Au Nanoparticle Catalysts Research Articles

The surface structural changes of self-assembly monolayer Au nanoparticles and their regulated catalytic activity

In this paper, Au nanoparticles (AuNPs) were in - situ synthesized on the shell layer of the core-shell type polystyrene/SiO2/poly(N-isopropylacrylamide- co -3-methacryloxypropyltrimethoxysilane) (PS/SiO2/P(NIPAM- co - MPTMS)) composite microspheres with inorganic-organic hybrid network structure as support. The supported AuNPs catalysts were obtained by using self-assembly of alkanethiol compound with the different chain length on the surface of AuNPs. We chose the reduction of 4-nitrophenol (4-NP) as a model reaction. The results were demonstrated that the surface structure of AuNPs can be regulated via changing the dosage of sodium borohydride reducing agent. In addition, the catalytic activity was significantly influenced by the chain length and modified amounts of the alkanethiol. The results have found that the desorption of Au-S bond is prefer to form the local reaction micro-sites comprising of alkyl chain. Therefore, the catalytic performance could be regulated by changing the surface structures of the alkanethiol self-assembly monolayer (SAMs) on the AuNPs surface.

Zn-doping of GaAs nanowires grown by Aerotaxy

Nanowires were grown by means of a novel aerosol-based method called Aerotaxy. Here an aerosol of Au catalyst nanoparticles in N2 is mixed with MOVPE precursors in a flow-through reactor at atmospheric pressure, whereby nanowires are produced continuously in high concentrations. We demonstrate the possibility of in situ doping of the NWs and the realization of well-controlled p-type GaAs nanowires using this Aerotaxy method. By controlling the cracking and concentration of the precursors, p-doped GaAs nanowires could be grown exhibiting a wide range of Zn doping levels. DEZn was used as the dopant source and the injected DEZn/TMGa ratio was varied from 0.1% to 3.4%. The morphology, the crystalline structure and the composition of the nanowires were studied using SEM, TEM and XEDS. The nanowires were grown straight without any significant tapering and this ideal morphology could be maintained up to an injected DEZn/TMGa ratio of 3.4%. The nanowires typically grew in the 〈111〉 direction with a pure zincblende structure, but by increasing the DEZn flow the number of twinning defects increased which we ascribe to Zn incorporation. Elemental analysis shows a high Zn content in the catalyst particle and also a gradient in the Zn content along the nanowire. The samples were analyzed optically using photoluminescence (PL). From the result we estimated the free hole concentration induced by Zn acceptors to be 1×1020cm−3 for DEZn/TMGa ratio of 3.4%. To our knowledge this is the first report on in situ doping of GaAs nanowires grown by Aerotaxy.

Facile synthesis of three-dimensionally ordered macroporous LaFeO3-supported gold nanoparticle catalysts with high catalytic activity and stability for soot combustion

A strategy for the facile synthesis of three-dimensionally ordered macroporous (3DOM) LaFeO3-supported gold nanoparticle catalysts is reported, namely in situ colloidal crystal template (CCT) method. The synthetic process involving in three steps are listed in detail, for example, the synthesis of monodisperse polymethyl methacrylate (PMMA) microspheres accompanied with polyelectrolyte brushes ([NH2]+·Cl−, PEBs), the preparation and assembling of CCT with spherical Au/PMMA compound, and the formation of 3DOM LaFeO3-supported gold catalysts via calcination to remove the CCT. All the catalysts have well-defined 3DOM structures, and gold nanoparticles are uniformly dispersed on the inner wall of 3DOM LaFeO3 support. 3DOM structure can improve the contact efficiency between soot particle and catalyst, and the strong metal (Au)-oxides (LaFeO3) interaction provides the active sites for activation of O2. 3DOM Aun/LaFeO3 catalysts obtained by in situ CCT method show high catalytic activity and stability for diesel soot oxidation. It suggests that 3DOM Aun/LaFeO3 catalysts are excellent systems for catalytic oxidation of solid soot particle, and the design concept and facile synthesis method of 3DOM oxide-supported Au nanoparticle catalysts can be extended to other metal/oxide compositions.

Comparison of Au and TiO2 based catalysts for the synthesis of chalcogenide nanowires

We present a comparative study of TiO2-based and Au catalysts for the physical vapor deposition of (Bi1−xSbx)2Se3 topological insulator nanowires. The standard Au nanoparticle catalyst was compared to five TiO2 nanoparticle based catalysts (anatase, rutile, P-25, high surface area anatase, and TiO2 supported Au particles). The use of Au nanoparticles seriously harms the properties of nanowires, thereby limiting their application. In contrast, TiO2 based catalysts lead to the residue-free growth of nanowires with a higher degree of crystallinity. Homogeneous nanowire ensembles are achieved with the mixed phase P-25 catalyst, and a possible growth mechanism is proposed.

