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We use CeO x -TiO2 hetero-interfaces generated on the surface of CeO x -TiO2 hybrid oxide supporting powders to stabilize Au single-atoms (SAs) with excellent low-temperature activity toward CO oxidation. Based on intriguing density functional theory calculation results on the preferential formation of Au-SAs at the CeO x -TiO2 interfaces and the high activity of Au-SAs toward the Marsâ€"van Krevelen type CO oxidation, we synthesized a Au/CeO x -TiO2 (ACT) catalyst with 0.05 wt.% of Au content. The Au-SAs stabilized at the CeO x -TiO2 interfaces by electronic coupling between Au and Ce showed improved low-temperature CO oxidation activity than the conventional Au/TiO2 control group catalyst. However, the light-off profile of ACT showed that the early activated Au-SAs are not vigorously participating in CO oxidation. The large portion of the positive effect on the overall catalytic activity from the low activation energy barrier of ACT was retarded by the negative impact from the decreasing active site density at high temperatures. We anticipate that the low-temperature activity and high-temperature stability of Au-SAs that stand against each other can be optimized by controlling the electronic coupling strength between Au-SAs and oxide clusters at the Au-oxide-TiO2 interfaces. Our results show that atomic-precision interface modulation could fine-tune the catalytic activity and stability of Au-SAs. [ABSTRACT FROM AUTHOR]

Nanozymes are nanostructured artificial enzymes that have attracted great attention among researchers because of their ability to mimic relevant biological reactions carried out by their natural counterparts, but with the capability to overcome natural enzymes' drawbacks such as low thermostability or narrow substrate scope. The promising enzyme-like properties of these systems make nanozymes excellent candidates for innovative solutions in different scientific fields such as analytical chemistry, catalysis or medicine. Thus, nanozymes with different type of activities are of special interest owing to their versatility since they can reproduce several biological reactions according to the substrates and the environmental conditions. In this context, gold-based nanozymes are a representative example of multifunctional structures that can perform a great number of enzyme-like activities. In addition, the combination of gold-based materials with structures of organic and inorganic chemical nature yields even more powerful hybrid nanozymes, which enhance their activity by providing improved features. This review will carry out a deep insight into gold-based nanozymes, revisiting not only the different type of biological enzymatic reactions that can be achieved with these kinds of systems, but also structural features of some of the most relevant hybrid gold-based nanozymes described in the literature. This literature review will also provide a representative picture of the potential of these structures to solve future technological challenges. [ABSTRACT FROM AUTHOR]

Pure Sa,S and Ra,S atropoisomeric Au(I)- and Au(III)-NHC-complexes with benzimidazolyl N-(2-naphthamide) frameworks were prepared from appropriate axially chiral pre-ligands. The catalytic capacity of gold-NHC-N-naphthyl complexes was studied in cyclopropanation reactions. In contrast to corresponding unsuccessful Au(I)-NHC-N-naphthyl-oxazolyl complexes, all tested Sa,S and Ra,S diastereomers of Au(I) and Au(III)-NHC-N-naphthamide complexes were excellent catalysts to give both successful cyclopropanation (up to 99%, 15 min), as well as subsequent rapid in situ cis-to-trans isomerization. The results demonstrate that the new axially chiral Au(I)-/Au(III)-NHC-benzimidazolyl-N-naphthamide complexes represent an interesting group of gold catalysts with specific properties, affording fast cyclopropanation, excellent product yields and predictable trans-stereoselectivity (>99% yield; >99% trans in 15 min). [ABSTRACT FROM AUTHOR]

Background: The sustainable conversion of biomass‐derived glycerin into high‐value‐added chemicals is a significant challenge in contemporary science. In this context, the selective oxidation of aqueous glycerin into glyceric acid was investigated in the presence of NaOH and atmospheric oxygen. It was demonstrated that the selective transformation of glycerin to glyceric acid involves a new chemical reaction path for commodity glyceric acid that is both abundant and economical. Results: The hydrotalcite‐supported Au nanoparticle catalyst (5%Au/HT) was found to be the most active for glycerin selective transformation to glyceric acid, showing 89.5% glycerin conversion with 61.2% glyceric acid selectivity under optimum experimental conditions. Furthermore, the 5%Au/HT catalyst was reused six times and maintained nearly the same activity in the catalytic recycle experiments. Conclusion: In the Au‐based catalysts, there are strong electronic interactions between the different supports and Au nanoparticles (Au NPs). Besides, the basic sites of the catalysts participated in promotion of hydroxyl functional groups. © 2022 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Three common types of reversible inhibitors, namely competitive, noncompetitive and uncompetitive inhibitors, were designed and constructed by using enzymes with different surface charges and gold nanoparticles with different surface ligands and particle sizes. To our knowledge, it is the first time that an uncompetitive nano inhibitor has been discovered. [ABSTRACT FROM AUTHOR]

Spatial control of reactivity is intrinsically difficult in gold catalysis due to the linear coordination mode of Au(I) and the commonly flat ligands employed for Au(III) complexes. Our recent report of a novel and sterically encumbered (NNN)diiPrAu−OH complex (Eur. J. Inorg. Chem. 2021, 3561–3564.) suggested that the (NNN) ligand framework is capable of sterically interacting with substrates through its conveniently oriented aryl groups. We have now examined these steric properties in more detail by varying the ortho‐substituent of the aryl group in (NNN)xAu−Cl complexes. With just small modifications we were able to vary the buried volume around the Cl atom and correlate this to yields obtained in a Au‐catalyzed Overman rearrangement. Computationally we further elucidate that the stark difference in yields obtained originates from a shift in binding mode of the substrate to the Au catalyst in the rate limiting step of the reaction. We thus conclude that delicate spatial control can be exercised in gold catalysis and propose the (NNN) ligand framework to be an attractive platform for the efficient design of Au(III) complexes for stereoselective catalysis. [ABSTRACT FROM AUTHOR]

