AuPd Nanocatalysts Research Articles

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.

Enhanced Hot Electron Flow and Catalytic Synergy by Engineering Core-Shell Structures on Au-Pd Nanocatalysts.

The synergistic catalytic performances of bimetallic catalysts are often attributed to the reaction mechanism associated with the alloying process of the catalytic metals. Chemically induced hot electron flux is strongly correlated with catalytic activity, and the interference between two metals at the atomic level can have a huge impact on the hot electron generation on the bimetallic catalysts. In this study, we investigate the correlation between catalytic synergy and hot electron chemistry driven by the electron coupling effect using a model system of Au-Pd bimetallic nanoparticles. We show that the bimetallic nanocatalysts exhibit enhanced catalytic activity under the hydrogen oxidation reaction compared with that of monometallic Pd nanocatalysts. Analysis of the hot electron flux generated in each system revealed the formation of Au/PdOx interfaces, resulting in high reactivity on the bimetallic catalyst. In further experiments with engineering the Au@Pd core-shell structures, we reveal that the hot electron flux, when the topmost surface Pd atoms were less affected by inner Au, due to the concrete shell, was smaller than the alloyed one. The alloyed bimetallic catalyst forming the metal-oxide interfaces has a more direct effect on the hot electron chemistry, as well as on the catalytic reactivity. The great significance of this study is in the confirmation that the change in the hot electron formation rate with the metal-oxide interfaces can be observed by shell engineering of nanocatalysts.

AuPd Nanocatalysts Supported on Citric Acid-Modified Boron Nitride to Boost Hydrogen Generation from Formic Acid Dehydrogenation

Formic acid (FA) dehydrogenation is a potential technology for sustainable hydrogen production, while the tardy nature of FA dehydrogenation inhibits its development. To optimize the catalytic activity of hydrogen generation from formic acid dehydrogenation, citric acid-modified boron nitride with abundant −NH2 (CA–BN-NH2) is employed as a support to control the particle distribution, particle size, and electronic structure of AuPd nanoparticles. The obtained Au0.3Pd0.7/CA–BN-NH2 exhibits extraordinary catalytic activity for hydrogen production from FA dehydrogenation, possessing 100% hydrogen selectivity and an unprecedented initial turnover frequency (TOF) of 7046 mol H2 mol catalyst–1 h–1 without any additive, outperforming most of the reported noble metal catalysts under similar conditions. Transmission electron microscopy (TEM) images, X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations demonstrate that the extraordinary catalytic activities are mainly due to the geometric effect and electronic effect of AuPd nanoparticles derived from the modification of h-BN with citric acid and the accompanying −NH2. This work provides more flexibility for designing highly efficient nanocatalysts for hydrogen generation from FA dehydrogenation.

Mechanistic Studies into the Selective Production of 2,5-furandicarboxylic Acid from 2,5-bis(hydroxymethyl)furan Using Au-Pd Bimetallic Catalyst Supported on Nitrated Carbon Material

Aerobic oxidation of bio-sourced 2,5-bis(hydroxymethyl)furan (BHMF) to 2, 5-furandicarboxylic acid (FDCA), a renewable and green alternative to petroleum-derived terephthalic acid (TPA), is of great significance in green chemicals production. Herein, hierarchical porous bowl-like nitrogen-rich (nitrated) carbon-supported bimetallic Au-Pd nanocatalysts (AumPdn/ N-BNxC) with different nitrogen content and bimetal nanoparticle sizes were developed and employed for the highly efficient aerobic oxidation of BHMF to FDCA in sodium carbonate aqueous solution. The reaction pathway for catalytic oxidation of BHMF went through the steps of BHMF→HMF→HMFCA→FFCA→FDCA. Kinetics studies showed that the activation energies of BHMF, HMF, HMFCA, and FFCA were 58.1 kJ·moL−1, 39.1 kJ·moL−1, 129.2 kJ·moL−1, and 56.3 kJ·moL−1, respectively, indicating that the oxidation of intermediate HMFCA to FFCA was the rate-determining step. ESR tests proved that the active species was a superoxide radical. Owing to the synergy between the nitrogen-rich carbon support and bimetallic Au-Pd nanoparticles, the Au1Pd1/N-BN2C nanocatalysts exhibited BHMF conversion of 100% and FDCA yield of 95.8% under optimal reaction conditions. Furthermore, the nanocatalysts showed good stability and reusability. This work provides a versatile strategy for the design of heterogeneous catalysts for the highly efficient production of FDCA from BHMF.

