Monometallic Au Research Articles

State of the art on plasma-liquid route synthesis monometallic Au, bimetallic Au/Ag core–shell and alloy nanoparticles: Toxicological, сanalytical, antimicrobial activity for environmental control

Nanoparticles (Au monometallic, bimetallic structures Au-Ag alloy and Aucore – Agshell) were synthesized in aqueous solutions with traditional capping agent - sodium citrate, using a one-step (for monometalic and alloy structure) and two–step (for Aucore – Agshell NPs) liquid-phase anode type plasma process. The effects of parameters of synthesis: precursors concentration, the solution plasma process discharge time, molar contents Ag+/Au3+ for alloy NPs, and molar content of Ag+ for Au core NP to the characteristics of the synthesized NPs, including average size (the size distribution, polydispersity index), optical absorption properties ect.) were investigated. The synthesized nanoparticles have the following characteristics: Au NPs with λ=530–540 nm and d = 5–60 nm, the monometalic structure; Ag/Au with the λ=410–530 nm and d = 28–80 nm, bimatalic strucrure of alloy; NPs with significant blue-shift the λ=530→410 nm, depending the shell thickness (the thickness of the deposited Ag shells varied from ∼1–15 nm) and d = 21–35 nm for NPs core(Au)–shell(Ag). TEM images clearly confirm the effectiveness of a one- and two-step plasma-liquid treatment for the synthesis of monometallic Au NPs and the two different structures of the NPs (bimetallic structures Au-Ag alloy and Aucore@– Agshell). The effect of nanoparticle structure on antimicrobial and catalytic properties relative to their respective monometallic counterparts was demonstrated. Among the different investigated structure NPs only for bimetallic core−shell structured AucoreAgshell NPs was found strong synergistic effect for antimicrobial and catalytical activity.

Impact of Surface Composition Changes on the CO2-Reduction Performance of Au-Cu Aerogels.

Over the past decades, the electrochemical CO2-reduction reaction (CO2RR) has emerged as a promising option for facilitating intermittent energy storage while generating industrial raw materials of economic relevance such as CO. Recent studies have reported that Au-Cu bimetallic nanocatalysts feature a superior CO2-to-CO conversion as compared with the monometallic components, thus improving the noble metal utilization. Under this premise and with the added advantage of a suppressed H2-evolution reaction due to absence of a carbon support, herein, we employ bimetallic Au3Cu and AuCu aerogels (with a web thickness ≈7 nm) as CO2-reduction electrocatalysts in 0.5 M KHCO3 and compare their performance with that of a monometallic Au aerogel. We supplement this by investigating how the CO2RR-performance of these materials is affected by their surface composition, which we modified by systematically dissolving a part of their Cu-content using cyclic voltammetry (CV). To this end, the effect of this CV-driven composition change on the electrochemical surface area is quantified via Pb underpotential deposition, and the local structural and compositional changes are visually assessed by employing identical-location transmission electron microscopy and energy-dispersive X-ray analyses. When compared to the pristine aerogels, the CV-treated samples displayed superior CO Faradaic efficiencies (≈68 vs ≈92% for Au3Cu and ≈34 vs ≈87% for AuCu) and CO partial currents, with the AuCu aerogel outperforming the Au3Cu and Au counterparts in terms of Au-mass normalized CO currents among the CV-treated samples.

Boosting Solvent-Free Aerobic Oxidation of Benzylic Compounds into Ketones over Au-Pd Nanoparticles Supported by Porous Carbon

The exploitation of highly efficient solvent-free catalytic systems for the selective aerobic oxidation of benzylic compounds to produce corresponding ketones with molecular oxygen under mild conditions remains a great challenge in the chemical industry. In this work, Au-Pd nanoparticles supported on porous carbon catalysts were fabricated by the borax-mediated hydrothermal carbonization method and the chemical reduction method. The physicochemical properties of Au-Pd bimetallic samples were examined by XRD, N2 sorption, SEM, TEM, and XPS techniques. The Au-Pd nanoparticles have successfully immobilized on the spherical carbon support with a porous structure and large surface area. A solvent-free catalytic oxidation system was constructed to selectively convert indane into indanone with Au-Pd nanocatalysts and O2. In contrast with a monometallic Au or Pd catalyst, the resulting bimetallic Au-Pd catalyst could effectively activate O2 and exhibit improved catalytic activity in the controlled oxidation of indane into indanone under 1 bar O2. A total of 78% conversion and >99% selectivity toward indanone can be achieved under optimized conditions. The synergistic effect of Au and Pd and porous carbon support contributed to the high catalytic activity for aerobic benzylic compound oxidation. This work offers a promising application prospect of efficient and recyclable Au-Pd nanocatalysts in functional benzylic ketone production.