A series of Aux/TiO2 nanoparticles (NPs) with different gold loadings (x = 0.1–1.0 wt%) was synthesized by the photodeposition and then employed as photocatalysts to recover precious component from the industrial gold-cyanide plating wastewater. Effects of Au loading, catalyst dosage and types of hole scavenger on the photocatalytic gold recovery were investigated under ultraviolet–visible (UV–Vis) light irradiation at room temperature. It was found that different Au loadings tuned the light absorption capacity of the synthesized photocatalysts and enhanced the photocatalytic activity in comparison with the bare TiO2 NPs. The addition of CH3OH, C2H5OH, C3H8O, and Na2S2O3 as a hole scavenger significantly promoted the photocatalytic activity of the gold recovery, while the H2O2 did not. Among different hole scavengers employed in this work, the CH3OH exhibited the highest capability to promote the photocatalytic gold recovery. In summary, the Au0.5/TiO2 NPs exhibited the best photocatalytic activity to completely recover gold ions within 30 min at the catalyst dosage of 0.5 g/L, light intensity of 3.20 mW/cm2 in the presence of 20 vol% CH3OH as hole scavenger. The photocatalytic activity slightly decreased after the 5th cycle of recovery process, indicating its high reusability. [ABSTRACT FROM AUTHOR]

Gold catalysts possess the advantages of water and oxygen resistance, with the possibility of catalyzing many novel chemical transformations, especially in the syntheses of small-molecule skeletons, in addition to achieving the rapid construction of multiple chemical bonds and ring systems in one step. In this feature paper, we summarize recent advances in the construction of small-molecule scaffolds, such as benzene, cyclopentene, furan, and pyran, based on gold-catalyzed cyclization of arylalkyne derivatives within the last decade. We hope that this review will serve as a useful reference for chemists to apply gold-catalyzed strategies to the syntheses of related natural products and active molecules, hopefully providing useful guidance for the exploration of additional novel gold-catalyzed approaches. [ABSTRACT FROM AUTHOR]

Gold catalysis is an extremely enthusiastic field of investigation in the catalysis area. The development of alternative, highly inventive, precompetitive techniques based on gold catalysis has paved the way for executing a broad spectrum of chemical transformations from uncomplicated starting materials. The total synthesis of natural products is a complex and more complicated task. An amalgamation of natural product synthesis through gold‐catalysis has been a thought‐provoking job. The protocol has solved several problems related to the synthesis of numerous complicated natural products. Thus, this review has outlined some of the most notable benchmarks from the last seven years (2015–2021) on gold catalysis and their application in the total synthesis of numerous natural products. The strategy acquired by the authors to accomplish the total synthesis will be elaborately discussed by emphasizing the role of the gold‐catalyzed reactions. [ABSTRACT FROM AUTHOR]

Chemical transformation of polyaromatic hydrocarbon (PAH) molecules following different reaction strategies has always been the focus of organic synthesis. In this work, we report the synthesis of a PAH molecule, formation of which consists of an unusual C−C bond cleavage accompanied by a complex π‐conjugated molecular scaffold rearrangement. We demonstrate that the complex chemical transformation is steered by concerted motion of individual Au0 gold atoms on a supporting Au(111) surface. This observation underpins the importance of single‐atom catalysis mediated by adatoms in on‐surface synthesis as well as catalytic activity of single Au0 atoms facilitating cleavage of covalent carbon bonds. [ABSTRACT FROM AUTHOR]

Gold catalysts exhibit poor compatibility with cellular components. We show that encapsulation of a gold catalyst within the cavity of a supramolecular cage improves the reactivity of the gold complex under biological conditions. The gold complex catalyzes an intramolecular hydroarylation to produce a fluorescent dye. The encapsulated gold is able to produce this dye in higher yields compared to the free gold under aqueous aerobic conditions and in the presence of biological additives. The substrate was found to be highly cytotoxic, meaning that a very low substrate concentration of 1 μM is required to carry its transformation inside living cells; however, catalysis in cell culture media carried out at micromolar range is found to be inhibited. Although this specific reaction cannot be applied inside living cells, we present a viable strategy to improve the reactivity of gold catalysts in vivo. [ABSTRACT FROM AUTHOR]

Expensive gold‐based catalysts are frequently used for electrochemical CO2 reduction into CO. A feasible approach to obtain low‐cost Au‐based catalysts is needed. Herein, a novel framework 1 assembled from [Zr48Ni6] nano‐cages is prepared. It exhibits a high BET surface area of 1569 m2 g−1 and high solvents/pH stability. 1 can not only selectively extract AuCl4− from artificial electronic waste, but can then be transformed into low‐cost catalyst Au nanoparticle@1‐x (Au NPs@1‐x, x=1, 2, 3, 4) with tuneable Au NPs sizes. The CO2RR investigations revealed that the Au NPs@1‐3 displayed an excellent FECO of 95.2 % with a current density of 102.9 mA cm−2 at −1.1 V, and such high catalytic activity can be maintained for at least 15 h without obvious decrease because the confinement effect of [Zr48Ni6] nano‐cages prevents Au NPs agglomeration. This work offers a facile strategy to obtain low‐cost and high‐performance Au‐based catalysts for various reactions activated by Au. [ABSTRACT FROM AUTHOR]

[Display omitted] The classical strong metal-support interaction (SMSI) plays a key role in improving thermal stability for supported Au catalysts. However, it always decreases the catalytic activity because of the encapsulation of Au species by support. Herein, we demonstrate that Al3+ is a functional additive which could effectively improve both catalytic activity and sintering resistant property for H 2 pretreated Al3+ doped CeO 2 supported Au (AuCeAl) catalyst at high temperature. The physical characterization and in-situ DRIFTS results provide insight that more oxygen vacancies generated by Al3+ doping could be as preferential adsorption sites for CO molecules when the encapsulation of Au species occurred, which is certificated by an accelerated formation of bicarbonate species. In the meantime, smaller Au nanoparticles with higher dispersion (2.8 nm, 85.63%) is achieved in AuCeAl catalysts, compared with that in CeO 2 supported Au (AuCe) catalysts (5.1 nm, 36.17%). Additionally, the as-prepared AuCeAl catalysts also have superior catalytic performance even after calcination at 800 °C in air. [ABSTRACT FROM AUTHOR]