Hydrogen Generation from Formic Acid Boosted by Functionalized Graphene Supported AuPd Nanocatalysts

Hydrogen Generation from Formic Acid Boosted by Functionalized Graphene Supported AuPd Nanocatalysts

Unlocking synergy in bimetallic catalysts by core-shell design.

Extending the toolbox from mono- to bimetallic catalysts is key in realizing efficient chemical processes1. Traditionally, the performance of bimetallic catalysts featuring one active and one selective metal is optimized by varying the metal composition1-3, often resulting in a compromise between the catalytic properties of the two metals4-6. Here we show that by designing the atomic distribution of bimetallic Au-Pd nanocatalysts, we obtain a synergistic catalytic performance in the industrially relevant selective hydrogenation of butadiene. Our single-crystalline Au-core Pd-shell nanorods were up to 50 times more active than their alloyed and monometallic counterparts, while retaining high selectivity. We find a shell-thickness-dependent catalytic activity, indicating that not only the nature of the surface but also several subsurface layers play a crucial role in the catalytic performance, and rationalize this finding using density functional theory calculations. Our results open up an alternative avenue for the structural design of bimetallic catalysts.

Mechanism and Kinetics of Methane Oxidation to Methanol Catalyzed by AuPd Nanocatalysts at Low Temperature

The selective oxidation of methane to methanol at ambient conditions has the potential to enable the use of natural gas obtained in remote areas. We performed multivariate statistical analysis of 1...

Decomposition of Hydrogen Peroxide Catalyzed by AuPd Nanocatalysts during Methane Oxidation to Methanol

Selective oxidation of methane into energy-dense liquid derivatives at low temperature and pressure is critical for enabling the use of vast natural gas reserves around the world. This has been rec...

Au–Pd Nanostars with Low Pd Content: Controllable Preparation and Remarkable Performance in Catalysis

Bimetallic nanoparticles consisting of gold (Au) and palladium (Pd) have attracted considerable attention because of their effective catalysis for many chemical reactions. They are highly expected to help in the preparation of Au–Pd nanocatalysts with a controllable structure, morphology, and composition. Here, we show that Au–Pd nanostars (NSs) with tunable surface plasmon resonance absorption (from 536 to 583 nm), nanoparticle size, and palladium content (less than 7 wt %) can be obtained by adjusting the ratio of ascorbic acid and chloroauric acid. These synthesized Au–Pd NSs could be utilized efficiently for the reduction of 4-nitrophenol and nitrobenzene and the Suzuki coupling reaction. Their enhanced catalytic activity could be due to their easy accessibility of the active sites, star-like structure, and Pd-rich surface. The systematic synthesis reported in this work will not only give researchers new insights into the controllable preparation of bimetallic nanoparticles but may also inspire further studies of multifunctional nanocatalysts.

Integrating bimetallic AuPd nanocatalysts with a 2D aza-fused π-conjugated microporous polymer for light-driven benzyl alcohol oxidation

Efficient catalytic system with low energy consumption exhibits increasing importance due to the upcoming energy crisis. Given this situation, it should be an admirable strategy for reducing energy input by effectively utilizing incident solar energy as a heat source during catalytic reactions. Herein, aza-fused π-conjugated microporous polymer (aza-CMP) with broad light absorption and high photothermal conversion efficiency was synthesized and utilized as a support for bimetallic AuPd nanocatalysts in light-driven benzyl alcohol oxidation. The AuPd nanoparticles anchored on aza-CMP (aza-CMP/AuxPdy) exhibited excellent catalytic performance for benzyl alcohol oxidation under 50 mW/cm2 light irradiation. The improved catalytic performance by the aza-CMP/AuxPdy is attributed to the unique photothermal effect induced by aza-CMP, which can promote the catalytic benzyl alcohol oxidation occurring at AuPd. This work presents a novel approach to effectively utilize solar energy for conventional catalytic reactions through photothermal effect.