Au-Pt heterostructure cocatalysts on g-C3N4 for enhanced H2 evolution from photocatalytic glucose reforming

Glucose from plants or food industry wastes is a cost-effective hole scavenger for photocatalytic water splitting, but the related H2 evolution rate is always restricted by the fast recombination of photo electron-hole pairs and the poor intrinsic activity of traditional Pt cocatalysts. Herein, we fabricated Au-Pt heterostructure cocatalyst that consist of one ∼3 nm Au core and several ∼1 nm Pt islands on ultrathin g-C3N4 through one-pot photo-deposition. The heterostructure exhibited superior H2 evolution activity to monometallic Au or Pt nanoparticles. Our experiments and theoretical calculations demonstrated that the enhanced activity was caused by the synergistic effect between Au and Pt, rather than the well-known plasmonic effect of Au. The heterostructure not only favored the trapping of photo electrons from g-C3N4, but also had suitable adsorption strength of H*, exhibiting high intrinsic activity towards H2 evolution. Our research provides a strategy to boost photocatalytic H2 evolution by regulating the synergy of bimetallic cocatalysts.

Electrogenerated chemiluminescence imaging of plasmon-induced electrochemical reactions at single nanocatalysts.

This study explores plasmon-induced electrochemical reactions on single nanoparticles using electrogenerated chemiluminescence microscopy (ECLM). Under laser irradiation, real-time screening showed lower plasmon-induced reaction efficiency for bimetallic Au@Pt nanoparticles compared to monometallic Au nanoparticles. ECLM offers a high-throughput imaging and precise quantitative approach for analyzing photo-electrochemical conversion at single nanoparticle level, valuable for both theoretical exploration and optimization of plasmonic nanocatalysts.

Study of CuSb bimetallic flow-through gas diffusion electrodes for efficient electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (eCO2R) to industrially important feedstock has received great attention, but it faces different challenges. Among them, the poor CO2 mass transport due to low intrinsic CO2 solubility significantly limits the rate of reduction reactions, leading to lower catalytic performance; thereby, commercially relevant current densities can’t be achieved. Moreover, the poor activity and selectivity of high-cost monometallic catalysts, including Cu, Zn, Ag, and Au, undermine the efficiency of eCO2R. Flow-through gas diffusion electrodes (FTGDE), a newly developed class of GDEs, can potentially solve the issue of poor CO2 mass transport because they directly feed the CO2 to the catalyst layer. In addition, abundant surface area, porous structure, and improved triple-phase interface make them an excellent candidate for extremely high rate eCO2R. Antimony, a low-cost and abundant metalloid, can be effectively tuned with Cu to produce useful products such as CO, formate, and C2H4 through eCO2R. Herein, a series of porous binary CuSb FTGDEs with different Sb compositions are fabricated for the electrocatalytic reduction of CO2 to CO. The results show that the catalytic performance of CuSb FTGDEs improved with increasing Sb content up to a certain threshold, beyond which it started to decrease. The CuSb FTGDE with 5.4 g of antimony demonstrated higher current density (206.4 mA/cm2) and faradaic efficiency (72.82 %) at relatively lower overpotentials. Compared to gas diffusion configuration, the poor catalytic activity and selectivity achieved by CuSb FTGDE in non-gas diffusion configuration signifies the importance of improved local CO2 concentration and improved triple-phase interface formation in GDE configuration. The several hours stable operation of CuSb FTGDEs during eCO2R demonstrates its potential for efficient electrocatalytic conversion applications.

Facile and Low-Cost Fabrication of SiO2-Covered Au Nanoislands for Combined Plasmonic Enhanced Fluorescence Microscopy and SERS.

