminophenols, products of the reduction, are important intermediates in the fabrication of several drugs. Thus, the reduction of nitrophenols is considerably attractive in wastewater treatment and pharmaceutical fields. In this work, gold nanoparticles (AuNPs) catalyst was straightforwardly fabricated using β-cyclodextrin as a reducing and stabilizing agent under ultrasound irradiation. The synthetic conditions were explored via the changes in concentration of β-cyclodextrin, environmental pH, temperature and time. The synthesized AuNPs under the optimal condition showed a size distribution in range of 3–21 nm with a mean size of 12 nm. The dynamic lighting scatter and zeta potential data showed the stable colloidal solutions and X-ray diffraction and selected area electron diffraction patterns confirmed crystalline structure of AuNPs. The influence of reagents and the nanoparticles on kinetic data of the reduction was investigated. The kinetic data showed that the performance of 2-nitrophenol reduction is better than that of 4-nitrophenol while rate constants of the reduction is linear to both initial concentrations of nitrophenol substrates and catalyst amount.

Silk Bionanocomposites for Organic Dye Absorption and Degradation

Organic dyes are extensively used in the textile, paper and paint industries, among others. However, the lack of efficient treatment of disposals leads to the release of these toxic molecules into the environment, which has an enormous impact on living organisms. Dye absorption is the most common approach used to tackle this problem. However, the ideal solution should include dye degradation and absorbent regeneration, reducing the environmental impact of the procedure. Dye degradation can be achieved by catalysis. Recently, silk fibroin (SF) has been shown to have incredible absorbent properties. Herein, we characterized the capacity of SF hydrogels to absorb methylene blue (MB), an extensively used cationic organic dye. Moreover, the effect of a pretreatment of the SF hydrogel at different pH and ionic environments is also studied. Interestingly, opposite behaviors are observed when absorbing MB or brilliant blue (an anionic dye), suggesting an electrostatic-based interaction. Furthermore, the regeneration of a MB-saturated SF hydrogel by immersion in acidic pH and its further reuse were evaluated. Finally, the SF hydrogel was coupled with a gold nanoparticle catalyst, which resulted in a material able to absorb and catalyze the MB reduction by sodium borohydride in situ, leading to dye degradation. Overall, this work presents a biodegradable reusable material able to absorb and reduce MB in aqueous media.

Back Cover: Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates (Angew. Chem. Int. Ed. 34/2022)

Supported gold nanoparticle catalysts have attracted growing interest in aerobic oxidation reactions. In their Research Article (e202205873), Kazuya Yamaguchi, Kosuke Suzuki et al. describe a method for the design of supported anionic gold nanoparticle catalysts using negatively charged multivacant polyoxometalates. The electronic states of the catalysts can be sequentially modulated, and the catalyst prepared using [SiW9O34]10− acted as a reusable heterogeneous catalyst, showing superior catalytic activity and enhanced stability compared to conventional catalysts.

Rücktitelbild: Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates (Angew. Chem. 34/2022)

Goldnanopartikel-Katalysatoren sind von großem Interesse für aerobe Oxidationsreaktionen. In ihrem Forschungsartikel (e202205873) beschreiben Kazuya Yamaguchi, Kosuke Suzuki et al. eine Methode für die Entwicklung von Katalysatoren aus anionischen Goldnanopartikeln mithilfe von negativ geladenen, mehrwertigen Polyoxometallaten. Die elektronischen Zustände der Katalysatoren können moduliert werden, und der unter Verwendung von [SiW9O34]10− hergestellte Katalysator fungierte als wiederverwendbarer heterogener Katalysator mit überlegener katalytischer Aktivität und verbesserter Stabilität im Vergleich zu herkömmlichen Katalysatoren.

Ultrafine gold nanoparticles dispersed in conjugated microporous polymers with sulfhydryl functional groups to improve the reducing activity of 4-nitrophenol

Achieving the preparation of uniformly loaded ultrafine metal nanoparticles catalysts is a key problem in the field of catalysis. In this study, ultrafine gold nanoparticle catalysts were prepared by using conjugated microporous polymers (CMPs) modified with sulfhydryl group to support gold. High-resolution transmission electron microscopy (HR-TEM) at Au@TBD-S-SH showed that the average particle size of gold nanoparticles (Au NPs) was 3.4 nm. The higher catalytic activity was shown by comparing the normalized reaction rate constants (Knor = 117) from the work of other investigators. Moreover, the catalysts maintained their activity after ten cycles. Meanwhile, Au NPs increased in size probably on account of adsorption products and slight agglomeration. These studies demonstrated that functionalized CMPs loaded with noble metals can efficiently remove phenolic compounds from wastewater.

Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates

AbstractAlthough supported anionic gold nanoparticle catalysts have been theoretically investigated for their efficacy in activating O2 in aerobic oxidation reactions, limited studies have been reported due to the difficulty of designing these catalysts. Herein, we developed a feasible method for preparing supported anionic gold nanoparticle catalysts using multivacant lacunary polyoxometalates with high negative charges. We confirmed the strong and robust electronic interaction between gold nanoparticles and multivacant lacunary polyoxometalates, and the electronic states of the supported gold nanoparticle catalysts can be sequentially modulated. Particularly, the catalyst prepared using [SiW9O34]10− acted as an efficient reusable heterogeneous catalyst, showing superior catalytic performance for the oxidative dehydrogenation of piperidone derivatives to the corresponding enaminones and remarkably higher stability than supported gold nanoparticle catalysts without this modification.

Supported Anionic Gold Nanoparticle Catalysts Modified Using Highly Negatively Charged Multivacant Polyoxometalates.

Although supported anionic gold nanoparticle catalysts have been theoretically investigated for their efficacy in activating O2 in aerobic oxidation reactions, limited studies have been reported due to the difficulty of designing these catalysts. Herein, we developed a feasible method for preparing supported anionic gold nanoparticle catalysts using multivacant lacunary polyoxometalates with high negative charges. We confirmed the strong and robust electronic interaction between gold nanoparticles and multivacant lacunary polyoxometalates, and the electronic states of the supported gold nanoparticle catalysts can be sequentially modulated. Particularly, the catalyst prepared using [SiW9 O34 ]10- acted as an efficient reusable heterogeneous catalyst, showing superior catalytic performance for the oxidative dehydrogenation of piperidone derivatives to the corresponding enaminones and remarkably higher stability than supported gold nanoparticle catalysts without this modification.

Reversible ionic liquids (RevILs) for the preparation of thermally stable SBA-15 supported gold nanoparticle catalysts

Reversible ionic liquids (RevILs) are ionic liquids that can be switched between molecular and ionic forms via two stimuli, and they can assist in the synthesis of colloidal gold nanoparticles. The RevIL-stabilized gold nanoparticles are deposited in the pores of SBA-15 mesoporous silica via incipient wetness without the functionalization of the SBA-15 surface. The location of nanoparticles inside the pores was confirmed by transmission electron microscopy technique and by a measured increase in the thermal stability of the nanoparticles in SBA-15 compared to non-porous silica. The porous gold catalysts are active in the selective oxidation of benzyl alcohol without calcination due to the absence of the ligands on the gold surface after deposition. Additionally, they are more active than the non-porous gold catalysts, indicating that the pore geometry enhances catalytic performance. Ultimately, the catalysts prepared by RevIL technique are thermally stable and active and show fine control over particle size.