Au Pd Bimetallic Nanoparticles Research Articles

Modification of Surface Bond Au Nanospheres by Chemically and Plasmonically Induced Pd Deposition.

In this work we investigated methods of modifying gold nanospheres bound to a silicon surface by depositing palladium onto the surfaces of single nanoparticles. Bimetallic Au-Pd nanoparticles can thus be gained for use in catalysis or sensor technology. For Pd deposition, two methods were chosen. The first method was the reduction of palladium acetate by ascorbic acid, in which the amounts of palladium acetate and ascorbic acid were varied. In the second method we utilized light-induced metal deposition by making use of the plasmonic effect. Through this method, the surface bond nanoparticles were irradiated with light of wavelengths capable of inducing plasmon resonance. The generation of hot electrons on the particle surface then reduced the palladium acetate in the vicinity of the gold nanoparticle, resulting in palladium-covered gold nanospheres. In our studies we demonstrated the effect of both enhancement methods by monitoring the particle heights over enhancement time by atomic force microscopy (AFM), and investigated the influence of ascorbic acid/Pd acetate concentration as well as the impact of the irradiated wavelengths on the enhancement effect. It could thus be proven that both methods were valid for obtaining a deposition of Pd on the surface of the gold nanoparticles. Deposition of Pd on the gold particles using the light-assisted method could be observed, indicating the impact of the plasmonic effect and hot electron for Pd acetate reduction on the gold particle surface. In the case of the reduction method with ascorbic acid, in addition to Pd deposition on the gold nanoparticle surface, larger pure Pd particles and extended clusters were also generated. The reduction with ascorbic acid however led to a considerably thicker Pd layer of up to 54 nm in comparison to up to 11 nm for the light-induced metal deposition with light resonant to the particle absorption wavelength. Likewise, it could be demonstrated that light of non-resonant wavelengths was not capable of initiating Pd deposition, since a growth of only 1.6 nm (maximum) was observed for the Pd layer.

Bimetallic AuPd@CeO2 Nanoparticles Supported on Potassium Titanate Nanobelts: A Highly Efficient Catalyst for the Reduction of NO with CO

A nanocomposite consisting of bimetallic AuPd nanoparticles, which were modified with CeO2 (AuPd@CeO2), and deposited on potassium titanate nanobelts (KTN) as support, is shown to exhibit outstanding catalytic performance in the selective catalytic reduction of NO with CO. Transmission electron microscopy and energy dispersive X-Ray elemental mapping indicated that the AuPd nanoparticles surrounded by CeO2 were well-mixed forming an alloy. The potassium titanate support consisted of 1–3 µm long and 8–14 nm wide nanobelts. The AuPd@CeO2/KTN catalyst showed full NO conversion at 100 % selectivity to N2 at a gas-hourly space velocity (GHSV) of 15,000 h−1 and 200 °C. The outstanding performance of the AuPd@CeO2/KNT catalyst is attributed to favorable synergies between its components. Corresponding monometallic Au catalysts supported on KTN (Au@CeO2/KNT), as well as bimetallic AuPd supported on TiO2 (AuPd@CeO2/TiO2), showed inferior catalytic performance, indicating the absence of a beneficial synergy between the different components. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with modulation excitation spectroscopy (MES) proved that alloying of Au with Pd enhances the ability to adsorb CO and NO on the surface in an on-top configuration and that the deposition of the bimetallic AuPd nanoparticles on KTN facilitates the crucial formation of isocyanate (-NCO) species, resulting in high conversion and selectivity.

Pd Single-Atom Sites on the Surface of PdAu Nanoparticles: A DFT-Based Topological Search for Suitable Compositions.

Structure of model bimetallic PdAu nanoparticles is analyzed aiming to find Pd:Au ratios optimal for existence of Pd1 single-atom surface sites inside outer Au atomic shell. The analysis is performed using density-functional theory (DFT) calculations and topological approach based on DFT-parameterized topological energy expression. The number of the surface Pd1 sites in the absence of adsorbates is calculated as a function of Pd concentration inside the particles. At low Pd contents none of the Pd atoms emerge on the surface in the lowest-energy chemical orderings. However, surface Pd1 sites become stable, when Pd content inside a Pd-Au particle reaches ca. 60%. Further Pd content increase up to almost pure Pd core is accompanied by increased concentration of surface Pd atoms, mostly as Pd1 sites, although larger Pd ensembles as dimers and linear trimers are formed as well. Analysis of the chemical orderings inside PdAu nanoparticles at different Pd contents revealed that enrichment of the subsurface shell by Pd with predominant occupation of its edge positions precedes emergence of Pd surface species.