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Detection and characterization of mono- and bimetallic nanoparticles produced by electrical discharge plasma generators using laser-induced breakdown spectroscopy

This work investigates the performance of laser induced breakdown spectroscopy (LIBS) for the detection and characterization of nanoparticles generated by spark discharge generators (SDG) and arc discharge generators (ADG). LIBS nanoaerosol analysis was carried out according to both on-line (in a gas stream) and off-line (after collection on a filter) methodologies for monometallic (Cu and Au) and bimetallic (AgCo, SnCu, AgAu) nanoparticles generated by ADG and SDG. It was shown that LIBS is not only capable of detecting the presence of nanoparticles in real time, but LIBS spectra can also be used to provide qualitative and quantitative compositional information, as well as estimates for the particle number concentration. This analytical capability, combined with the compact and robust character of LIBS instrumentation, can be put to use for the real-time monitoring of industrial gas-phase nanoparticle synthesis or environmental or workplace exposure to nanoparticles.

A novel bimetallic (Au-Pd)-decorated reduced graphene oxide nanocomposite enhanced Rhodamine B photocatalytic degradation under solar irradiation

Nowadays, water quality is one of the main challenges facing humanity. Recently, hybrid nanomaterials have attracted great attention because they can treat water solutions. In this study, Sol-Immobilization synthesized monometallic (Pd and Au) and bimetallic (Pd-Au) hybrid nanomaterials supported on reduced graphene oxide (rGO) were synthesized as catalysts for the photocatalytic Rhodamine B degradation under direct sunlight. The as-synthesized nanomaterials were characterized using XRD, Raman spectroscopy, UV-DRS spectrophotometer, HR-TEM techniques, and X-ray Photoelectron Spectroscopy. The catalytic activities of Pd/rGO and Au/rGO were compared with those of Aux-Pdy/rGO, and a higher photocatalytic degradation efficiency was found for the bimetallic-supported rGO sample. At optimum conditions, Au0.75-Pd0.25/rGO achieved the best dye degradation efficiency of 98%. The reusability study results showed that Au0.75-Pd0.25/rGO retained 89% of its initial activity after five successive uses. The scavenging study results proved that hydroxyl radicals are the major reactive species in the photocatalytic degradation reaction. These findings indicate that Au0.75-Pd0.25/rGO catalyst is a promising material for the treatment of water contaminated with organic dyes under sunlight.

Bimetallic AuCo supported on magnetic crosslinked copoly(ionic liquid) nanohydrogel and study of its catalytic activity

Synergistic effects in bimetallic catalysts produce a catalyst with superior activity than a monometallic component. In this work, a novel magnetic crosslinked copoly(ionic liquid) nanohydrogel was synthesized and employed for the stabilization of AuCo bimetallic nanoparticles (Fe3O4@PolyIL‐AuCo). This material was characterized using different instrumental techniques such as FT‐IR, TGA, XPS, VSM, solid‐state UV–Vis, SEM mapping, and TEM. Results indicated a narrow size distribution of nanoparticles and high water dispersibility of Fe3O4@PolyIL‐AuCo. Using this catalyst, a series of nitroarenes were reduced to the corresponding amines in aqueous media. In addition, organic dyes were efficiently degraded by this catalyst. Different experiments dealing with the same transformation confirmed that Fe3O4@PolyIL‐AuCo exhibited higher catalytic activity than the similar monometallic Au and Co catalysts. This catalyst was recycled for at least 11 consecutive runs with very small deactivation, and TEM, VSM, and XPS confirmed the stability of the reused catalyst.

Voltammetric studies on the interaction of ds-DNA with anti-cancer agents imatinib and erlotinib – Comparison of Au and Pt nanoparticle effects to drug-DNA complex formation

