Au Particles Research Articles

Time-Dependent Size and Shape Evolution of Gold and Europium Nanoparticles from a Bioproducing Microorganism, a Cyanobacterium: A Digitally Supported High-Resolution Image Analysis

Herein, the particle size distributions (PSDs) and shape analysis of in vivo bioproduced particles from aqueous Au3+ and Eu3+ solutions by the cyanobacterium Anabaena sp. are examined in detail at the nanoscale. Generally, biosynthesis is affected by numerous parameters. Therefore, it is challenging to find the key set points for generating tailored nanoparticles (NPs). PSDs and shape analysis of the Au and Eu-NPs were performed with ImageJ using high-resolution transmission electron microscopy (HR-TEM) images. As the HR-TEM image analysis reflects only a fraction of the detected NPs within the cells, additional PSDs of the complete cell were performed to determine the NP count and to evaluate the different accuracies. Furthermore, local PSDs were carried out at five randomly selected locations within a single cell to identify local hotspots or agglomerations. The PSDs show that particle size depends mainly on contact time, while the particle shape is hardly affected. The particles formed are distributed quite evenly within the cells. HR-PSDs for Au-NPs show an average equivalent circular diameter (ECD) of 8.4 nm (24 h) and 7.2 nm (51 h). In contrast, Eu-NPs preferably exhibit an average ECD of 10.6 nm (10 h) and 12.3 nm (244 h). Au-NPs are classified predominantly as "very round" with an average reciprocal aspect ratio (RAR) of ~0.9 and a Feret major axis ratio (FMR) of ~1.17. Eu-NPs mainly belong to the "rounded" class with a smaller RAR of ~0.6 and a FMR of ~1.3. These results show that an increase in contact time is not accompanied by an average particle growth for Au-NPs, but by a doubling of the particle number. Anabaena sp. is capable of biosorbing and bioreducing dissolved Au3+ and Eu3+ ions from aqueous solutions, generating nano-sized Au and Eu particles, respectively. Therefore, it is a low-cost, non-toxic and effective candidate for a rapid recovery of these sought-after metals via the bioproduction of NPs with defined sizes and shapes, providing a high potential for scale-up.

Anisotropic Nanoparticle Arrays Guided by Ordered Nanowire Films Enhance Surface‐Enhanced Raman Scattering

AbstractDesigning high‐efficiency surface‐enhanced Raman scattering (SERS) substrates has attracted explosive attention in recent decades for their novel and potential applications. Great achievements have been made to optimize the intrinsic activity of nanomaterial in SERS substrates, while little attention has been paid to the unique structural design of the nanomaterial building blocks. Herein, a new strategy is provided for assembling Au nanoparticles into well‐defined ordered structures by using a highly ordered arrangement nanowires template to explore the ordering effect on the SERS performance. The highly ordered Au nanoparticle arrays show a detection limit of 10−9 m that exceeds disordered Au particles by two orders of magnitude, as well as over treble enhancement factor at the same detection concentration. Importantly, this novel scientific discovery can be further confirmed in various probed molecules or nanoparticles with different diameters, which means SERS substrate design can be pushed forward further combined with traditional intrinsic activity design.

In Situ Spectroscopy and Microscopy Insights into the CO Oxidation Mechanism on Au/CeO2(111)

In this work, we prepared and investigated in ultra-high vacuum (UHV) two stoichiometric CeO2(111) surfaces containing low and high amounts of step edges decorated with 0.05 ML of gold using synchrotron-radiation photoelectron spectroscopy (SRPES) and scanning tunneling microscopy (STM). The UHV study helped to solve the still unresolved puzzle on how the one-monolayer-high ceria step edges affect the metal-substrate interaction between Au and the CeO2(111) surface. It was found that the concentration of ionic Au+ species on the ceria surface increases with increasing number of ceria step edges and is not correlated with the concentration of Ce3+ ions that are supposed to form on the surface after its interaction with gold nanoparticles. We associated this with an additional channel of Au+ formation on the surface of CeO2(111) related to the interaction of Au atoms with various peroxo oxygen species formed at the ceria step edges during the film growth. The study of CO oxidation on the highly stepped Au/CeO2(111) model sample was performed by combining near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), UHV-STM, and near-ambient-pressure STM (NAP-STM). This powerful combination provided comprehensive information on the processes occurring on the Au/CeO2(111) surface during the interaction with CO, O2, and CO + O2 (1:1) mixture at conditions close to the real working conditions of CO oxidation. It was found that the system demonstrates high stability in CO. However, the surface undergoes substantial chemical and morphological changes as the O2 is added to the reaction cell. Already at 300 K, gold nanoparticles begin to grow using a mechanism that involves the disintegration of small gold nanoparticles in favor of the large ones. With increasing temperature, the model catalyst quickly transforms into a system of primarily large Au particles that contains no ionic gold species.