Ternary CoAuPd and binary AuPd electrocatalysts for methanol oxidation and oxygen reduction reaction: Enhanced catalytic performance by surface reconstruction

Two kinds of ternary cobalt gold palladium (CoAuPd) and three kinds of binary AuPd alloy nanocatalysts are synthesized by co-reduction and successive reduction method. The CoAuPd nanocatalysts obtained by the successive reduction method possess a hollow structure with some solid nanospheres, nanodendrites and show much better catalytic activity for methanol oxidation reaction (MOR) (1.26 mA cm−2) than another CoAuPd NCs (1.14 mA cm−2) and binary AuPd nanocatalysts (0.85 mA cm−2). CO adsorption and electrochemical dealloying method can restructure nanocatalyst surface and improve MOR and oxygen reduction reaction (ORR) activities. Electrochemical dealloying reconstructs the hollow CoAuPd alloy to a CoAuPd@AuPd core-shell structure with pinholes and the dealloyed NCs exhibits better MOR (1.92 mA cm−2) and ORR (6.3 mA cmGEO−2) catalytic activities than the initial CoAuPd nanocatalysts (1.26 mA cm−2 for MOR and 3.4 mAcmGEO−2 for ORR). Accelerated durability tests (ADT) quantify the changes of stability before and after the surface reconstruction. The ternary CoAuPd nanocatalysts have excellent durability before and after surface reconstruction (current density decrease 14.04% for MOR and 0.3 mA cmGEO−2 for ORR) in alkaline medium.

Ab initio studies of ethanol dehydrogenation at binary AuPd nanocatalysts

Density Functional Theory (DFT) simulations have been performed to study ethanol anaerobic oxidation at 10-atom binary gold–palladium clusters with varying compositions, ranging from 0% to 100% gold content. For each case, we have studied the loss of two hydrogen atoms, the desorption of acetaldehyde, and recombination of hydrogen into gas-phase H2. The results show that alloying produces sizable changes in the reaction barriers and in the stability of the intermediate species, which are related to different intrinsic reactivities of palladium and gold.

Fingerprint Feature of Atomic Intermixing in Supported AuPd Nanocatalysts Probed by X-ray Absorption Fine Structure

We report on a systematic study of AuPd bimetallic nanoparticles (NPs) prepared from two-step sputtering deposition in the suspension of graphene and ionic liquid using X-ray absorption fine structure (XAFS) spectroscopy. As-synthesized AuPd bimetallic catalysts possess well-enhanced activity and stability compared with monometallic (Au-only or Pd-only) catalysts, suggesting the synergistic effect upon alloying. A structural model with the introduction of Pd to Au cluster is provided to study the formation of bimetallic NPs and to offer detailed insights into the local structure information (interaction between Au and Pd). A novel and significant fingerprint is proposed to depict the intermixing structure of AuPd bimetallic NPs. The present XAFS study reveals a fingerprint feature in k-space, which can be an evaluation of the extent of the Au–Pd intermixing on the atomic scale, corresponding to the catalytic activity of bimetallic nanoparticles. The systematic XAFS-based methodology, demonstrated here on ...

Sub 1 nm aggregation-free AuPd nanocatalysts confined inside amino-functionalized organosilica nanotubes for visible-light-driven hydrogen evolution from formaldehyde

Novel amino-functionalized organosilica nanotubes (AM-NT) were facilely synthesized by the hydrolysis and co-condensation of 3-aminopropyltrimethoxysilane (APTMS) with 1,4-bis(triethoxysilyl)benzene (BTEB) using a simple micelle-templating approach. Through adjusting the ratios of organosilane precursors, the very short AM-NT with ∼60nm in length and ∼6nm in pore diameter could be controllably obtained. By using the unique AM-NT as the supports, a series of AuPd alloy nanoparticles with the average size of sub 1nm could be synthesized after the liquid phase reduction of HAuCl4 and H2PdCl4 in water, which were mostly confined inside the short organosilica nanotubes and further applied for the hydrogen evolution from formaldehyde aqueous solution. These bimetallic AuPd nanocatalysts in the organic-modified nanotubes exhibited remarkably improved catalytic activity under visible light irradiation and the highest initial TOF value of 241.7h−1 could be achieved at the room temperature. Furthermore, these ultrasmall nanocatalysts exhibited high reaction stability and no aggregation of metal nanoparticles was observed even after 5 recycles. The superior catalytic activity was mainly attributed to the uniform and ultrafine AuPd nanostructure, benefiting from the synergetic stabilizing effects of amino and benzene groups in the nanotube frameworks. The fast electron transfer from much smaller Au with localized surface plasmon resonance (LSPR) to active Pd sites could efficiently occur, resulting in the excellent photocatalytic activity.

