AuPd Nanoparticles Research Articles

Synergistic Effects of Bimetallic AuPd and La2O3 in the Catalytic Reduction of NO with CO

Bimetallic AuPd nanoparticles supported on TiO2 are known to catalyze the reduction of NO with CO. Here, we investigated the effects of the addition of lanthanum oxide to a AuPd/TiO2 catalyst with a AuPd particle size of 2.1–2.2 nm. The addition of La2O3 enhanced the catalytic activity; for example, at 250 °C, there was 40.9% NO conversion and 49.3% N2-selectivity for AuPd/TiO2, and 100% NO conversion and 100% N2-selectivity for AuPd-La (1:1)/TiO2. The temperature requiring 100% NO conversion dropped from 400 °C to 200 °C by the simple post-impregnation of La2O3 onto AuPd/TiO2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with modulation excitation spectroscopy (MES) demonstrated that CO adsorption occurs first on Au atoms and then, within 80 s, moves onto Pd atoms. This transformation between two adsorption sites was facilitated by the addition of La2O3.

2-1-2 Highly selective synthesis of methanol from methane over CNTs supported Pd-Au nanoparticles catalyst at low temperature

2-1-2 Highly selective synthesis of methanol from methane over CNTs supported Pd-Au nanoparticles catalyst at low temperature

On the role of bismuth as modifier in AuPdBi catalysts: Effects on liquid-phase oxidation and hydrogenation reactions

There is much about the action of bismuth within heterogeneous catalysis that still require a deeper understanding. We observed that, when Bi was added to AuPd bimetallic nanoparticles (NPs) supported on activated carbon, Bi affected the activity and significantly alters the selectivity in two model liquid phase reactions, namely the oxidation of cinnamyl alcohol and the hydrogenation of cinnamaldehyde. A combination of transmission electron microscopy and X-ray absorption spectroscopy provided a detailed characterization of trimetallic AuPdBi systems. We propose that the introduction of bismuth on AuPd NPs results in a partial blockage of most active sites, limiting the occurrence of consecutive reactions.

Selective oxidation of methane to methanol using AuPd@ZIF-8

Selective methane conversion to alcohol derivatives remains an open challenge. Here, bimetallic catalyst, AuPd@ZIF-8, has been synthesized and demonstrated as an excellent catalyst in the presence of H2O2 and O2 under mild condition. Specifically, the yield for liquid oxygenated and methanol are 83.0 and 21.7 mmol gAuPd−1 h−1, with selectivity up to 89.5% and 21.9%, respectively. This high productivity may be due to the synergistic effect between AuPd nanoparticles and ZIF-8 framework. Oxygen-based isotopic tests reveal that oxygen serve as oxidants for this oxidation process. Methyl hydroperoxide is the primary product at early stage, which can be further oxidized.

Ternary Electrochemiluminescence Biosensor Based on DNA Walkers and AuPd Nanomaterials as a Coreaction Accelerator for the Detection of miRNA-141.

In this study, a ternary electrochemiluminescence (ECL) sensing platform coupled with a multiple signal amplification strategy was proposed for ultrasensitive detection of miRNA-141. The initial signal amplification was achieved via three-dimensional reduced graphene oxide (3D-rGO)@Au nanoparticles (NPs) to form an excellent conductive layer. Then, AuPd NPs as a coreaction accelerator was introduced into the N-(4-aminobutyl)-N-(ethylisoluminol) (ABEI)-H2O2 system to facilitate the transformation from H2O2 to excess superoxide anion radicals (O2•-), which further amplified the ECL emission of ABEI, leading to a significant increase of the ECL signal. Meanwhile, in the presence of miRNA-141 and T7 Exonuclease (T7 Exo), the self-assembled DNA swing arm can be driven to walk autonomously. The DNA walker reaction could result in the release of numerous labeled luminophores, which could react to achieve an extremely weak ECL signal. Surprisingly, the established ECL sensor platform for the detection of miRNA-141 demonstrated excellent sensitivity with a low detection limit of 31.9 aM in the concentration range from 100 aM to 1 nM. Consequently, the designed strategy greatly improves the luminous efficiency of the ternary ECL system and provides a special approach for the detection of nucleic acids and biomarkers in clinical and biochemical analysis.

Role of Femtosecond Pulsed Laser-Induced Atomic Redistribution in Bimetallic Au-Pd Nanorods on Optoelectronic and Catalytic Properties.