Gold Atomic Layers and Isolated Atoms on MoC for the Low-Temperature Water Gas Shift Reaction

Au 2–4 atomic layers, monolayers, and isolated atoms were generated by redispersing a Au particle (8 nm) during MoO3 carburization to α-MoC with a CH4/H2 mixture at 600–750 °C. The spherical Au particle initially wetted on the developing molybdenum carbides, reshaped into large thin films, then decomposed to smaller islands, and finally cracked into 2–4 atomic layers at 600 °C. These layered Au species further split into isolated atoms when carburized at 750 °C, which could be reversed into monolayers and 1–2 atomic layers by H2-treatment at 630–650 °C, followed by activation with a CH4/H2 mixture at 590 °C. When tested for the low-temperature water gas shift reaction, the 2–4 atomic layers possessed a much higher activity than the monolayers and isolated atoms. Interestingly, the specific reaction rate showed a volcano-type pattern with respect to the coordination number of Au–Au in the size-specified gold species, where the Au 2–4 atomic layers having a Au–Au coordination number of 7.7 were intrinsically more active. Detailed structural analysis, by STEM and EXAFS, identified that the interfacial gold atom coordinated simultaneously with the Mo atom in MoC and Au atoms in the layers.

Grain-Boundary-Induced Ultrasensitive Molecular Detection of Graphene Film.

Graphene has been considered a promising platform for molecular detection due to the graphene-enhanced Raman scattering (GERS) effect. However, the GERS performance of pristine graphene is limited by a low chemically active surface and insufficient density of states (DOS). Although diverse defects have been introduced, it remains a great challenge to improve the enhancement performance. Here, we show that graphene grain boundaries (GBs) possess stronger adsorption capacity and more abundant DOS. Thus, GERS performance increases with the atomic percentage of GBs, which makes nanocrystalline graphene (NG) film a superior GERS substrate. For R6G as a probe molecule, a low detection limit of 3 × 10-10 M was achieved. Utilizing the high chemical activity of GBs, we also fabricated NG film decorated with Au particles using a one-step quenching strategy, and this hybrid film exhibits an extremely low limit of detection down to 5 × 10-11 M, outperforming all the reported graphene-based systems.

Mild and Rapid Light-Driven Suzuki-Miyaura Reactions Catalyzed by AuPd Nanoparticles in Water at Room Temperature.

Organic reactions carried out in water under mild conditions are state-of-the-art in terms of environmentally benign chemical processes. In this direction, plasmonic catalysis can aid in accomplishing such tasks. In the present work, cyclodextrin-mediated AuPd bimetallic nanoparticles (NPs) were applied in room-temperature aqueous Suzuki-Miyaura reactions aiming at preparing biaryl products based on fluorene, isatin, benzimidazole and resorcinol, with yields of 77 % up to 95 %. AuPd NPs were revealed to be a physical mixture of Au and Pd particles circa 20 and 2 nm, respectively, through X-ray diffraction, dynamic light scattering, UV-Vis spectroscopy and transmission electron microscopy analyses.

Sunlight-Powered Reverse Water Gas Shift Reaction Catalysed by Plasmonic Au/TiO2 Nanocatalysts: Effects of Au Particle Size on the Activity and Selectivity.

This study reports the low temperature and low pressure conversion (up to 160 °C, p = 3.5 bar) of CO2 and H2 to CO using plasmonic Au/TiO2 nanocatalysts and mildly concentrated artificial sunlight as the sole energy source (up to 13.9 kW·m-2 = 13.9 suns). To distinguish between photothermal and non-thermal contributors, we investigated the impact of the Au nanoparticle size and light intensity on the activity and selectivity of the catalyst. A comparative study between P25 TiO2-supported Au nanocatalysts of a size of 6 nm and 16 nm displayed a 15 times higher activity for the smaller particles, which can only partially be attributed to the higher Au surface area. Other factors that may play a role are e.g., the electronic contact between Au and TiO2 and the ratio between plasmonic absorption and scattering. Both catalysts displayed ≥84% selectivity for CO (side product is CH4). Furthermore, we demonstrated that the catalytic activity of Au/TiO2 increases exponentially with increasing light intensity, which indicated the presence of a photothermal contributor. In dark, however, both Au/TiO2 catalysts solely produced CH4 at the same catalyst bed temperature (160 °C). We propose that the difference in selectivity is caused by the promotion of CO desorption through charge transfer of plasmon generated charges (as a non-thermal contributor).