The interactions of imatinib (IMA) and erlotinib (ERL) with calf-thymus double-stranded deoxyribonucleic acid (ds-DNA) were studied by using monometallic (Au and Pt) and bimetallic (Au + Pt) nanoparticles modified DNA biosensors. The prepared electrochemical biosensors were designed to show the interaction between IMA (or ERL) and ds-DNA. The characterization of the prepared sensors was carried out by energy-dispersive X-ray spectroscopy (EDX). The influence of Au, Pt, and Au + Pt nanoparticles in the modified biosensor was investigated to elucidate the interaction between the anti-cancer drugs and ds-DNA. The interaction was realized based on the electrochemical oxidation signal (at about +0.80 V) of the guanine (dGu) base of ds-DNA by differential pulse voltammetry (DPV) in pH 4.8 acetate buffer. The effect of the nanoparticle’s concentration and interaction time of IMA (and ERL) with ds-DNA on the electrochemical response of dGu were optimized. The results showed that Au + Pt nanoparticles, especially for IMA, significantly affected the binding constant value of the drugs to ds-DNA. Interaction studies have also shown that the binding mode for IMA and ERL could be intercalation and groove binding and the binding constant values were found to be 68.3 × 106 M−1 and 27.3 × 107 M−1, respectively.

Oxide-supported metal catalysts for anaerobic NAD+ regeneration with concurrent hydrogen production

We report SiO2-supported monometallic Pt, Pd, Au, Ni, Cu and Co catalysts for proton-driven NAD+ regeneration, co-producing H2. All metals are fully selective to NAD+ where the order of turnover frequencies (Pt > Pd > Cu > Au, Ni and Co) coincides with those otherwise observed in electrochemical hydrogen evolution reactions. This has revealed that NADH is capable of converting the metal sites into a “cathode” without an external potential and the NADH to NAD+ reaction involves transferring electron and hydrogen atom separately. Electron-deficient Ptδ+ (on CeO2) enhances TOF and the heterogeneous Pt/CeO2 catalyst is recyclable without losing any activity/selectivity.

Unique Electron-Transfer-Mediated Electrochemiluminescence of AuPt Bimetallic Nanoclusters and the Application in Cancer Immunoassay.

Noble Metal nanoclusters (NCs) are promising electrochemiluminescence (ECL) emitters due to their amazing optical properties and excellent biocompatibility. They have been widely used in the detection of ions, pollutant molecules, biomolecules, etc. Herein, we found that glutathione-capped AuPt bimetallic NCs (GSH-AuPt NCs) emitted strong anodic ECL signals with triethylamine as co-reactants which had no fluorescence (FL) response. Due to the synergistic effect of bimetallic structures, the ECL signals of AuPt NCs were 6.8 and 94 times higher than those of monometallic Au and Pt NCs, respectively. The electric and optical properties of GSH-AuPt NCs differed from those of Au and Pt NCs completely. An electron-transfer mediated ECL mechanism was proposed. The excited electrons may be neutralized by Pt(II) in GSH-Pt and GSH-AuPt NCs, resulting in the vanished FL. Furthermore, abundant TEA radicals formed on the anode contributed electrons to the highest unoccupied molecular orbital of GSH-Au2.5Pt NCs and Pt(II), booming intense ECL signals. Because of the ligand effect and ensemble effect, bimetallic AuPt NCs exhibited much stronger ECL than GSH-Au NCs. A sandwich-type immunoassay for alpha fetoprotein (AFP) cancer biomarkers was fabricated with GSH-AuPt NCs as signal tags, which displayed a wide linear range from 0.01 to 1000 ng·mL-1 and a limit of detection (LOD) down to 1.0 pg·mL-1 at 3S/N. Compared to previous ECL AFP immunoassays, this method not only had a wider linear range but also a lower LOD. The recoveries of AFP in human serum were around 108%, providing a wonderful strategy for fast, sensitive, and accurate cancer diagnosis.

Boosting the Catalytic Performance of AuAg Alloyed Nanoparticles Grafted on MoS2 Nanoflowers through NIR-Induced Light-to-Thermal Energy Conversion.

MoS2 nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS2 NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0-2.5 nm) was possible through the decomposition of organometallic complexes [Au2Ag2(C6F5)4(OEt2)2]n and [Au(C6F5)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1-4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS2 NFs component. The AuAg-MoS2 nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS2 nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field-Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy.