A series of γ-Al 2 O 3 supported gold-palladium (Au-Pd) alloy nanoparticles (NPs) catalysts were synthesized by a one-pot approach applying mercapto-propyl-trimethoxysilane (MPTMS) as an anchoring ligand. Homogeneously dispersed Au-Pd alloy NPs were observed on the prepared catalysts and their catalytic performance in benzyl alcohol partial oxidation was investigated. Results showed that the highest benzaldehyde yield was achieved on catalyst Au-Pd/7%MPTMS-γ-Al 2 O 3 with a benzaldehyde selectivity of 90%. By establishing the structure-performance relationship, the high activity of catalysts with MPTMS modification was attributed to the anchoring and dispersion effect of MPTMS on Au-Pd NPs, while the high benzaldehyde selectivity was due to the formation of more surface Lewis acid sites after introducing MPTMS, protecting the benzaldehyde from over-oxidation to byproducts. [Display omitted] • The presence of MPTMS led to well-dispersed Au-Pd alloy nanoparticles on alumina support. • The introduction of MPTMS produced more surface Lewis acid sites. • Lewis acid sites interacted with benzaldehyde, inhibiting over-oxidation and achieving high benzaldehyde selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] Since transition-metal-catalyzed reactions are one of the most powerful and direct approaches for the synthesis of organic molecules, translating them to biological systems for biomedical applications is an emerging field. The manipulation of transition metal reactions in biological settings for uncaging prodrugs and synthesizing bioactive drugs has been widely studied. To expand the toolbox of transition-metal-mediated prodrug strategy, this work introduces the 2′-alkynl-biphenylamine precursors for the synthesis of phenanthridine derivatives using a water-compatible gold-catalyzed hydroamination under mild conditions. Moreover, the structure–reactivity relationship revealed that the nucleophilicity of the amine group in the precursor was critical for facilitating the gold-catalyzed synthesis of phenanthridine derivatives. The research shows the potential to be used for phenanthridine-based prodrug designs in an aqueous solution. [ABSTRACT FROM AUTHOR]

• Density functional theory calculations of adsorption energies of CO on gold surfaces and surface edges. • Minimum energy paths show that adsorption energies don't capture the nuances of mechanisms. • The lowest barriers are seen on the (311)/(311) edge. Localized surface plasmons (LSP) on faceted surfaces of gold nanoparticles enable carbon monoxide disproportionation to be driven at room temperature. In order to expand the known surfaces that catalyze this reaction, we explore the adsorption of carbon monoxide at top, long bridge, short bridge, and hole sites on gold (100), (110), (111), (211), and (311) faceted surfaces, as well as the reaction barriers for disproportionation at the lowest energy adsorption site on each surface and edges between two (311) surfaces and (100) and (110) surfaces. Generally, the less atomically dense, higher index facets promote both good adsorption and reactivity, and the edges show lower barriers for disproportionation. For most of the explored surfaces, adsorption directly on top of a gold atom is most favorable. The lowest activation energy for carbon monoxide disproportionation to amorphous carbon and carbon dioxide is predicted for two carbon monoxides adsorbed on top of atoms on the (311)/(311) edge. [Display omitted] [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass upgrading is a pivotal axis in the transition from an economy based on fossil resources to one reliant on renewable biomass resources. Within this context, low-cost Zr-doped MgAl-LDH@Aunano-catalysts are reported in this study as efficient catalysts to synthesize bio-based succinic acid. A series of Zr-doped MgAl-LDH and Au/Zr-doped MgAl-LDH catalysts have been successfully prepared. All catalysts have a lamellar double hydroxide structure LDH even after enrichment with Zr and addition of Au.Au NPs have small average sizes ranging from 1.2 to 8.5 nm. The materials under study showed exalted catalytic performances in the direct synthesis of succinic acid from bio based furfural via an aqueous phase oxidation reaction with H 2 O 2. 84 % of furfural conversion and 99 % selectivity towards succinic acid were achieved.A positive synergy between Zr and Au NPs is highlighted and related to this catalytic performances improvement. [Display omitted] • Efficient Zr-doped MgAl-LDH@Au nano-catalysts for synthesizing bio-based succinic acid. • Au Nps have small average sizes ranging from 1.2 nm to 8.5 nm. • A positive synergy between Zr and Au NPs is highlighted. • Conversion of 84 % and selectivity of 99 % toward succinic acid were achieved. [ABSTRACT FROM AUTHOR]

In an article published in Advanced Energy Materials, researchers Chang Woo Myung, Youngku Sohn, and their team explore the direct electrochemical Fischer-Tropsch chemistry of C1-C7 hydrocarbons using Au-SrTiO3 catalysts. They demonstrate the production of long-chain hydrocarbon fuels through electrochemistry, utilizing CO2 and H2O. The researchers predict the underlying mechanism at the interface using density functional theory calculations. This innovative conversion process offers potential for sustainable fuel production under ambient conditions. [Extracted from the article]

Direct epoxidation of propylene (C 3 H 6) with hydrogen (H 2) and oxygen (O 2) over Au/TS-1 catalyst was promising way for the synthesis of propylene oxide (PO). However, high selectivity of PO (>95 %) and conversion of C 3 H 6 (>5 %) cannot be achieved at the same time. The industrialization process was severely restricted. In this paper, Au/TS-1 catalysts were synthesized by deposition precipitation method with alkali metal promoter. And alkaline gases and silane coupling post-treatment were performed to promote the catalytic activity. The prepared samples exhibited a much better C 3 H 6 conversion (6.5 %) and PO selectivity (95.1 %) compared with general catalyst using normal synthetic technology. Cs 2 CO 3 was beneficial to increasing Au nanoparticles uptake efficiency. Both NH 3 and triethoxyvinylsilane post-treatment were good for smaller and more uniform loading of Au nanoparticles. The decreasing in surface hydroxyl density effectively alleviated the occurrence of PO ring opening isomerization. The increased hydrophobicity of TS-1 surface was conducive to the rapid desorption of generated PO and significantly increased PO selectivity. Multiple pretreatment was also favorable for extending the lifetime of Au/TS-1 catalyst. [Display omitted] • Multiple pretreatment exhibit better loading of Au nanoparticles both on size and distribution. • Charming C 3 H 6 conversion (6.5 %) and PO selectivity (95.1 %) were obtained. • PO ring opening isomerization or oligomerization was effectively inhibited. • Lifetime of Au/TS-1 catalyst extended obviously after multiple pretreatment. [ABSTRACT FROM AUTHOR]