Using ammonia solution to fabricate highly active Au/ uncalcined TS‑1 catalyst for gas-phase epoxidation of propylene

Reducing the Au particle size and increasing the number of defective Ti4+ species have been considered effective strategies to boost the catalytic performance of Au–Ti bifunctional catalysts used for propylene epoxidation utilizing H2 and O2. Consequently, the development of an effective method that can simultaneously achieve these goals is of significant scientific and industrial importance. Herein, we demonstrate, for the first time, that the simultaneous immobilization of small Au particles (approximately 1.6 nm) onto uncalcined titanium silicate-1 (i.e., TS-1-B) and facilitation of the formation of defective Ti4+ species can be achieved using a modified deposition–precipitation (DP) method utilizing ammonia solution as the precipitant. The as-synthesized catalyst exhibits a significantly enhanced propylene oxide (PO) formation rate combined with fascinating PO selectivity and hydrogen efficiency, which were better than the reference catalyst prepared via the DP urea (DPU) method and other reported Au/uncalcined TS-1 catalysts. The catalyst structure–performance relationship was established using multiple characterization studies. the ammonia treatment facilitates the hydrolysis of some of the ≡Ti-O-Si≡ bonds into defective Ti4+ species (i.e., Ti(OSi)3OH), which not only provides more active Ti4+ sites but also favors the uniform deposition of Au. This methodology and the insights stated herein may also be applicable for enhancing the dispersion of Au in a variety of zeolite-supported catalysts.

Sintering-resistant and highly active Au/SBA-15 catalyst for carbon monoxide oxidation

The low thermal stability of gold-based catalysts is a significant obstacle to their practical application, especially under demanding conditions, such as those prevailing in automotive exhaust gas converters. In this work, we demonstrate that it is possible to strongly anchor 2–3 nm size gold nanoparticles inside the pores of SBA-15 mesoporous silica. The Au/SBA-15 catalyst showed high thermal stability, even at a temperature of 700–800 °C. The gold was evenly distributed inside the SBA-15 mesopores using the adsorption of the [Au(en)2]Cl3 complex (en = ethylenediamine) in an alkaline environment. Due to the very small size of gold nanoparticles, the obtained catalyst was highly active in low-temperature CO oxidation. The high resistance of Au particles to sintering can be explained by the confinement effect and the strong metal-support interaction, induced during the catalyst precursor decomposition under an oxygen-free atmosphere at 400 °C. The carbonaceous layer, formed from ethylenediamine ligands decomposition, plays an essential role in stabilizing gold nanoparticles inside the SBA-15 pores. We believe that our findings may contribute to solving the problem of carbon monoxide emission during engine start-up.

Multifield Coupling of Local Surface Plasmon Resonance‐Assisted Au–TiO2 Photocatalysis Considering Bimodal Resonance and Superposition Effect

This study concerns the improvement of the synergetic catalytic efficiency of Au–TiO2 nanorods considering the local surface plasmon resonance (LSPR) effect of different Au nanoparticles (NPs). The absorption spectrum and selective absorption efficiency for visible light, the local electric field, and the generated thermal effect are specifically analyzed based on the multifield decoupling of LSPR‐assisted Au–TiO2 catalysts. The simulation results show that the extinction spectra of both spherical and ellipsoidal Au particles are consistent with the experimental data. Interestingly, the latter is characterized by significant bimodal resonance modes. Comparatively, the simulation results show that the longitudinal mode, which is sensitive to the aspect ratio, is more favorable for the improvement of the photocatalytic activities. It is found that the resonance peaks are highly controllable, and are linear to the particle size and aspect ratio. Meanwhile, the electric field mode of TiO2 is significantly increased under the resonance wavelength. It is worth mentioning that the superposition effect makes a non‐negligible impact on the actual catalysts, leading to a relative shift of resonance wavelength. The consideration of the hot spots caused by the superposition effect influence the photocatalytic results significantly, providing values in diminishing the inadaptability of the theory in near‐touching regions of plasma particles.