Utilizing solar energy for chemical transformations has attracted a growing interest in promoting the clean and modular chemical synthesis approach and addressing the limitations of conventional thermocatalytic systems. Under light irradiation, noble metal nanoparticles, particularly those characterized by localized surface plasmon resonance, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. Plasmonic nanoparticles enabling efficient absorption of light in the visible range have moderate catalytic activities. However, the catalytic performance of a plasmonic nanoparticle can be significantly enhanced by incorporating a highly catalytically active metal domain onto its surface. In this study, we demonstrate that femtosecond laser-induced atomic redistribution of metal domains in bimetallic Au-Pd nanorods (NRs) can enhance its photocurrent response by 2-fold compared to parent Au-Pd NRs. We induce structure changes on Au-Pd NRs by irradiating them with a femtosecond pulsed laser at 808 nm to precisely redistribute Pd atoms on AuNR surfaces, resulting in modified electronic and optical properties and, thereby, enhanced catalytic activity. We also investigate the trade-off between the effect of light absorption and catalytic activity by optimizing the structure and composition of bimetallic Au-Pd nanoparticles. This work provides insight into the design of hybrid plasmonic-catalytic nanostructures with well-tailored geometry, composition, and structure for solar-fuel-based applications.

Methane Oxidation to Methanol in Water.

Methane represents one of the most abundant carbon sources for fuel or chemical production. However, remote geographical locations and high transportation costs result in a substantial proportion being flared at the source. The selective oxidation of methane to methanol remains a grand challenge for catalytic chemistry due to the large energy barrier for the initial C-H activation and prevention of overoxidation to CO2. Indirect methods such as steam reforming produce CO and H2 chemical building blocks, but they consume large amounts of energy over multistage processes. This makes the development of the low-temperature selective oxidation of methane to methanol highly desirable and explains why it has remained an active area of research over the last 50 years.The thermodynamically favorable oxidation of methane to methanol would ideally use only molecular oxygen. Nature effects this transformation with the enzyme methane monooxygenase (MMO) in aqueous solution at ambient temperature with the addition of 2 equiv of a reducing cofactor. MMO active sites are Fe and Cu oxoclusters, and the incorporation of these metals into zeolitic frameworks can result in biomimetic activity. Most approaches to methane oxidation using metal-doped zeolites use high temperature with oxygen or N2O; however, demonstrations of catalytic cycles without catalyst regeneration cycles are limited. Over the last 10 years, we have developed Fe-Cu-ZSM-5 materials for the selective oxidation of methane to methanol under aqueous conditions at 50 °C using H2O2 as an oxidant (effectively O2 + 2 reducing equiv), which compete with MMO in terms of activity. To date, these materials are among the most active and selective catalysts for methane oxidation under this mild condition, but industrially, H2O2 is an expensive oxidant to use in the production of methanol.This observation of activity under mild conditions led to new approaches to utilize O2 as the oxidant. Supported precious metal nanoparticles have been shown to be active for a range of C-H activation reactions using O2 and H2O2, but the rapid decomposition of H2O2 over metal surfaces limits efficiency. We identified that this decomposition could be minimized by removing the support material and carrying out the reaction with colloidal AuPd nanoparticles. The efficiency of methanol production with H2O2 consumption was increased by 4 orders of magnitude, and crucially it was demonstrated for the first time that molecular O2 could be incorporated into the methanol produced with 91% selectivity. The understanding gained from these two approaches provides valuable insight into possible new routes to selective methane oxidation which will be presented here in the context of our own research in this area.

Shape Changes in AuPd Alloy Nanoparticles Controlled by Anisotropic Surface Stress Relaxation.

The shape of AuPd nanoparticles is engineered by surface stress relaxation, achieved by varying the Au content in nanoparticles of Pd-rich compositions. AuPd nanoparticles are grown in the gas phase for several compositions and growth conditions. Their structure is atomically resolved by HRTEM/STEM and EDX. In pure Pd distributions the dominant structures are FCC truncated octahedra (TO), while increasing the Au content there is a transition to icosahedral (Ih) structures in which Au atoms are preferentially placed at the nanoparticle surface. The transition is sharper for growth conditions closer to equilibrium. The physical origin of the transition is determined with the aid of computer simulations. Global optimization searches and free energy calculations confirm that Ih become the equilibrium structure for increasing the Au content. Atomic stress calculations demonstrate that the TO → Ih shape change is caused by a better relaxation of anisotropic surface stress in icosahedra.