The reactivity of various Pd ensembles on the Au-Pd(100) alloy catalyst toward CO oxidation was investigated by using density functional theory (DFT). This study was prompted by the search for efficient catalysts operating at low temperature for the CO oxidation reaction that is of primary environmental importance. To this aim, we considered Pd modified Au(100) surfaces including Pd monomers, Pd dimers, second neighboring Pd atoms, and Pd chains in a comparative study of the minimum energy reaction pathways. The effect of dispersion interactions was included in the calculations of the O2 dissociation reaction pathway by using the DFT-D3 scheme. The addition of the dispersion interaction strongly improves the adsorption ability of O2 on the Au-Pd surface but does not affect the activation energy barriers of the Transitions States (TSs). As for O2 to dissociate, it is imperative that the TS has lower activation energy than the O2 desorption energy. DFT-D3 is found to favor, in some cases, O2 dissociation on configurations being identified from uncorrected DFT calculations as inactive. This is the case of the second neighboring Pd configuration for which uncorrected DFT predicts positive Gibbs free energy (ΔG) of the O2 adsorption, therefore an endergonic reaction. With the addition of D3 correction, ΔG becomes negative that reveals a spontaneous O2 adsorption. Among the investigated Au-Pd (100) ensembles, the Pd chain dissociates most easily O2 and highly stabilizes the dissociated O atoms; however, it has an inferior reactivity toward CO oxidation and CO2 formation. Indeed, CO strongly adsorbs on the palladium bridge sites and therefore poisoning the surface Pd chain. By contrast, the second neighboring Pd configuration that shows somewhat lower ability to dissociate O2 turns out to be more reactive in the CO2 formation step. These results evidence the complex effect of Pd ensembles on the CO oxidation reaction. Associative CO oxidation proceeds with high energy barriers on all the considered Pd ensembles and should be excluded, in agreement with experimental observations. [ABSTRACT FROM AUTHOR]

The compatibility between gold(I) catalysts and amine transaminases has been explored to transform racemic propargylic alcohols into enantioenriched allylic amines in a straightforward and selective manner. The synthetic approach consists of a gold(I)‐catalysed Meyer‐Schuster rearrangement of a series of 2‐arylpent‐3‐yn‐2‐ols and a subsequent stereoselective enzyme‐catalysed transamination of the resulting α,β‐unsaturated prochiral ketones. The design of cascade processes involving sequential or concurrent approaches has been studied in our search for ideal reaction conditions to produce the desired amines. Thus, the N‐heterocyclic carbene complex [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]‐[bis(trifluoromethanesulfonyl)‐imide]gold(I) ([Au(IPr)(NTf2)] (A) in aqueous medium was found to be an ideal catalyst, while selective, made‐in‐house and commercial amine transaminases permitted the asymmetric synthesis of both (E)‐4‐arylpent‐3‐en‐2‐amine enantiomers in good isolated yields (53–84%) and excellent stereoselectivities (97 to >99% enantiomeric excess). [ABSTRACT FROM AUTHOR]

Aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a promising alternative route to produce renewable biodegradable plastics, which has stimulated intense interest in recent years. Supported gold catalysts have shown great potential for this reaction, but the selectivity and stability need to be improved. In addition, the requirement for base additives makes the process less effective and sustainable. Herein, highly active and selective Au–Ag bimetallic nanoclusters supported on MgAl-hydrotalcite (HT) were developed for HMF oxidation to FDCA under base-free reaction conditions using molecular oxygen as the oxidant. The presence of small amounts of Ag (0.034–0.065 wt%) in Au25 clusters greatly enhanced the catalytic reaction rates and selectivity for HMF tandem oxidative steps, leading to both high conversion of HMF (>97%) and high yield of FDCA (>95%). Besides, the catalyst stability was also enhanced by the addition of Ag. The characterization results suggested that the substitution of Ag atoms modified the electronic structure of Au while likely maintaining the primary geometry. Thus, a significant synergistic effect could be observed over trace Ag modified Au–Ag bimetallic nanoclusters. The present work provides new insight into the alloying effect, and helps understand highly efficient Au-based catalysts for aerobic oxidation of biomass derived molecules under base-free conditions. [ABSTRACT FROM AUTHOR]

Carbon‐supported Au (Au/AC) has been proven to be one of the most promising catalysts in the field of acetylene hydrochlorination. However, the catalytic performance of conventional Au/AC catalyst is usually limited due to the unsatisfactory dispersion of active Au cation on the surface of the support, carbon deposition, and inevitable reduction to inactive Au nanoparticles. Herein, Au catalysts with highly dispersed Au cation were developed using the complexation of dicarbonyl ligand N‐chlorosuccinimide (NCS) and N‐methylsuccinimide (NMS). The obtained Au−NMS/AC and Au−NCS/AC catalysts with 0.1 wt.% Au loading possessed acetylene conversion of 98 % and 88 % at 180 °C and GHSV (C2H2) of 160 h−1, which were clearly better than that of pristine Au/AC. The characterization results showed that coordination between Au cation and ligands enhanced the dispersion of Au species, suppressed the reduction of Au cation, and reduced the formation of carbon deposits. Density functional theory (DFT) calculations suggest that Au−NMS/AC and Au−NCS/AC catalysts follow a HCl‐preferred concerted addition reaction mechanism with lower reaction energy barrier. This favors the high activity and nuclearity stability of the Au center. This study provides great potential for the use of dicarbonyl ligands on Au‐based catalysts in acetylene hydrochlorination. [ABSTRACT FROM AUTHOR]