Fabrication of Pd–Au Clusters by In Situ Spontaneous Reduction of Reductive Layered Double Hydroxides

In this work, layered double hydroxides (LDHs) including the variable valence Co2+ ions (CoAl-LDHs) is discovered to be capable of serving as the support and the reducing agent for the fabrication of well-distributed PdAu nanoparticles because of the low potential for reduction. Specifically, the active metal precursors undergo the redox process, in which Co2+ is oxidized to Co3+, while active metal ions are successfully reduced to bimetallic PdAu nanoparticles with the dispersion of 73%. Furthermore, the obtained catalysts are evaluated in the selective oxidation of benzyl alcohol as the probing reaction to explore the catalytic behavior. As for intrinsic activity, PdAu/CoAl-LDHs derived by the above in situ spontaneous reduction exhibits activation energy of 62.4 kJ mol−1, much lower than that of PdAu/CoAl-LDHs prepared by sol-immobilization. When the reaction time reaches to 4 h, the benzaldehyde selectivity over the former catalyst is up to 94%, originating from the surface electron starvation of active metals that promots the hydroxyl groups reacting with O2 to produce benzaldehyde.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au–Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore–Pdshell (Au@Pd–SiO2) and Pdcore–Aushell (Pd@Au–SiO2) nanoparticles were synthesized. The structures and compositions of the core–shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core–shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au–Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore–Aushell structure displayed superior activity over the Aucore–Pdshell structure which could be attributed to the higher stability and uniform Au–Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

AuPd bimetallic nanoparticles supported on reduced graphene oxide nanosheets as catalysts for hydrogen generation from formic acid under ambient temperature

Monometallic Au and Pd, and bimetallic AuxPdy (x/y mole ratio Au/Pd: 3 : 1, 1 : 1 and 1 : 3) catalysts supported on reduced graphene oxide (rGO) have been synthesised by the sol-immobilization method.

Synthesis of ultrafine AuPd bimetallic nanoparticles using a magnetite-cored poly(propyleneimine) dendrimer template and its sustainable catalysis of the Suzuki coupling reaction

A rational synthesis of magnetically recyclable PPI dendrimer encapsulated AuPd bimetallic nanoparticle and its catalytic examination in the Suzuki coupling reaction.

Metal phenanthroline-based porous polymeric hybrid catalysts for direct conversion of methane

The direct conversion of tremendous greenhouse gas methane into various value-added chemical products or energy fuels is not only a concern associated with an economic interest but also related to environmental protection. However, neither industry nor academia has an effective or low-cost way to directly achieve this result. Herein, a high specific area (962 m2 g−1) porous organic polymer was designed and used as a substance to support catalytic active sites, including PdBr2, Pd(OAc)2, and well-dispersed AuPd bimetallic nanoparticles which were reduced via hydrogen flow. The as-synthesized catalysts (HNU-2 and HNU-3) can not only maintain the porous and stable structure of their pristine matrix but also show extremely high catalytic performance in methane direct transformation systems for preparing methanol derivative methyl trifluoroformate. Our simple strategy provides a complementary alternative to application of methane via an efficient one-step conversion procedure in order to reduce its impact on climate change and obtain value-added chemicals.