Bimetal Au-Pd decorated hierarchical WO3 nanowire bundles for gas sensing application

This study has developed a simple but effective synthesis method to deposit bimetal Au-Pd nanoparticles onto WO3 hierarchical bundle nanowires through an in-situ redox reaction in a reducing aqueous medium. Hydrothermal method was used for the synthesis of WO3 hierarchical bundles ultrathin nanowire subunits, and the mechanisms controlling the segregation behavior and growth based on Na2SO4, citric acid, and ethylene glycol are discussed. It was found that the Pd-WO3 and/or Au-Pd-WO3 nanocomposites decorated with Au 2.4 wt% and Pd 0.48 wt% showed exemplary sensitivity (S) for 50 ppm n-butanol as S = 91 at 200 °C, approximately 14 and 1.4 times better than pristine WO3 (S = 5.7) and Pd-WO3 (S = 59), respectively. Moreover, the Pd-WO3 sensing results demonstrated that the Pd decoration could significantly reduce the operating temperature, similarly to the Au-Pd-WO3 sensor, which is particularly effective for n-butanol gas among common volatile organic compounds (VOCs). The analysis demonstrates that the bimetal Au-Pd decoration have resulted a synergistic effect in boosting the sensitivity of the WO3-based sensor toward n-butanol gas. The underlying sensing mechanism of such an Au-Pd-WO3 hybrid nanostructure is further discussed, based on chemical and electronic sensitizations in promoting the spillover of oxygen species and rectifying Schottky barriers at the interface of noble metal(s) and semiconductor oxide (e.g., WO3). This work may be beneficial for designing a unique Au-Pd-WO3 sensor with great potential to develop oxide-based sensors for detecting other hazardous gases at low temperature.

The Direct Synthesis of Hydrogen Peroxide over AuPd Nanoparticles: An Investigation into Metal Loading

The direct synthesis of H2O2 from molecular H2 and O2 over AuPd catalysts, supported on TiO2 and prepared via an excess chloride co-impregnation procedure is investigated. The role of Au:Pd ratio on the catalytic activity towards H2O2 formation and its subsequent degradation is evaluated under conditions that have previously been found to be optimal for the formation of H2O2. The combination of relatively small nanoparticles, of mixed Pd-oxidation state is shown to correlate with enhanced catalytic performance. Subsequently, a detailed study of catalytic activity towards H2O2 synthesis as a function of AuPd loading was conducted, with a direct correlation between catalytic activity and metal loading observed.Graphic

Bimetallic PdAu Nanoparticles in Amine-Containing Metal–Organic Framework UiO-66 for Catalytic Dehydrogenation of Formic Acid

Ultrafine and well-dispersed PdAu bimetallic nanoparticles (ca. 1.4 nm) are successfully immobilized on amine-containing UiO-66 frameworks (NH2-UiO-66) via a double-solvent impregnation method. By ...

Heterostructures based on Pd–Au nanoparticles and cobalt phthalocyanine for hydrogen chemiresistive sensors

In this work, the effect of Pd, Au and PdAu nanoparticles on sensor response of cobalt phthalocyanine films to hydrogen was studied. For this purpose, novel heterostructures based on cobalt phthalocyanine and PdAu nanoalloys were obtained by a combination of vacuum thermal evaporation and pulsed metalorganic chemical vapor deposition (MOCVD) and investigated as active layers for hydrogen detection. The structural features and phase composition of the prepared heterostructures were studied by the techniques of X-ray diffraction, transmission electron microscopy and electron diffraction. The concentration of metal nanoparticles in the samples was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The chemiresistive sensor response of CoPc/M (M = Pd, Au, Pd0.2Au0.8 and Pd0.8Au0.2) to hydrogen (100–400 ppm, room temperature) was compared with that of bare CoPc films. It was shown that the sensor response of the investigated heterostructures to hydrogen (300 ppm) increased in the order CoPc (0.2%) < CoPc/Pd0.2Au0.8 (1.9%) ~ CoPc/Au (2.2%) < CoPc/Pd (2.7%) < CoPc/Pd0.8Au0.2 (5.6%).

Organotrialkoxysilane-Functionalized Noble Metal Monometallic, Bimetallic, and Trimetallic Nanoparticle Mediated Non-Enzymatic Sensing of Glucose by Resonance Rayleigh Scattering.