Low-pressure ETEM Studies of Au assisted MgO Nanorod Growth

Environmental transmission electron microscopy (ETEM) studies MgO nanorod growth from Au catalyst nanoparticles in a controlled gas atmosphere have been performed, in order to elucidate the mobility of Au surface atoms and the configuration of the Au/MgO interface. MgO nanorod growth is driven by the electron beam and found to be strongly dependent on the gaseous environment in the microscope and electron beam current density.

ChemInform Abstract: Highly Efficient Etherification of Silanes by Using a Gold Nanoparticle Catalyst: Remarkable Effect of O2.

O2 is acting! A nanosized hydroxylapatite-supported Au nanoparticle (NP) catalyst exhibited high activity under aerobic conditions, and various silyl ethers could be obtained from diverse combinations of silanes with alcohols. Moreover, O2 was found to act not as a stoichiometric oxidizing reagent, but as a non-consumed promoter, significantly boosting the catalytic activity of AuNPs.

Reductive Deprotection of Monolayer Protected Nanoclusters: An Efficient Route to Supported Ultrasmall Au Nanocatalysts for Selective Oxidation

The synthesis and investigation of the catalytic properties of Au nanoparticles (AuNPs) is an area of intense research. Despite much effort being made to this field, attaining both high catalytic activity and selectivity at the same time remains elusive. Herein a new mild reductive thiolate-deprotection strategy is reported to prepare nanoporous silica-supported ultrasmall AuNP catalysts that show very efficient catalytic activity and high selectivity for oxidation reactions.

Surfactant-assisted preparation of surface-enhanced Raman scattering-active substrates

As shown in the literature, cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been predominantly employed in the shape-controlled synthesis of Au nanoparticles (NPs) in solution to produce the corresponding shape-dependent Au NP catalysts. Among the different techniques used to obtain rough metal substrates with surface-enhanced Raman scattering (SERS) activities, controllable and reproducible surface roughness can be generated using an electrochemical process. In this work, innovative SERS-active substrates with Au NPs are prepared for the first time using sonoelectrochemical deposition-dissolution cycles (SEDDCs) in CTAB-containing electrolytes. Encouragingly, the SERS intensity for both the model probe molecule Rhodamine 6G (R6G) and the general example molecule 4-mercaptopyridine (4-MPy) adsorbed onto the developed substrates are higher by more than one order of magnitude compared with R6G and 4-MPy adsorbed onto SERS-active substrates prepared in solutions in the absence of CTAB. Moreover, the limits of detection (LOD) recorded for the developed SERS-active substrates are as low as 2 × 10−15 and 1 × 10−10 M for R6G and 4-MPy, respectively.

Hollow γ-Al2O3 microspheres as highly “active” supports for Au nanoparticle catalysts in CO oxidation

Consisted of closely packed nanoflakes, γ-Al2O3 hollow microspheres with ca. 4–6 μm in diameter, and 500–700 nm in shell thickness have been hydrothermally synthesized through utilizing Al(NO3)3·9H2O as precursor, urea as precipitant agent and sulfate K2SO4, (NH4)2SO4, or KAl(SO4)2·12H2O as additive, followed by a calcination step. The samples were further characterized by thermogravimetric analysis, scanning electron microscope, x-ray powder diffraction, nitrogen adsorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO etc. The morphology of alumina products was strongly dependent on the presence of SO4 2−. Then via a deposition–precipitation method, 3 wt.% Au nanoparticles supported on γ-Al2O3 hollow microspheres exhibit excellent performance with a complete CO conversion at 0 °C (T 100% = 0 °C) and 50 % conversion at −25 °C (T 50% = −25 °C). The good catalytic activity is associated with the special hollow microsphere structures assembled by nanoflakes of γ-Al2O3 support. The DRIFTS confirms the presence of Auδ+ and Au0 on the surface of γ-Al2O3 hollow microspheres. As a contrast, Au catalyst prepared using alumina support with undefined morphology shows low activity under the same catalytic test conditions (T 100% = 190 °C, T 50% = 80 °C).

Selective electro-oxidation of glycerol to tartronate or mesoxalate on Au nanoparticle catalyst via electrode potential tuning in anion-exchange membrane electro-catalytic flow reactor

A potential-controlled glycerol oxidation to tartronate or mesoxalate was demonstrated on Au nanoparticle catalysts in a self-designed anion-exchange membrane electro-catalytic flow reactor. The investigation clearly shows that by tuning the anode potential from 0.35 to 0.65V, the selectivity to tartronate dropped from 79% to 26%, while that to mesoxalate increased from 0% to 57%. The tests also indicate that the elongation of reaction time will only increase the glycerol conversion, having little effects on the product distribution. The work may open a new route for the controllable oxidation of biorenewable polyols to valuable chemicals.