The Activity of Vossia cuspidata Polysaccharides-Derived Monometallic CuO, Ag, Au, and Trimetallic CuO-Ag-Au Nanoparticles Against Cancer, Inflammation, and Wound Healing

The biosynthesis of metal nanoparticles using plant extracts is an eco-friendly and inexpensive solution that has strong potential and applications in science and industry. This study aims to synthesize Cu, Ag, and Au monometallic and trimetallic nanoparticles (NPs) using the extracted polysaccharides (PS) of Vossia cuspidata (Roxb.) Griff. leaves. Besides, the anti-cancer, anti-inflammatory, and wound healing potentials of the synthesized NPs were tested. The synthesized NPs were characterized using standard technological methods. We succeeded in green synthesizing CuO, Ag, Au, monometallic, and CuO-Ag-Au trimetallic NPs. The synthesized NPs had weak cytotoxicity at low concentrations (6.5 µg/ml), but the viability of cancer cells was reduced by increasing the concentration, suggesting that the synthesized NPs have potent anti-cancer properties against the cells. The synthesized NPs had 19.44–45.9 μg/ml cytotoxic activity (IC50) against the MCF-7 cell line, 16.50–51.92 μg/ml against A549, and 115.90–165.9 μg/ml for normal lung cells (WI-38). TMNPs were the most effective cytotoxic agents against all the tested cell lines, followed by AuNPs on MCF-7 and CuONPs on A549. The cotton fabric-treated TMNPs and CuONPs exhibited anti-inflammatory properties greater than fabric-treated AgNPs and AuNPs and showed the highest odema inhibition (84.61% and 79.28%, respectively). In the wound healing assay, CuONPs and TMNPs caused the highest percentages of inhibition (87.82% and 61.98%, respectively) for the wound compared to AgNPs and AuNPs. TMNPs and CuONPs were more efficient in restoring the tissue integrity of wounds than AgNPs and AuNPs. Accordingly, we recommend using TMNPs and CuONPs in the wound healing dressings.

Disproportional surface segregation in ligand-free gold-silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine.

Catalytic activity and toxicity of mixed-metal nanoparticles have been shown to correlate and are known to be dependent on surface composition. The surface chemistry of the fully inorganic, ligand-free silver-gold alloy nanoparticle molar fraction series, is highly interesting for applications in heterogeneous catalysis, which is determined by active surface sites which are also relevant for understanding their dissolution behavior in biomedically-relevant ion-release scenarios. However, such information has never been systematically obtained for colloidal nanoparticles without organic surface ligands and has to date, not been analyzed in a surface-normalized manner to exclude density effects. For this, we used detailed electrochemical measurements based on cyclic voltammetry to systematically analyze the redox chemistry of particle-surface-normalized gold-silver alloy nanoparticles with varying gold molar fractions. The study addressed a broad range of gold molar fractions (Ag90Au10, Ag80Au20, Ag70Au30, Ag50Au50, Ag40Au60, and Ag20Au80) as well as monometallic Ag and Au nanoparticle controls. Oxygen reduction reaction (ORR) measurements in O2 saturated 0.1 M KOH revealed a linear reduction of the overpotential with increasing gold content on the surface, probably attributed to the higher ORR activity of gold over silver, verified by monometallic Ag and Au controls. These findings were complemented by detailed XPS studies revealing an accumulation of the minor constituent of the alloy on the surface, e.g., silver surface enrichment in gold-rich particles. Furthermore, highly oxidized Ag surface site enrichment was detected after the ORR reaction, most pronounced in gold-rich alloys. Further, detailed CV studies at acidic pH, analyzing the position, onset potential, and peak integrals of silver oxidation and silver reduction peaks revealed particularly low reactivity and high chemical stability of the equimolar Au50Ag50 composition, a phenomenon attributed to the outstanding thermodynamic, entropically driven, stabilization arising at this composition.

Ligand-assisted morphology regulation of AuNi bimetallic nanocrystals for efficient hydrogen evolution.

We report the controllable synthesis of AuNi core-shell (c-AuNi) and Janus (j-AuNi) nanocrystals (NCs) with uniform shape, tunable size and compositions in the presence of trioctylphosphine (TOP) or triphenylphosphine (TPP). The morphology of the AuNi bimetallic NCs could be regulated by varying the structure and concentration of phosphine ligands. The ligand-directed structural evolution mechanism of AuNi bimetallic NCs was investigated and discussed in detail. When loaded on graphitic carbon nitride (GCN) for photocatalytic hydrogen generation, the obtained j-AuNi NCs showed much higher activity for hydrogen evolution than the monometallic (Au and Ni) counterparts, owing to the synergistic effect of plasmon enhanced light absorption from the Au portion and additional electron sink effect from the Ni portion. This work provides a promising route for preparing low-cost Au-based bimetallic catalysts with controllable morphologies and high activities for hydrogen production.