Large-area fluorescence enhancement of R6G based on a uniform PVA-Au plasmonic substrate.

With the development of surface enhanced fluorescence (SEF) spectroscopy technology, uniform and low-cost SEF substrate is urgently needed. In this paper, the nanocomposite films of poly (vinyl alcohol) (PVA) embedded with in-situ Au particles, their localized surface plasmon resonance (LSPR) bands locate at different wavelengths from 525 nm to 569 nm, were used as substrates to enhance the fluorescence of rhodamine 6 G (R6G). The results shows that the uniform light emission in large area can be measured, and the maximum enhancement factor (EF) is about 13 folds. With increasing concentration of R6G films, the EF first increases and then slowly decreases. It is demonstrated that the EF greatly depends on the matching degree of the emission/excitation of R6G and the LSPR band of PVA-Au substrate. All the results further suggests that the PVA-Au substrate not only realize the fluorescence enhancement but also attenuates the fluorescence quenching at higher concentration. In addition, the local electric distribution of the substrate is simulated by using three-dimensional finite different time-domain (FDTD) to further demonstrate the mechanism of the SEF. This substrate has good development prospects in the fields of fluorescent probes and fluorescence imaging, which can be beneficial to the development of uniform and low-cost SEF substrate.

Elimination of Indoor Volatile Organic Compounds on Au/SBA-15 Catalysts: Insights into the Nature, Size, and Dispersion of the Active Sites and Reaction Mechanism

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.

Synergistic electronic and geometric effects of Au/CeO2 catalyst for oxidative esterification of methacrolein

AbstractMethyl methacrylate (MMA) is an important monomer for the production of acrylic plastics and polymer dispersions. In this study, we demonstrate a strategy to synergize the electronic and geometric effects of the Au/CeO2 catalyst, achieving three orders of magnitude improvement in reaction rate for the oxidative esterification of methacrolein to MMA. The electronic properties of Au in terms of the valence electron population of 5d states are decoupled from the redox ability and acid–base properties of catalyst support as the main cause for the significant increase in the specific activity of the active site. Moreover, the Au edge site is identified as the main active site for this reaction, whose number reaches the maximum for the 1.6 nm‐sized Au particles. Hence, the synergism between the electronic (lower valence electron population of 5d states) and geometric (more edge active sites) promotions of the Au‐10/CeO2 catalyst contributes to the highest catalytic activity.

Multi-Effect Enhanced Raman Scattering Based on Au/ZnO Nanorods Structures.

Surface-enhanced Raman scattering (SERS) was considered a potential spectroscopic technique for applications of molecular detection and has drawn great research interest during the past decade. So far, fabrications of cost-effective SERS substrates with high sensitivity and stability and the corresponding enhanced mechanisms are always among the list of research topics, although great progress has been made. In this work, Au particles were decorated on Si, ZnO film and ZnO nanorod arrays simultaneously by an economical method of ion sputtering, generating three kinds of SERS substrates for R6G detection. The morphology difference of Au particles on different samples and the consequent influence on Raman scattering were studied. The experiment results exhibited that substrates with Au particles decorated on ZnO nanorods had the highest Raman enhancement factor. Furthermore, multi-effect enhanced mechanisms summarized as localized surface plasmon resonance (LSPR) filed coupling, electron transferring induced by LSPR of Au particles and whispering gallery mode (WGM) effect of the ZnO cavity were presented. This work provides a convenient and efficient method of fabricating SERS substrates and indicates that such proper metal/semiconductor composite structures are promising candidates for SERS applications.