Au-Pd nanoparticles immobilized on TiO2 nanosheet as an active and durable catalyst for solvent-free selective oxidation of benzyl alcohol

TiO2nanocrystals with controlled facets have been extensively investigated due to their excellent photocatalytic performance in sustainable and green energy field. However, the applications in thermal catalysis without applying UV irradiation are comparably less and the identification of their intrinsic roles, especially the different catalytic behaviors of each crystal facet, remains not fully recognized. In this study, bimetallic AuPd nanoparticles supported on anatase TiO2 nanosheets exposing {001} facets or TiO2 nanospindles exposing {101} as a catalyst were prepared by sol-immobilization method and used for solvent-free benzyl alcohol oxidation. The experimental results indicated that the exposed facet of the support has a significant effect on the catalytic performance. AuPd/TiO2-001 catalyst exhibited a higher benzyl alcohol conversion than that of the AuPd/TiO2-101. Meanwhile, all the prepared AuPd/TiO2 catalysts were characterized by XRD, ICP-AES, XPS, BET, TEM, and HRTEM. The results revealed that the higher number of oxygen vacancies in TiO2-sheets with the exposed {001} facets of higher surface energy could be responsible for the observed enhancement in the catalytic performance of benzyl alcohol oxidation. The present study displays that it is plausible to enhance the catalytic performance for the benzyl alcohol oxidation by tailoring the exposed facet of the TiO2 as a catalyst support.

Gold-Palladium Bimetallic Nanoparticles for Inducing Surface Plasmon Resonance to Catalyze Ethanol Oxidation

Gold-palladium (Au-Pd) bimetallic nanoparticles were prepared as a series of alloy and core-shell nanostructures to synergistically couple plasmonic (Au) and catalytic (Pd) metals to tailor the optical and catalytic properties. Catalysts utilizing plasmonic metals that exhibit a localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement via augmented carrier generation/separation and photothermal conversion. Titania-supported Au-Pd bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) oxidation reaction, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Plasmonically-assisted photocatalytic oxidation of EtOH to CO2 under solar simulated-light irradiation was studied by monitoring the yield of gaseous products via suspended particle photocatalysis and electrochemical methods. Results are correlated with Au-Pd composition and homogeneity to maintain SPR-induced charge separation and mitigate the carbon monoxide poisoning effects on Pd. Under solar simulated conditions, carrier generation/separation and photothermal conversion was achieved, resulting in the photogenerated “hot” holes driving the photo-oxidation of EtOH primarily on the AuPd, providing a method to selectively cleave C-C bonds. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

Biocompatible functionalized AuPd bimetallic nanoparticles decorated on reduced graphene oxide sheets for photothermal therapy of targeted cancer cells

Graphene, which is a unique 2D nanomaterials has received widespread attention for photothermal therapy (PTT) application. Here, we have designed the nanocomposite using polydopamine (PDA) functionalized reduced graphene oxide (rGO) nanosheets and bimetallic AuPd nanoparticles (NPs). The bimetallic AuPd nanoparticles decorated PDA functionalized rGO (AuPd-rGO/PDA) nanocomposite is synthesized by simple chemical reduction technique resulting in an average size of AuPd bimetallic nanostructure of 4.18 nm. The photothermal activity of the AuPd-rGO/PDA nanocomposite is explored under the irradiation of near infrared (NIR) laser sources of wavelength 915 nm. The temperature rises nearly 51 ± 3 °C within 3 min of irradiation NIR laser light resulting in the ablation of MDAMB-231 cancer cells up to concentration of 25 μg mL−1 of AuPd-rGO/PDA nanocomposite. This high performance of the ablation of cancer cells by photothermal therapy technique was facilitated using a low concentration of the nanocomposite by the synergistic effects of the bimetallic AuPd as well as rGO and PDA functionalization. The AuPd-rGO/PDA nanocomposite demonstrated the high biocompatibility towards normal healthy cell lines (L929) and exhibits survival efficiency of more than 85%. We also demonstrated the biocompatibility of the AuPd-rGO/PDA nanocomposite materials on the zebrafish embryos (Danio rerio). This work thus illustrates that the AuPd-rGO/PDA nanocomposite could behave as favourable nanoplatform for tumor therapeutics.

Continuous Flow Synthesis of Bimetallic AuPd Catalysts for the Selective Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

AbstractThe production of 2,5‐furandicarboxylic acid (FDCA) from the selective oxidation of 5‐hydroxymethylfurfural (HMF) is a critical step in the production of biopolymers from biomass‐derived materials. In this study, we report the catalytic performance of monometallic Au and Pd, and bimetallic AuPd nanoparticles with different Au : Pd molar ratios synthesised under continuous flow conditions using a millifluidic set‐up and subsequently deposited onto titanium dioxide as the chosen support. This synthetic technique provided a better control over mean particle size and metal alloy composition, that resulted in higher FDCA yield when the catalysts were compared to similar batch‐synthesised materials. A 99% FDCA yield was obtained with the millifluidic‐prepared AuPd/TiO2 catalyst (Au : Pd molar composition of 75 : 25) after being calcined and reduced at 200 °C. The heat treatment caused a partial removal of the protective ligand (polyvinyl alcohol) encapsulating the nanoparticles and so induced stronger metal‐support interactions. The catalyst reusability was also tested, and showed limited particle sintering after five reaction cycles.