Organotrialkoxysilanes like 3-aminopropyltrimethoxysilane (3-APTMS)-treated noble metal cations were rapidly converted into their respective nanoparticles in the presence of 3-glycidoxypropylytrimethoxysilane (3-GPTMS). The micellar activity of 3-APTMS also allowed us to replace 3-GPTMS with other suitable organic reagents (e.g., formaldehyde); this approach has significant advantages for preparing bimetallic and trimetallic analogs of noble metal nanoparticles that display efficient activity in many practical applications. The formation of monometallic gold, silver, and palladium nanoparticles, bimetallic Ag-Pd, and Au-Pd nanoparticles at various ratios of noble metal cations, and trimetallic Ag-Au-Pd nanoparticles were studied; their biocatalytic activity in non-enzymatic sensing of glucose based on monitoring synchronous fluorescence spectroscopy (SFS) was assessed. Of these nanoparticles, Au-Pd made with an 80:20 Au:Pd ratio displayed excellent catalytic activity for glucose sensing. These nanoparticles could also be homogenized with Nafion to enhance the resonance Rayleigh scattering (RRS) signal. In this study, the structural characterization of noble metal nanoparticles as well as bi- and tri-metallic nanoparticles in addition to their use in non-enzymatic sensing of glucose are reported.

Hydrogen Evolution on Reduced Graphene Oxide-Supported PdAu Nanoparticles

Hydrogen evolution reaction (HER) was investigated on reduced graphene oxide (rGO)-supported Au and PdAu nanoparticles in acid solution. The graphene spread over glassy carbon (rGO/GC) was used as a support for the spontaneous deposition of Au and Pd. The resulting Au/rGO and PdAu/rGO electrodes were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Phase AFM images have shown that the edges of the rGO sheets were active sites for the deposition of both Au and Pd. XPS analysis revealed that the atomic percentages of both Au and PdAu nanoparticles were slightly higher than 1%. The activity of the PdAu/rGO electrode for the HER was remarkably high, with the overpotential close to zero. HER activity was stable over a 3 h testing time, with a low Tafel slope of approx. −46 mV/dec achieved after prolonged hydrogen evolution at a constant potential.

Effective Intratumoral Retention of [103 Pd]AuPd Alloy Nanoparticles Embedded in Gel-Forming Liquids Paves the Way for New Nanobrachytherapy.

Local application of radioactive sources as brachytherapy is well established in oncology. This treatment is highly invasive however, due to the insertion of millimeter sized metal seeds. The authors report the development of a new concept for brachytherapy, based on gold-palladium (AuPd) alloy nanoparticles, intrinsically radiolabeled with 103 Pd. These are formulated in a carbohydrate-ester based liquid, capable of forming biodegradable gel-like implants upon injection. This allows for less invasive administration through small-gauge needles. [103 Pd]AuPd nanoparticles with sizes around 20nm are prepared with radiolabeling efficiencies ranging from 79% to >99%. Coating with the hydrophobic polymer poly(N-isopropylacrylamide) leads to nanoparticle diameters below 40nm. Dispersing the nanoparticles in ethanol with water insoluble carbohydrate esters gives "nanogels", a low viscosity liquid capable of solidifying upon injection into aqueous environments. Both nanoparticles and radioactivity are stably retained in the nanogel over 25 days (>99%) after formation in aqueous buffers. Animals bearing CT26 murine tumors are injected intratumorally with 25 MBq of the 103 Pd-nanogel, and display tumor growth delay and significantly increase median survival times compared with control groups. Excellent retention in the tumor of both the 103 Pd and the nanoparticle matrix itself is observed, demonstrating a potential for replacing currently used brachytherapy seeds.

Plasmonic Au–Pd Bimetallic Nanocatalysts for Hot-Carrier-Enhanced Photocatalytic and Electrochemical Ethanol Oxidation

Gold–palladium (Au–Pd) bimetallic nanostructures with engineered plasmon-enhanced activity sustainably drive energy-intensive chemical reactions at low temperatures with solar simulated light. A series of alloy and core–shell Au–Pd nanoparticles (NPs) were prepared to synergistically couple plasmonic (Au) and catalytic (Pd) metals to tailor their optical and catalytic properties. Metal-based catalysts supporting a localized surface plasmon resonance (SPR) can enhance energy-intensive chemical reactions via augmented carrier generation/separation and photothermal conversion. Titania-supported Au–Pd bimetallic (i) alloys and (ii) core–shell NPs initiated the ethanol (EtOH) oxidation reaction under solar-simulated irradiation, with emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. Plasmon-assisted complete oxidation of EtOH to CO2, as well as intermediary acetaldehyde, was examined by monitoring the yield of gaseous products from suspended particle photocatalysis. Photocatalytic, electrochemical, and photoelectrochemical (PEC) results are correlated with Au–Pd composition and homogeneity to maintain SPR-induced charge separation and mitigate the carbon monoxide poisoning effects on Pd. Photogenerated holes drive the photo-oxidation of EtOH primarily on the Au-Pd bimetallic nanocatalysts and photothermal effects improve intermediate desorption from the catalyst surface, providing a method to selectively cleave C–C bonds.