Anomalous Small-Angle X-Ray Scattering of Fuel-Cell Catalyst Samples

Anomalous small-angle X-ray scattering (ASAXS) is a technique capable of extracting element-specific structural information from multi-element materials, and is considered useful in the structure analysis of metal alloy catalyst particles for fuel cells. ASAXS utilizes the resonant term of the atomic scattering factor of the element of interest. The resonant term has a real part (f1) and an imaginary part (f2), and f1 mainly contributes to the anomalous scattering phenomenon. The amplitude of f1 varies with X-ray energy, and decreases sharply around the absorption edges of the element. The decrease is as large as -18 electrons in the case of platinum (Pt) LIII-edge. ASAXS experiments are possible only in synchrotron radiation facilities where X-ray energies are freely tunable.ASAXS experiments require X-ray recordings at 3 or more different X-ray energies to mathematically isolate the element-specific component. Although the energy dependence of f1 seems substantial at around the absorption edge, its contribution to the total scattering intensity from a multi-element system is subtle, and high-precision measurements are required to obtain correct structural information.In actual measurements, experimental errors can arise from many sources, even in present-day third-generation synchrotron radiation facilities. They include fluctuations of the X-ray beam intensities and positions, the calibration error of X-ray energies, and time-dependent changes of sample properties. Here we evaluate the effect of such errors by using model calculations. The model consists of a mixture of 3-nm Pt particles and 5-nm gold (Au) nanoparticles.The scattering profiles of this mixture were calculated for X-ray energies of 11.504, 11.555 and 11.560 keV (Curve A in Figure 1. The LIII edge is at 11.564 keV). The scattering amplitude of the Pt particles was calculated by using the f1 and f2 values from the Cromer-Liberman tables (Brennan & Cowan, Rev. Sci. Instr., 63, 1992), using equations described by Sanada et al. (J. Am. Chem. Soc., 135, 2013). The scattering from Au particles (Curve B) was assumed to be independent of energy. The extracted scattering profile for Pt was identical to that calculated for a sample with Pt particles alone (Curve D, compare with C). Next, the scattering intensities at a specific energy were deliberately changed by a few percent before extracting the Pt contribution. For intensities at 11.56 keV, even a reduction of as slight as 0.2% resulted in catastrophic consequences (Curve F). With a 5% increase of intensity, the generated Pt profile superficially looked normal, but in reality the scattering curve retained the features of the Pt-Au mixture, meaning that the Pt-specific component was not successfully extracted (Curve D).These results indicates that the accuracy requirements in ASAXS measurements are very stringent, and every effort should be made to eliminate factors that can cause errors and uncertainties.In the meeting, data recorded from actual catalyst samples will also be presented, including those from MIRAI (fuel-cell vehicle manufactured by Toyota).This work was performed under the NEDO FC-Platform project. Figure 1

Orientation Selection of Supported Au Nanoparticles on (111)- and (001)-Terminated SrTiO3 Substrates

Orientation-dependent performance has been demonstrated in different materials consisting of nanoparticles on substrates. The fabrication of desirably oriented nanoparticles requires knowledge of orientation selection rules. Based on the Wulff–Kaishew theory, our analysis shows that the energy-favorable orientation(s), is influenced by the surface energy of particles, in addition to the dominant factor, i.e., the energy difference between particle/substrate interfacial energy and surface energy of the substrate. To verify this, a model system of dewetted Au nanoparticles on SrTiO3 is studied. The {111}-terminated SrTiO3 supports only {111}-orientated Au particles, with the lowest interfacial energy. On the other hand, {100}-terminated SrTiO3 supports multiple Au particles, with {111}-, {100}-, {110}- orientations, as a possible result of close surface energy contributions. The above orientations can be additionally manipulated by changing the heat treatment temperature. Our results provide fundamental insights into fabricating supported nanoparticles for practical applications.

Au/Sn-Beta catalyst with metal-Lewis acid cooperative sites steers aerobic oxidation of 5-hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is a potential substitute of petroleum-based terephthalic acid to manufacture polymer. The selective aerobic oxidation of renewable 5-hydroxymethylfurfural (HMF) to FDCA is a promising and appealing route for establishing sustainable and environmentally friendly chemical process. Au catalysts have exhibited exceptional catalytic performances for this highly anticipated chemical transformation, where the used support intensively impacts the catalytic productivity from the standpoint of metal-support and guest organic-support interactions. Herein, Sn-Beta zeolite was straightforward and rapidly synthesized via structural reconstruction without the auxiliary of any solvents, which was adopted as support for Au catalyst to construct bifunctional catalysts. As for Au/Sn-Beta sample, Lewis acid sites were related to Sn4+ ions in the zeolite framework, while electronic properties and particle size of Au species were capable of being modulated by Au dosages. In addition, charge transfer from Au species to framework Sn4+ ions resulted in the formation of Auδ+ species. Au/Sn-Beta catalyst with metal-Lewis acid cooperative active sites showed unique catalytic productivity of FDCA product in the aerobic oxidation of HMF to FDCA, whose catalytic performance was correlated with Lewis acid amounts as well as geometric and electronic effect of Au particle. Reaction mechanism analysis revealed the pathway and concrete step that Lewis acid site functioned. The aim is to provide some guidance for constructing a task-specific multifunctional supported catalyst from the view of support-enhanced effect for the catalytic conversion of biomass resource with multi-functional-groups.