5-Hydroxymethylfurfural and Furfural Base-Free Oxidation over AuPd Embedded Bimetallic Nanoparticles

The heterogeneous catalytic partial oxidation of alcohols and aldehydes in the liquid phase usually needs the addition of a homogeneous base, which in turn makes the products’ recovery cumbersome, and can further induce undesired side reactions. In the present work, we propose the use of novel catalysts based on metallic Au, Pd and bimetallic AuPd nanoparticles embedded in a titanosilicate matrix. The as-prepared catalysts showed good efficiency in the base-free partial oxidation of furfural and 5-hydroxymethylfurfural. Au4Pd1@SiTi catalyst showed high selectivity (78%) to monoacids (namely, 5-formyl-2-furancarboxylic acid and 5-hydroxymethyl-2-furancarboxylic acid) at 50% 5-hydroxymethylfurfural (HMF) conversion. The selectivity even reached 83% in the case of furfural oxidation to furoic acid (at 50% furfural conversion). The performances of the catalysts strongly depended on the Au–Pd ratio, with an optimal value of 4:1. The pH of the solution was always below 3.5 and no leaching of metals was observed, confirming the stabilization of the metal nanoparticles within the titanosilicate host matrix.

Electrocatalytic activity of Pd–Au nanoalloys during methanol oxidation reaction

Methanol fuel cells are very promising power source due to its high efficiency and low emissions of pollutants but their commercialization is hindered by development of the effective catalysts. Bimetallic nanostructured catalysts have been used to increase the effectiveness of methanol electrooxidation. Their high electrocatalytic activity can be accounted largely by the difference in electronegativity of two metals (e.g. Pd and Au), that resulting in gradual Auδ+→Auδ– transition with the increase in Pd content. Therefore, gold-enriched bimetallic Pd-Aunano were recommended as catalysts for oxidation processes since they are characterized by the presence of Auδ+ on their surface. Deposition of Pd, Au and Pd–Au nanoparticles (~50–350 nm) were carried out in dimethyl sulfoxide by pulsed mode of electrolysis directly on electrode surface. Cyclic voltammetry was the main method to study catalytic properties of the modified electrode in the anode oxidation process of methanol. It was found that oxidation rate on the electrode surface modified by bimetallic Pd–Au nanoparticles is ~1.5 times higher as compared to that in the case of electrodes modified by Pd or Au monometallic nanoparticles individually. In order to find highly active, selective, and stable catalysts for methanol electrocatalytic oxidation reaction additional studies are needed to understand the role of electrode surface charge and local OH− ions concentration from alkali solution.

Investigations of supported Au-Pd nanoparticles on synthesized CeO2 with different morphologies and application in solvent-free benzyl alcohol oxidation

Au-Pd bimetallic nanoparticles immobilized on series of CeO2 supports with different morphologies, e.g., rod, cube, and polyhedrons were prepared through the deposition-precipitation method with a consequent investigation on their catalytic performances for benzyl alcohol oxidation in the absence of solvent. The experimental results exhibited that the morphology of CeO2 has a markedly impact on the catalytic performance of Au-Pd/CeO2. In which Au-Pd supported on CeO2 rod could achieve higher benzyl alcohol conversion than that supported on CeO2 polyhedrons and CeO2 cube, however, CeO2 cube supported Au-Pd showed the highest selectivity towards the production of benzaldehyde. ICP-AES, XRD, Raman, N2-BET, TEM, HAADF-STEM, and XPS were conducted to characterize the catalysts. The results revealed that the excellent behavior of Au-Pd/CeO2-rod in benzyl alcohol oxidation was closely related with the smaller size of CeO2 particle, the higher concentration of oxygen defects in support and the higher number of Ce3+ and Pd2+ species on the catalyst surface. The present study on the morphologies of CeO2 support in solvent-free benzyl alcohol oxidation would offer a notable approach for the future catalyst design.