Bimetallic AuPd Alloy Nanoparticles Decorated on Macroporous WO3 Supports for Selective Detection of Acetone

Three-dimensional ordered macroporous (3DOM) metal-oxide-based materials have received much attention in the field of gas sensing for their potential in breath acetone analysis. The major challenge of metal-oxide-based sensors for analyzing acetone from exhalation is their poor selectivity in the complex mixture of breath. Functionalizing of sensitive materials by noble metal nanoparticles (NPs) is one of the efficient methods to improve gas sensing selectivity, but noble metal NPs are prone to aggregation at the working temperature. To address these issues, we herein have constructed a series of AuPd/WO3 materials by depositing bimetallic AuPd alloy NPs on the surface of 3DOM WO3 supports. The amount of AuPd NP content and Au/Pd molar ratio are optimized on the basis of acetone responses. The sensor based on the optimal AuPd alloy NP-decorated 3DOM WO3 (AuPdW) exhibits high responses to trace acetone with rapid response/recovery speeds. Besides, the AuPdW sensor presents excellent acetone selectivity and good reproducibility. More attractively, the responses of the sensor to acetone exhibit no noticeable decline over 8 weeks, indicating good long-term stability of the synthesized material. We suggest that the improved responses and excellent selectivity to acetone are ascribed to the synergistic effect of electronic sensitization and chemical sensitization of AuPd alloy NPs. The good long-term stability of AuPdW is attributed to the steric hindrance effect of 3DOM structure to AuPd NPs.

Hierarchical porous bowl-like nitrogen-doped carbon supported bimetallic AuPd nanoparticles as nanoreactors for high efficient catalytic oxidation of HMF to FDCA

Efficient nanoreactors for the catalytic oxidation of the key platform compound HMF to the high value-added chemical FDCA are highly desirable in the field of biomass transformation. Herein, hierarchical porous bowl-like nitrogen-doped carbon supported AuPd bimetallic (AuPd/pBNxC) nanoreactors were synthesized by the following steps: precipitation polymerization, carbonization, SiO2 sphere removal, and sol curing. By changing the amount of nitrogen doping and removing the template, AuPd/pBNxC nanoreactors with a hierarchical porous structure and adjustable basicity were prepared. The alkaline sites of NxC carriers provided anchoring sites for metals and had a certain adsorption affinity for HMF and its intermediates. Theoretical calculations and adsorption experiments indicated that the doped nitrogen significantly enhanced the combining capacity between the HMF molecule and nanoreactors. The nanoreactor was used for the tandem oxidation of HMF to FDCA in water, and the highest FDCA yield of 97.6% could be obtained under optimum reaction conditions. The reaction process was evaluated by kinetics calculations, and the oxidation of FFCA to FDCA was confirmed as the rate-determining step. The regeneration experiments showed that the AuPd/pBNxC nanoreactors could be recycled and reused at least five times without an obvious loss in catalytic activity.

Effect of Pd Ions on the Generation of Ag and Au Heterogeneous Nanoparticles Using Laser Ablation in Liquid

Heterogeneous Ag/Au nanoparticles combined with Pd ions were generated by irradiating Ag/Au metal targets in a Pd solution with nanosecond and femtosecond lasers. AgPd and AuPd nanoparticles were generated by laser fragmentation and bonded. We numerically analyzed the hot spots with electromagnetic field enhancement of nanoparticles of different sizes separated by various distances. AgPd and AuPd nanoparticles differing in diameter were generated and showed different characteristics compared to typical core-shell heterogeneous nanoparticles. Pd ions played an important role in the generation of nanoparticles in liquid via laser ablation. The femtosecond laser produced both pure and heterogeneous nanoparticles of uniform size. The nanosecond laser produced pure nanoparticles with a relatively non-uniform size, which developed into spherical heterogeneous nanoparticles with a uniform (small) size in the presence of Pd ions. These nanoparticles could optimize applications such as photothermal therapy and catalysis.

Bimetallic AuPd Nanoparticles Loaded on Amine-Functionalized Porous Boron Nitride Nanofibers for Catalytic Dehydrogenation of Formic Acid

Formic acid (FA) has been considered as a promising hydrogen energy carrier due to its nontoxicity, high energy density, easy storage/transport, etc. However, the development of decent FA dehydroge...