The present work highlights the versatility of a TiO2-Al2O3 mixed oxide bearing highly dispersed gold nanoparticles that was applied in the CO oxidation reaction at room temperature. The TiO2, Al2O3, and TiO2-Al2O3 supports were synthesized by the sol–gel method, while gold nanoparticles were added by the deposition–precipitation with urea method using a theoretical Au loading of 2 wt.%. A promotional effect of the TiO2-Al2O3 support on the activity of gold catalysts with respect to TiO2 and Al2O3 was observed; Au/TiO2-Al2O3 showed outstanding CO oxidation, being active from 0 °C and stable throughout a 24-h test. As for the alumina content (5, 10, and 15 wt.%) in TiO2, it improved the textural properties by retarding the crystal growth and anatase–rutile phase transformation of TiO2, suppressing the deposition of carbon on the catalyst surface and stabilizing the Au nanoparticles even at high temperatures. Gold was highly dispersed with nanoparticle sizes ranging from 1 to 2 nm when H2 was used to treat thermally the Au/TiO2-Al2O3, Au/TiO2, and Au/Al2O3 materials. In addition, the XPS technique helped elicit that Au0 and Au1+ boosted their interaction with the TiO2, Al2O3, and TiO2-Al2O3 supports by means of charge transfer, which resulted in outstanding CO oxidation activity from 0 °C. Likewise, the key factors that control the peculiar catalytic performance in the CO oxidation reaction are discussed, which represents a step forward in the versatility behavior of gold catalysts supported on mixed oxide catalysts. [ABSTRACT FROM AUTHOR]

Surface adsorption and dissociation processes can have a decisive impact on the catalytic properties of metal alloys. We have used density functional theory to investigate the adsorption and dissociation of O2 on Cu-skin Cu3Au(111) surface. The calculated results show that the b-f(h)-b adsorption configuration is the most energetically favorable on the Cu-skin Cu3Au(111) surface. For O2 dissociation, there are two thermodynamically favorable dissociation paths. One path is from b-f-b to two O atoms in hcp sites, and the other path is from b-h-b to two O atoms in fcc sites. Moreover, the stability of O2 adsorption is higher and the dissociation energy barrier of the adsorbed O2 is lower as compared to those on the Cu(111) surface. This theoretical work provides valuable guidance for the practical application of Cu-Au alloys as highly efficient CO oxidation catalysts. [ABSTRACT FROM AUTHOR]

Gold catalysts, with different particle sizes ranging from 19 to 556 Å, and supported on SBA-15 mesoporous silica, were prepared by using deposition-precipitation, co-precipitation, and impregnation methods. All samples were characterised by TEM, EXAFS, XPS, XRD, CFR (Continuous Flow Reactor), and TPR. The sample which proved to have the highest activity was characterised by TAP (Temporal Analysis of Products) as well. XPS, wide-angle XRD, EXAFS, and H2-TPR measurements and data analysis confirmed that gold was present as Au0 only on all samples. The size of the Au nanoparticle was determined from TEM measurements and confirmed through wide-angle XRD measurements. EXAFS measurements showed that as the Au-Au coordination number decreased the Au-Au bond length decreased. TEM data analysis revealed a dispersion range from 58% (for the smallest particle size) to 2% (for the highest particle size). For Au particles' sized lower that 60 Å, the Au dispersion was determined using a literature correlation between the dispersion and EXAFS Au-Au coordination number, and was in good agreement with the dispersion data obtained from TEM. The Au dispersion decreased as the particle size increased. CFR experiments validated the relationship between the size of the gold particles in a sample and the sample's catalytic activity towards acetone oxidation. The lowest temperature for the acetone 100% conversion, i.e., 250 °C, was observed over the reduced catalyst sample with the smallest particle size. This sample not only showed the highest catalytic activity towards acetone conversion, but, at the same time, showed high reaction stability, as catalyst lifetime tests, performed for 25 h in a CFR at 270 °C for the as-synthesised sample, and at 220 °C for the reduced sample, have confirmed. TAP (Temporal Analysis of Products) measurements and data analysis confirmed a weak competitive adsorption of acetone and oxygen over the Au/SBA-15 sample. Based on TAP data, a combination of Eley–Rideal and Langmuir–Hinshelwood mechanisms for acetone complete oxidation was proposed. [ABSTRACT FROM AUTHOR]

The electrocatalytic reduction of CO2 to other high value-added chemicals under ambient conditions is a promising and ecofriendly strategy to achieve sustainable carbon recycling. However, the CO2 reduction reaction (CO2RR) is still confronted with a large number of challenges, such as high reaction overpotential and low product selectivity. Therefore, the rapid development of appropriate electrocatalysts is the key to promoting CO2 electroreduction. Over the past few decades, Au-based nanocatalysts have been demonstrated to be promising for the selective CO2RR to CO owing to their low reaction overpotential, good product selectivity, high Faraday efficiency and inhibition of the hydrogen evolution reaction. In this respect, this review first introduces the fundamentals of the electrochemical reduction of CO2 and then focuses on recent accomplishments with respect to Au-based nanocatalysts for CO2RR. The manipulation of various factors, e.g., the nanoporous structure, nanoparticle size, composition, morphology, support and ligand, allows for the identification of several clues for excellent Au-based nanocatalysts. We hope that this review will offer readers some important insights on Au-based catalyst design and provide new ideas for developing robust electrocatalysts. [ABSTRACT FROM AUTHOR]

The nature and local environment of Au single atoms supported and stabilized on four different oxides is studied by means of DFT + U calculations using CO as probe molecule and its stretching frequency, ωe, as a fingerprint of the site where the Au atom is bound. Four oxides are considered, anatase TiO2, tetragonal ZrO2, cubic CeO2, and a perovskite LaFeO3. In this latter case a recently reported experimental study has detected a stretching mode for CO adsorbed on Au1/LaFeO3 of 2215 cm−1, with a large blue shift, ∆ω(CO) = 72 cm−1 with respect to free CO. In order to identify the Au adsorption site that can give rise to this large blue-shift we have considered five cases: (a) Au replacing a lattice cation, (Au)subM; (b) Au replacing a lattice O anion, (Au)subO; (c) Au adsorbed on the surface, (Au)ads; (d) Au bound to an extra O atom on the surface, (AuO)ads, or (e) Au bound to two extra O atoms on the surface, (AuO2)ads. It turns out that the correct reproduction of ∆ω for CO adsorbed on positively charged gold, Auδ+, is challenging for DFT. Therefore, we have performed a comparative study of Auδ+-CO molecular compounds for which ωe(CO) is known experimentally using various kinds of DFT functionals and accurate CCSD and CCSD(T) quantum chemistry methods. Also based on this comparison we propose a tentative assignment for the observed frequency of CO adsorbed on Au1/LaFeO3 single atom catalyst. [ABSTRACT FROM AUTHOR]