Photocatalytic oxidation of 5-hydroxymethylfurfural to furandicarboxylic acid over the Au-Ag/TiO2 catalysts under visible light irradiation

In this work, plasmonic monometallic Ag or Au nanoparticles (NPs) and bimetallic AuAg NPs supported on TiO2 with tunable bandgap structure were prepared by incipient impregnation method. Visible-light-driven photocatalytic oxidation of 5-hydroxymethylfurfural (5-HMF) to furandicarboxylic acid (FDCA) was used to evaluate their catalytic properties of the bimetallic catalysts. The incorporation of Au NPs into Ag NPs was capable of tuning their d-band centers to upshift toward the Fermi Level of the bimetallic catalysts, as evidenced by density function theory calculations and valence band XPS measurements. The bimetallic catalysts have narrower bandgap energies and better efficiencies in photogenerated charge separation and transfer, thus resulting in higher catalytic activities in the photocatalytic oxidation of HMF compared with the monometallic Au or Ag NPs catalyst. More interestingly, the monometallic Ag NPs catalyst only gave rise to an oxidized intermediate, i.e. 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), whereas the monometalic Au NPs and the bimetallic catalysts could afford FDCA because of their d-band center differences. The bimetallic catalysts also showed an excellent stability at least five successive runs in the photocatalytic oxidation of HMF to FDCA. This work offers a novel strategy for designing bimetallic catalysts used for the oxidation of 5-HMF to FDCA under visible light irradiation by mediating the d-band centers to upshift toward the Fermi Level.

Ethanol Electrooxidation at 1-2 nm AuPd Nanoparticles.

We report a systematic study of the electrocatalytic properties and stability of a series of 1-2 nm Au, Pd, and AuPd alloy nanoparticles (NPs) for the ethanol oxidation reaction (EOR). Following EOR electrocatalysis, NP sizes and compositions were characterized using aberration-corrected scanning transmission electron microscopy (ac-STEM) and energy dispersive spectroscopy (EDS). Two main findings emerge from this study. First, alloyed AuPd NPs exhibit enhanced electrocatalytic EOR activity compared to either monometallic Au or Pd NPs. Specifically, NPs having a 3:1 ratio of Au:Pd exhibit an ~8-fold increase in peak current density compared to Pd NPs, with an onset potential shifted ~200 mV more to the negative compared to Au NPs. Second, the size and composition of AuPd alloy NPs do not (within experimental error) change following 1.0 or 2.0 h chronoamperometry experiments, while monometallic Au NPs increase in size from 2 to 5 nm under the same conditions. Notably, this report demonstrates the importance of post-catalytic ac-STEM/EDS characterization for fully evaluating NP activity and stability, especially for 1-2 nm NPs that may change in size or structure during electrocatalysis.

Highly Efficient Catalysts of AuPd Alloy Nanoparticles Supported on 3D Ordered Macroporous Al2O3 for Soot Combustion

AbstractThe catalysts of Au−Pd bimetallic nanoparticles with different Au/Pd ratios supported on 3DOM Al2O3 were synthesized by micropores‐diffused reduction (MDR) method. Compared with supported monometallic Au or Pd catalysts, supported bimetallic Au−Pd nanoparticle catalysts, especially Au2‐Pd2/3DOM Al2O3, show higher catalytic activity for soot combustion due to good synergetic effects between gold and palladium. Au/Pd ratio has a significant influence on the chemical states and size of bimetallic nanoparticles. The co‐presence of Au is favorable for the formation of metallic Pd instead of PdO. And the size of Au−Pd bimetallic nanoparticles gradually decreases with increasing Au/Pd ratio. The effect of water in the reaction atmosphere and SO2‐presulfurization of the catalyst on the activity is also studied. It is unexpected that Au2‐Pd2/3DOM Al2O3 catalysts with SO2‐presulfurization has higher catalytic activity than the fresh catalysts. The increased activity is related to the formed surface aluminum sulfate and enhanced acidity.