One-pot synthesis of Pd20-xAux nanoparticles embedded in nitrogen doped graphene as high-performance electrocatalyst toward methanol oxidation

Mixed Pd–Au bimetallic nanoparticles embedded nitrogen doped graphene composites (PdAu/NG180) are explored for efficient electrocatalytic oxidation of methanol. A simple hydrothermal one-pot polyol method, involving simultaneous reduction of both Pd and Au, is utilized for the synthesis of Pd20-xAux/NG180 (x wt % = 0, 5, 10 and 15). This method is of multiple advantages such as inexpensiveness, reagent-free and environment-friendly being surfactant free. The morphology, crystal structure and chemical composition of NG180, Pd/NG180 and Pd20-xAux/NG180 catalysts are analyzed by XRD, FESEM-EDX, TEM, XPS and Raman spectroscopy methods. Electrocatalytic activities of PdAu/NG180 nanocomposites toward methanol oxidation reaction (MOR) in alkaline media are investigated by cyclic voltammetry, chronoamperometry and CO stripping measurements. Pd20-xAux/NG180 exhibited an increase in the electroactive surface area of Pd to twice by the coexistence of Au. In cyclic voltammetry studies, Pd10Au10/NG180 catalyst exhibits highest peak current density for MOR and is 1.5 times highly efficient compared to Pd20/NG180 with an enhanced shift in the onset potential by 140 mV to lower overpotentials. Besides, Pd10Au10/NG180 catalyst exhibited enhanced electroactive surface area and long-time durability in comparison to Pd20/NG180 catalyst. The steady state current density for MOR observed with Pd10Au10/NG180 at the end of 4000 s (98 mA mg−1Pd) is higher than those observed with all the other catalysts at the end of mere 1000 s alone (97, 61, and 32 mA mg−1Pd). The promising high electrocatalytic activity of Pd10Au10/NG180 is well corroborated from CO stripping experiments that the specific adsorption of CO onto Pd10Au10/NG180 (0.71 C m−2) is merely half to that observed onto Pd20/NG180 (1.49 C m−2).

Self-reduction bimetallic nanoparticles on ultrathin MXene nanosheets as functional platform for pesticide sensing

Two-dimensional (2D) transition metal carbides and nitrides, named MXene, appear promising application prospects in sensor filed. Metal nanoparticles, especially bimetallic nanoparticles, are the superior nanocatalyst, which process excellent features due to the high specific surface area and synergistic catalytic capacity. Using ultrathin MXene nanosheets as the natural reducing agent and support, we prepare the shape-controlled Au-Pd bimetallic nanoparticles via a self-reduction process at room temperature in a short time, which can well enhance the catalytic performance and are benefit for the acetylcholinesterase immobilization. Based on their desired properties, we propose a disposable electrochemical biosensor for the detection of organophosphorus pesticide using the multi-dimensional nanocomposites (MXene/Au-Pd) as the functional platform. Under the optimized conditions, our fabricated biosensor exhibits a favorable linear relationship with the concentration of paraoxon from 0.1 to 1000 μg L−1, with a low detection limit of 1.75 ng L−1. Furthermore, the biosensor can be applied for paraoxon detection in pear and cucumber samples, providing an effective and useful avenue for the applicability of novel 2D nanomaterials in biosensing field.

(Amazon Catalyst at ECS Grant Winner) Enhancing the Rate of Electrocatalytic Conversion of N2 to NH3 Using Bimetallic Au-Pd Nanoparticles