Molecular docking is emerging as a frequently applied structure-based virtual technique in the drug design processes. The method could significantly reduce the time required for the development of novel and effective molecules compared to high-throughput screening. However, a major drawback of the docking simulations is the high number of false-positive ligands in the top-ranked solutions. Thus, this work focuses on the optimization of genetic optimization for GOLD, and Glide docking protocols in the active sites of crystallographic acetylcholinesterase proteins, which could be used in the processes of design and optimization of novel acetylcholinesterase inhibitors. The performance of GOLD and Glide was assessed by their ability to reproduce known inhibitor conformations of co-crystallized ligands, and to efficiently detect known active compounds seeded into a decoy set. In addition, ensemble docking and molecular mechanics with generalised Born and surface area solvation (MM/GBSA) recalculations were introduced to observe the alterations in the enrichment factors. The variances in the enrichment values between both docking softwares were significant, considering the weak performance of Glide. In all of the employed crystallographic structures, GOLD 5.3 showed drastically better results. Interestingly, the enrichment factors were not increased after utilizing the ensemble docking simulations and the free binding energy recalculations with MM/GBSA. Overall, it was noted that the application of ChemPLP (GOLD 5.3) scoring function in a single acetylcholinesterase protein structure (PDB: 1Q84) displays the most reliable docking results. The obtained data will be beneficial for future virtual screenings of novel acetylcholinesterase inhibitors. [ABSTRACT FROM AUTHOR]

Purple of Cassius is a pigment based on a gold colloid that has been known for hundreds of years. It has had a profound influence on modern nanoscience. But the origin of the small size of the Au nanoparticles (NPs) and their superior stability remains ambiguous. The experiments and characterization studies discussed here confirmed that SnCl2 functioned not only as a reducing agent but also as an effective surface capping agent through bimetallic Au–Sn bonding. This finding expands the types of Au NP stabilizer from traditional organic examples (e.g., thiolate or phosphine) to metallic examples. The formation of a Au–Sn interface also endows Au NPs with excellent activity and separability for the hydration of alkynes to ketones. [ABSTRACT FROM AUTHOR]

The noble metal nanoparticles have attracted attention due to their excellent catalytic performance for CO oxidation at low temperatures. M-CeO2 (M = Pd, Ag, Au) catalysts with different atomic ratios of M/Ce were deposited via solution combustion method. Among them, 3 at% Pd-CeO2, 5 at% Ag-CeO2 and 1 at% Au-CeO2 catalysts have better catalytic performances. Especially, 5 at% Ag-CeO2 catalyst shows better low-temperature CO oxidation performance. The catalytic activity for CO oxidation follows the follows the following sequence: 5 at% Ag-CeO2 (T50 = 69 °C) > 3 at% Pd-CeO2 (T50 = 99 °C) >1 at% Au-CeO2 (T50 = 115 °C). Meanwhile, the catalysts are characterized by means of powder x-ray diffraction, scanning electron microscope, transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Brunauerâ€"Emmettâ€"Teller and H2-TPR. The characterization results show that the 5 at% Ag-CeO2 catalyst has excellent catalytic activity due to the good dispersion of Ag nanoparticles, the specific surface area of the material, and the reduction catalyst between different valence ions. Moreover, the surface of the catalyst enhances the mutual synergy, effectively promotes the generation of oxygen vacancies, and increases the active oxygen content of the catalyst surface. Finally, the catalytic mechanism of M-CeO2 catalysts is summarized. [ABSTRACT FROM AUTHOR]

Mechanochemistry has proven to be an excellent green synthesis method for preparing organic, pharmaceutical, and inorganic materials. Mechanocatalysis, inducing a catalytic reaction by mechanical forces, is an emerging field because neither external temperature nor pressure inputs are required. Previous studies reported enhanced catalytic activity during the mechanical treatment of supported gold catalysts for CO oxidation. So far, the processes inside the milling vessel during mechanocatalysis could not be monitored. In this work, the results of high‐energy operando X‐ray powder diffraction experiments and online gas analysis will be reported. A specific milling setup with a custom‐made vessel and gas dosing system was developed. To prove the feasibility of the experimental setup for operando diffraction studies during mechanocatalysis, the CO oxidation with Au@Fe2O3 as a catalyst was selected as a well‐known model reaction. The operando studies enabled monitoring morphology changes of the support as well as changes in the crystallite size of the gold catalyst. The change of the crystal size is directly correlated to changes in the active surface area and thus to the CO2 yield. The studies confirm the successful implementation of the operando setup, and its potential to be applied to other catalytic reactions. [ABSTRACT FROM AUTHOR]

Using a modified deposition-precipitation method, a series of Au–Mo/ZSM-5 catalysts with different Au loadings were prepared. The XRD, nitrogen adsorption-desorption, NH3-TPD, and TEM results showed that introducing gold significantly reduced the BET surface area and increased the acid content of the catalyst. The results of the catalytic cracking of light diesel oil showed that the conversion, micro-reactivity index, and propylene selectivity of the 1.0%Au–5%Mo/ZSM-5 catalyst were respectively by 3.59, 3.41, and 16.8% higher than those of ZSM-5. [ABSTRACT FROM AUTHOR]

Alkynes are one of the most important groups of building blocks in organic chemistry as they work as nucleophiles upon deprotonation of its acidic hydrogen. On the surface of a gold catalyst the reactivity of an alkyne towards dehydrogenation depends on the stability of the resulting acetylide species and on its Brønsted acidic behavior with respect to other species in the system. Herein, we study the reaction of alkynes on an oxygen-covered gold surface, hereafter described as O/Au, with and without species able to build acid–base pairs on the surface. As expected, alkynes undergo a facile dehydrogenation process, forming acetylide species and coupling products such as CH3–CC–CC–CH3 from propyne (CH3–CC–H). However, temperature-programmed reactions show that the catalytic intermediates are strongly attached to the surface, leading to parallel decomposition pathways that result in the carbon poisoning of the catalyst. The strong attachment suggests that the alkynes can displace species known to undergo facile dehydrogenation on gold, such as adsorbed alkoxy, as demonstrated by experiments using selected alcohols and alkynes. Moreover, alkynes can even displace alcohols of similar molecular weight (acetylene vs. methanol; phenylacetylene vs. phenol). The results indicate that a gold catalyst facilitates the formation of acetylide species and coupling products, even though their strong interaction with the surface may be counterproductive, as it results in their decomposition. [ABSTRACT FROM AUTHOR]