Ultra-sensitive ethanol sensor with low detection limit based on mesoporous Au-loaded γ-Fe2O3 nanospheres

• Au-loaded γ-Fe 2 O 3 mesoporous nanospheres were prepared by a simple two-step process. • The sensor based on Au-loaded γ-Fe 2 O 3 exhibits superior performances to ethanol. • The sensor based on Au-loaded γ-Fe 2 O 3 can detect ethanol as low as 0.2 ppm (S = 2.3). • The synergistic effect of γ-Fe 2 O 3 and Au particles enhanced the sensing performance. Au-loaded γ-Fe 2 O 3 nanocomposites were prepared by a simple hydrothermal method and one-step amino acid synthesis. Through various characterization methods, it was found that the γ-Fe 2 O 3 nanospheres attached with gold nanoparticles were of high purity and mesoporous. The test results show that compared with pure γ-Fe 2 O 3 , the sensor based on mesoporous Au-loaded γ-Fe 2 O 3 nanospheres has superior performance, and it exhibits a high response value (S = 56.7) to 100 ppm ethanol at 200℃, short response/recovery times (2 s/9s), and excellent selectivity and long-term stability. Furthermore, the sensor can detect ethanol as low as 0.2 ppm (S = 2.3). The material is expected to be used for high-performance ethanol detectors.

Cu–Au nanoparticles produced by the aggregation of gas‐phase metal atoms for CO oxidation

AbstractAlloy nanoparticles (nanoalloys) are widely applied in heterogeneous catalysts, advanced electrodes, biomaterials, and other areas. The properties of nanoalloys can be tuned to a significant extent by their structures and compositions, which are governed by the employed synthetic procedure. Often such synthesis occurs in non‐equilibrium conditions and yields nanoalloys with structures and properties that are different from those obtained in thermodynamic equilibrium. In this work, we characterize how the non‐equilibrium conditions during the synthesis of Cu–Au alloys via physical vapor deposition (PVD) affect their morphology, composition, electronic structure, and reactivity in CO oxidation. We used molecular dynamics to simulate the PVD synthesis of Cu–Au nanoalloys through the non‐isothermal aggregation of Cu and Au atoms at a 3:1 ratio in the Ar atmosphere to obtain realistic structures of Cu–Au nanoparticles. Due to the different aggregation kinetics of Au and Cu atoms, the average Au concentration in the obtained Cu–Au particles varied between 14% and 50% depending on the nanoparticle size and the aggregation time. Density functional simulations revealed that the reactivity of the obtained Cu–Au clusters toward CO and oxygen as well as Brønsted–Evans–Polanyi relations for CO oxidation significantly depend on whether the clusters had fcc, icosahedral, or amorphous structures and do not strongly correlate with the d‐band centers of the adsorption sites. Our study highlights the importance of the non‐equilibrium character of nanoalloy structure and composition for their electronic structure and catalytic properties. The performed analysis of the reactivity of Cu–Au clusters with realistic structures in CO oxidation will help the optimization of Cu–Au catalysts for this societally important reaction.

Insight into the transient inactivation effect on Au/TiO2 catalyst by in-situ DRIFT and UV–vis spectroscopy

Au catalysts have drawn broad attention for catalytic CO oxidation. However, a molecular-level understanding of the reaction mechanism on a fast time-resolved scale is still lacking. Herein, we apply in situ DRIFTS and UV-Vis spectroscopy to monitor the rapid dynamic changes during CO oxidation over Au/TiO2. A pronounced transient inactivation effect likely due to a structural change of Au/TiO2 induced by the reactants (CO and O2) is observed at the beginning of the reaction. The transient inactivation effect is affected by the ratio of CO and O2 concentrations. More importantly, during the unstable state, the electronic properties of the Au particles change, as indicated by the shift of the CO stretching vibration. UV-Vis spectroscopy corroborates the structure change of Au/TiO2 surface induced by the reactants, which leads to a weakening of the Au catalyst’s ability to be oxidized (less O2 adsorption), resulting in the transient inactivation effect.