Ammonia is one of the widely produced chemicals in the world, with broad applications in producing nitrogen-based fertilizer, energy, and in the pharmaceutical industry. The current industrial method for ammonia production is energy intensive and heavily relies on fossil fuels, which are responsible for environmental pollution. To meet ammonia demands, it is necessary to develop sustainable and environmentally friendly production methods that consume significantly less energy than the current methods. Here, the use of hollow gold nanocages (AuHNCs) as an effective electrocatalyst is evaluated for electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The electrochemical experiments are carried out at various potentials in 0.5M LiClO4 aqueous solution using AuHNCs, and their catalytic efficiency is determined for the conversion of nitrogen to ammonia [1, 2]. The highest ammonia Faradaic efficiency (30.2%) is achieved at−0.4 V vs. RHE while the highest ammonia yield (3.9 μg cm-2 h-1) is obtained at −0.5 V vs. RHE. The electrocatalytic activity of NRR using AuHNCs is further compared with that of solid Au nanoparticles of various shapes (i.e., rods, spheres or cubes) to elucidate the enhanced rate of the reaction resulting from the increase in surface area and confinement effects. The three-fold enhancement in ammonia Faradaic efficiency is achieved by using the AuHNCs (30.2%) compared to the solid Au nanocubes (11.4%) [1]. It has been demonstrated that electrochemical N2 reduction for NH3 production using Pd nanoparticles requires lower overpotential and results in higher electrocatalytic efficiency for NH3 compared with Au nanoparticles. The use of Pd and hybrid Au-Pd nanoparticles is evaluated for electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The results are further complemented by in-situ surface-enhanced Raman spectroscopy (SERS) and ex-situ 1H NMR to monitor the trace amount of NH3 over the course of the experiment and elucidate the possible differences in the reaction mechanism for electrosynthesis of NH3 on Pd and Au surfaces.

Resonant-XRD Characterization of Nanoalloyed Au-Pd Catalysts for the Direct Synthesis of H2O2: Quantitative Analysis of Size Dependent Composition of the Nanoparticles †

The focus of this work is on the relationship between the quantitative structural characterization of bimetallic Au-Pd nanoparticles dispersed in an amorphous polymer matrix and their catalytic activity in the direct synthesis of hydrogen peroxide (DS reaction). Resonant X-ray powder diffraction with synchrotron radiation was employed to probe selectively and to reveal fine details of the structure of bimetallic nanoparticles embedded in the support. The semi-quantitative analysis of the resonant X-ray powdered diffraction data, made on a large number of metal nanoparticles, shows that in one of the polymer-supported Au-Pd catalyst for the DS reaction (P75) featured by an overall molar Pd/Au of about 5.54, the smallest metal nanoparticles (MNPs), which account for more than 99.9% of the total MNPs number and for more than 95% of the metal surface, are formed by practically pure palladium. The relative number of bimetallic alloyed nanoparticles is very small (less than 4 × 102 ppm) and they contribute to only about 2% of the total metal surface. In a second gold-enriched catalyst (P50) with an overall molar Pd/Au of 1.84, the proportion of the bimetallic alloyed nanoparticles increased to about 97% and they account for about 99% of the metal surface. As a result of the metal intermixing, the catalytic productivity for the DS reaction increased from 97 to 109 mmolH2O2/molH2, owing to the gold-promotion of palladium.

Structural and electronic feature evolution of Au-Pd bimetallic catalysts supported on graphene and SiO2 in H2 and O2

The structure and electronic feature evolution of graphene (Gr)- and SiO2-supported Au-Pd bimetallic nanoparticles (NPs) in H2 and O2 at different temperatures were investigated with a series of techniques and DFT calculation method. It was found that a uniform Au-Pd alloy nanostructure was formed on Gr, while a Au@Pd core-shell structure was generated on SiO2. The formation of Au-Pd alloy nanostructure on Gr originates from a strong s-p-d hybridization among Au 5d6s, Pd 4d and Gr C 2p, which greatly facilitates the electron transfer among Au, Pd and Gr and enhances the reduction of palladium species. The higher stability of the geometric and electronic structures of Au-Pd NPs on Gr than on SiO2 in both H2 and O2 atmospheres below 100 °C results from the fact that Gr could timely supplement the electrons transferring to O2 from metallic species in O2-treatment process, but play a contrary role in H2-treatment process. Such unique geometric and electronic structures endow Au-Pd/Gr show higher catalytic activity than Au-Pd/SiO2 in selective oxidation of methanol to methyl formate. A further investigation of catalytic mechanism reveals that the activation of O2 is dominated by the methanol-assisted way on Au and Au-Pd alloy NPs, whereas the direct dissociation of O2 mainly occurs on Pd and Au@Pd NPs.