Heterogeneous catalysts based on metallic nanoparticles are promising candidates for wastewater treatment. However, they aggregate easily as a result of their high surface energy. Polymers are very popular supporting catalyst materials because they can stabilize the metallic nanoparticles to prevent aggregation. In this study, aniline-pentamer-based electroactive polyurea (EPU) was synthesized by oxidative coupling, and Au nanoparticles were anchored to the EPU via its aniline segments. Electrochemical redox behavior of the as-synthesized EPU was monitored by electrochemical cyclic voltammetry. The Au/EPU composite was characterized by FTIR, UV–vis, TGA, SEM, TEM, XRD XPS, and ICP-OES. SEM showed that the EPU had a flower-like structure, and the Au nanoparticles were uniformly immobilized on the EPU surface. The reduction of 4-nitrophenol (4-NP) by NaBH4 was used as a model reaction to evaluate the catalytic properties of the Au/EPU composite. Moreover, the optimization of the reaction conditions for the reduction of 4-NP to 4-aminophenol (4-AP) were also studied in detail. The Au/EPU composite catalyzed the reduction of 4-NP to 4-AP within 4 min with a rate constant of 2.4 × 10–2 s−1 and an activation energy of 40.17 kJ/mol. The Au/EPU composite demonstrated high conversion (98%) after 20 successive cycles. [ABSTRACT FROM AUTHOR]

The efficient SBA-15 supported silver catalysts(Ag/SBA-15) were prepared and characterized by ICP-OES, XRD, TEM, SEM, XPS and N2 adsorption–desorption techniques. The catalysts exhibited an excellent catalytic activity for the aerobic oxidation of toluene to benzaldehyde under solvent-free conditions. Conversion of toluene and selectivity of benzaldehyde were 50% and 89% respectively over catalyst with 9.1 wt% Ag loading (10Ag/SBA-15). A wide range of substrates were tolerated under the selected reaction conditions. The kinetic study shows that the oxidation of toluene over 10Ag/SBA-15 is pseudo-first-order reaction and the activation energy Ea is 45.1 kJ/mol. A plausible mechanism involving oxygen free radicals was proposed for the aerobic oxidation reaction. Compared with the traditional method, the newly designed heterogeneous catalytic system shows better economic applicability, environmental friendliness and broader application prospects. [ABSTRACT FROM AUTHOR]

Inorganic metal (hydro)oxide supports with appropriate basicity or acid‐base properties can promote oxidative esterification of furfural over Au‐based catalysts, however, they suffer the problems of easy inactivation induced by the leaching of the components in this water‐producing reaction and the shield of catalytic sites by product adsorption. In this work, we report efficient and stable oxidative esterification of furfural over Au nanoparticles anchored in aminopropyl‐grafted silica aerogel. The support is insoluble and possesses no strong Lewis acid sites to adsorb oxygen‐containing products or intermediates, reducing the probability of catalyst deactivation induced by adsorption. In 7 cycles of reactions, the catalyst maintained the initial activity without any treatments, the yields of alkyl furoate kept above 98 %, and no agglomeration and leaching of Au occurred. Moreover, the roles of Au, alkyl chain, −NH2 group and Au‐activated O species in reactions were clarified, and accordingly, a possible catalytic mechanism involving oxidative dehydrogenation was given. [ABSTRACT FROM AUTHOR]

Photocatalytic CO2 reduction to CH4 is a promising strategy for converting the main greenhouse gas CO2 to achieve a future with net-zero emissions. However, efficient photocatalysts with high selectivity are still far from being applied. In the present work, we reported BiOCl nanosheets loaded with noble metals (Au, Ag, Pt, or Pd), fabricated via a facile photodeposition method, for photocatalytic CO2 reduction. Among these metals, Pd-loaded BiOCl (Pd/BiOCl) with 1.0 wt% loading showed the highest activity and best selectivity toward CH4 formation. The enhancements in activity and selectivity were further studied by investigating the photogenerated electron–hole separation efficiency and surface intermediate pathways during photocatalytic CO2 reduction. It was found that Pd-loaded BiOCl could effectively decrease the recombination of electrons and holes and improve the photocurrent density during light irradiation. Furthermore, surface CO2 adsorption studies based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) implied that bicarbonates rather than carbonates were the main species on Pd/BiOCl under dark conditions. These species were increased and further transformed to bidentate formate and methoxy as key intermediates during CH4 formation. The enhanced charge separation efficiency and formation of bidentate formate and methoxy on Pd/BiOCl promoted the CH4 activity and selectivity during photocatalytic CO2 reduction. Our work provides a facile and efficient way to achieve photocatalytic CO2 reduction for the selective formation of CH4. [ABSTRACT FROM AUTHOR]

We propose a simple way to synthesize gold catalysts consisting of dominant ca. 2 nm nanoparticles and single atoms on different carbons by the use of L‐arginine‐Au(III) complexes. The decomposition of the precursor proceeds via concurrent anchoring surface amine groups and forming gold species. The gold catalyst supported on a commercial nitrogen free carbon of the Sibunit family showed excellent activity in the gas phase formic acid decomposition reaction and 100 % selectivity towards hydrogen formation as compared to gold catalysts supported on nitrogen free and nitrogen doped carbon nanofibers and nanotubes. The observed increase in the reaction rate by a factor of up to 15 is due to the enrichment of external Sibunit surface with gold and surface amine groups. The intrinsic nitrogen centers of the nitrogen doped carbons are not sensitive to the gold precursor, thus not affecting the dispersion of gold and even deteriorating the catalyst activity. [ABSTRACT FROM AUTHOR]

Bioorthogonal chemistry introduces nonbiogenic reactions that can be performed in biological systems, allowing for the localized release of therapeutic agents. Bioorthogonal catalysts can amplify uncaging reactions for the in situ generation of therapeutics. Embedding these catalysts into a polymeric nanoscaffold can protect and modulate the catalytic activity, improving the performance of the resulting bioorthogonal "polyzymes". Catalysts based on nontoxic metals such as gold(I) are particularly attractive for therapeutic applications. Herein, we optimized the structural components of a metal catalyst to develop an efficient gold(I)-based polyzyme. Tailoring the ligand structure of gold phosphine-based complexes, we improved the affinity between the metal complex and polymer scaffold, resulting in enhanced encapsulation efficiency and catalytic rate of the polyzyme. Our findings show the dependence of the overall polyzyme properties on the structural properties of the encapsulated metal complex. [ABSTRACT FROM AUTHOR]