Catalytic performance of cobalt oxide-supported gold-palladium nanocatalysts for the removal of toluene and o-xylene

Using the molten salt and polyvinyl alcohol-protected reduction method, we fabricated Co3O4 octahedron-supported Au-Pd (x(AuPdy)/Co3O4; x = (0.18, 0.47, and 0.96) wt%; y (Pd/Au molar ratio) = 1.85−1.97) nanocatalysts. The molten salt-derived Co3O4 sample possessed well-defined octahedral morphology, with an edge length of 300 nm. The Au-Pd nanoparticles, with sizes of 2.7−3.2 nm, were uniformly dispersed on the surface of Co3O4. The 0.96 (AuPd1.92)/Co3O4 sample showed the highest catalytic activity for toluene and o-xylene oxidation, and the temperature required for achieving 90% conversion of toluene and o-xylene was 180 and 187 °C, respectively, at a space velocity of 40000 mL/(g–h). The high catalytic performance of Co3O4 octahedron-supported Au-Pd nanocatalysts was associated with the interaction between Au-Pd nanoparticles and Co3O4 and high concentration of adsorbed oxygen species.

Au-Rh and Au-Pd nanocatalysts supported on rutile titania nanorods: structure and chemical stability.

Au, Rh, Pd, Au-Rh and Au-Pd nanoparticles (NPs) were synthesized by colloidal chemical reduction and immobilized on hydrothermally-prepared rutile titania nanorods. The catalysts were characterized by aberration-corrected TEM/STEM, XPS, and FTIR, and were evaluated in the hydrogenation of tetralin in the presence of H2S. Oxidizing and reducing thermal treatments were employed to remove the polyvinyl alcohol (PVA) surfactant. Reduction in H2 at 350 °C was found efficient for removing the PVA while preserving the size (ca. 3 nm), shape and bimetallic nature of the NPs. While Au-Pd NPs are alloyed at the atomic scale, Au-Rh NPs contain randomly distributed single-phase domains. Calcination-reduction of Au-Rh NPs mostly leads to separated Au and Rh NPs, while pre-reduction generates a well-defined segregated structure with Rh located at the interface between Au and TiO2 and possibly present around the NPs as a thin overlayer. Both the titania support and gold increase the resistance of Rh and Pd to oxidation. Furthermore, although detrimental to tetralin hydrogenation initial activity, gold stabilizes the NPs against surface sulfidation in the presence of 50 ppm H2S, leading to increased catalytic performances of the Au-Rh and Au-Pd systems as compared to their Rh and Pd counterparts.

Au–Pd/3DOM Co3O4: Highly active and stable nanocatalysts for toluene oxidation

The polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction routes were adopted to prepared three-dimensionally ordered macroporous (3DOM) Co3O4 and its supported gold–palladium alloy (xAuPd/3DOM Co3O4, x=0.50–1.99wt% and Au/Pd mass ratio=1:1) nanocatalysts. The 3DOM Co3O4 supported Au–Pd samples performed much better than supported single Au or Pd samples, with the 1.99AuPd/3DOM Co3O4 sample showing the best performance: the T10%, T50%, and T90% (temperatures required for achieving toluene conversions of 10%, 50%, and 90%) were 145, 164, and 168°C at a space velocity of 40,000mL/(gh), respectively. The 3DOM Co3O4 supported Au–Pd nanocatalysts also exhibited better catalytic stability and more moisture-tolerant ability than the supported Au or Pd samples for toluene oxidation. The apparent activation energies (33–41kJ/mol) over xAuPd/3DOM Co3O4 were much lower than those (52–112kJ/mol) over 3DOM Co3O4 and supported single Au or Pd samples, with the 1.99AuPd/3DOM Co3O4 sample exhibiting the lowest apparent activation energy (33kJ/mol). It is concluded that better oxygen activation ability and stronger noble metal–3DOM Co3O4 interaction were responsible for the excellent catalytic performance of 1.99AuPd/3DOM Co3O4.