Two catalytic annulations of non-symmetric diarylketenes with thioalkynes are described using gold and phosphine catalysts respectively. We employed α-aryldiazo ketones to generate gold-π-ketenes, ultimately yielding azulen-1-one derivatives. With the same reactants, we utilized P(C6F5)3 to increase the yields of 1-naphthols, notably with a complete regioselectivity. [ABSTRACT FROM AUTHOR]

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

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol. [ABSTRACT FROM AUTHOR]

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

In the study, the effects of gold catalyst on the thermal decomposition characteristics and thermal safety of methylhydrazine were studied with the differential scanning calorimetry. The kinetic and thermal safety parameters of methylhydrazine with and without gold catalyst were calculated, including apparent activation energy, pre-exponential constant, self-accelerating decomposition temperature, critical temperatures of thermal explosion and adiabatic time to explosion. Thus, entropies of activation, enthalpies of activation and free energies of activation of thermodynamic parameters were also computed. The results showed that the thermal decomposition of methylhydrazine had only one strong exothermic process and the values of apparent activation energy, self-accelerating decomposition temperature and critical temperatures of thermal explosion of methylhydrazine were 159.13 kJ·mol−1, 451.53 K and 469.55 K, respectively. However, these parameters of methylhydrazine with the presence of gold catalyst were 69.03 kJ·mol−1, 361.24 K and 400.22 K, respectively. Non-isothermal kinetics analysis revealed that gold greatly reduced the values of apparent activation energy, self-accelerating decomposition temperature and critical temperatures of thermal explosion of methylhydrazine, leading to an obvious promoting effect on its thermal decomposition. Therefore, gold would significantly decrease the thermal safety of methylhydrazine and increase its explosion risk in a closed system. [ABSTRACT FROM AUTHOR]

This work describes the empirical screening of base types and amounts on the catalytic property of gold‐polymer composite particles in the aerobic homocoupling of arylboronic acid. As these particles notably improve the yields of biaryl in the presence of bases, various bases and their amounts are systematically tested to experimentally identify an ideal base that can provide high reactivity and recyclability of the composite particles in mild and green conditions. Interestingly, the following conditions ‐ soluble strong bases at sub‐stoichiometric quantities (0.5 eq.) and insoluble weak bases at excess amounts (3.0 eq.) in EtOH ‐ significantly enhance the catalytic activities of the composite particles. Upon screening two ideal bases, overall catalytic properties of the composite particles including reaction rate at three different temperatures, activation energy (51–52 kJ/mole), and recyclability (7 cycles) were compared. Understanding the effect of bases and fine‐tuning reaction conditions can potentially improve overall reactivity and recyclability of the composite particles as a green quasi‐homogenous catalyst. [ABSTRACT FROM AUTHOR]

In this work, a new heterogeneous catalyst, comprising gold supported on DABCO-triazole ionic liquid-modified magnetic nanoparticles (Fe3O4@DT-Au), is developed for A3-coupling reaction. This nano-catalyst is characterized using different techniques, such as TEM, SEM, SEM-elemental mapping, XRD, XPS, and TGA. Using a 0.05 mol% of this catalyst, the three-component reaction of amines, aldehydes and alkynes is efficiently performed at 40 °C in water. This catalyst is easily recovered and recycled through external magnetic forces for six times with a small decrease in the activity and re-used catalyst was characterized. [ABSTRACT FROM AUTHOR]

In this study, 3D-structured NiMo coatings have been constructed via the widely used electrodeposition method on a Ti surface and decorated with very small Au crystallites by galvanic displacement (Au(NiMo)/Ti). The catalysts have been characterized using scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma optical emission spectroscopy. Different Au(NiMo)/Ti catalysts, which had Au loadings of 1.8, 2.3, and 3.9 µgAu cm−2, were prepared. The electrocatalytic activity of the Au(NiMo)/Ti catalysts was examined with respect to the oxidation of glucose in alkaline media by cyclic voltammetry. It was found that the Au(NiMo)/Ti catalysts with Au loadings in the range of 1.8 up to 3.9 µgAu cm−2 had a higher activity compared to that of NiMo/Ti. A direct glucose-hydrogen peroxide (C6H12O6-H2O2) single fuel cell was constructed with the different Au-loading-containing Au(NiMo)/Ti catalysts as the anode and Pt as the cathode. The fuel cells exhibited an open circuit voltage of ca. 1.0 V and peak power densities up to 8.75 mW cm−2 at 25 °C. The highest specific peak power densities of 2.24 mW µgAu−1 at 25 °C were attained using the Au(NiMo)/Ti catalyst with the Au loading of 3.9 µg cm−2 as the anode. [ABSTRACT FROM AUTHOR]

Summary: Pt metal is well known for exhibiting superior catalytic activity towards methanol electro‐oxidation process but, it is highly poisoned by the intermediate carbonaceous species (CO) which degrade the catalytic activity over time. In this regard, a noble trimetallic electrode was prepared by modifying an unsupported polycrystalline Pt electrode with a mixture of Au and Co through a simple, one‐step electrochemical deposition technique for investigating the methanol electro‐oxidation (MEO) process in alkaline media. Cyclic voltammetric experiment has revealed that the as‐prepared electrode exhibited more than 50% greater stability than those of polycrystalline Pt ((poly) Pt) and Pt/Au electrodes. Moreover, the ratio of forward MEO oxidation peak current and corresponding backward peak current (If/Ib) was found to be greater for Pt/Au‐Co than (poly) Pt electrode suggesting substantial resistance of the catalyst for CO adsorption. The XPS analysis has demonstrated that Co existed on the electrode surface as Co(II) oxide which is assumed to enhance the stability of Pt/Au‐Co by removing CO species. A relatively smaller Tafel slope (130 mV/dec) was also obtained with Pt/Au‐Co than that of commercially available carbon‐supported Pt catalyst and, the oxidation process was observed to follow half order kinetics concerning methanol. [ABSTRACT FROM AUTHOR]