Highly Efficient Etherification of Silanes by Using a Gold Nanoparticle Catalyst: Remarkable Effect of O2

O2 is acting! A nanosized hydroxylapatite-supported Au nanoparticle (NP) catalyst exhibited high activity under aerobic conditions, and various silyl ethers could be obtained from diverse combinations of silanes with alcohols. Moreover, O2 was found to act not as a stoichiometric oxidizing reagent, but as a non-consumed promoter, significantly boosting the catalytic activity of AuNPs.

Direct Amidation from Alcohols and Amines through a Tandem Oxidation Process Catalyzed by Heterogeneous‐Polymer‐Incarcerated Gold Nanoparticles under Aerobic Conditions

We describe herein a highly elegant and suitable synthesis of amide products from alcohols and amines through a tandem oxidation process that uses molecular oxygen as a terminal oxidant. Carbon-black-stabilized polymer-incarcerated gold (PICB-Au) or gold/cobalt (PICB-Au/Co) nanoparticles were employed as an efficient heterogeneous catalyst depending on alcohol reactivity and generated only water as the major co-product of the reaction. A wide scope of substrate applicability was shown with 42 examples. The catalysts could be recovered and reused without loss of activity by using a simple operation.

Selective oxidation of ethanol to acetaldehyde by Au−Ir catalysts

The use of Ir as a reactive transition metal for O2 activation to facilitate the selective oxidation of ethanol to acetaldehyde is explored. Co-impregnation of the chlorides of Au and Ir on SiO2 followed by reduction afforded small bimetallic nanoparticles with a varying Au/Ir ratio. All of the nanoparticle catalysts including the monometallic Au and Ir end members have sizes in the range of 2–3nm. Infrared spectroscopy of adsorbed CO on the reduced catalysts evidences the formation of alloyed nanoparticles. After oxidation at room temperature and at 200°C, the Ir surface atoms are oxidized. No synergy between Au and Ir is observed in CO oxidation. Au lowers the CO oxidation activity of the pure Ir catalyst, suggesting the presence of surface Au atoms in the mildly oxidized Au–Ir bimetallic catalysts. At higher oxidation temperatures, viz. 350 and 500°C, bulk oxidation of Ir occurs. While pure Ir nanoparticles sinter upon oxidation at elevated temperatures (350–500°C), the presence of Au significantly retards this agglomeration of the nanoparticles. At these elevated temperatures, an intimate mixture of reduced Au and IrOx is formed. The Au–Ir nanoparticles display enhanced activity in ethanol oxidation to acetaldehyde, outperforming their monometallic counterparts, with only minimum loss of C2-oxygenates selectivity compared to the pure Au nanoparticle catalyst. The maximum activity is obtained for a Au–Ir3 composition. The present results can be explained by a model involving an intimate contact between Au sites for (dissociative) ethanol adsorption and Ir sites covered by O adatoms which catalyze C–H bond cleavage to yield acetaldehyde.

Au 나노입자가 코팅된 그래핀 기반 CO2가스센서의 제작과 그 특성

This paper describes the fabrication and characterization of graphene based carbon dioxide (<TEX>$CO_2$</TEX>) gas sensors. Graphene was synthesized by thermal decomposition of SiC. The resistivity <TEX>$CO_2$</TEX> gas sensors were fabricated by pure graphene and graphene decorated Au nanoparticles (NPs). The Au NPs with size of 10 nm were decorated on graphene. Au electrode deposited on the graphene showed Ohmic contact and the sensors resistance changed following to various <TEX>$CO_2$</TEX> concentrations. Resulting in resistance sensor using pure graphene can detect minimum of 100 ppm <TEX>$CO_2$</TEX> concentration at <TEX>$50^{\circ}C$</TEX>, whereas Au/graphene can detect minimum 2 ppm <TEX>$CO_2$</TEX> concentration at same at <TEX>$50^{\circ}C$</TEX>. Moreover, Au NPs catalyst improved the sensitivity of the graphene based <TEX>$CO_2$</TEX> sensors. The responses of pure graphene and Au/graphene are 0.04% and 0.24%, respectively, at <TEX>$50^{\circ}C$</TEX> with 500 ppm <TEX>$CO_2$</TEX> concentration. The optimum working temperature of <TEX>$CO_2$</TEX> sensors is at <TEX>$75^{\circ}C$</TEX>.

Aerobic oxidation of benzyl alcohol over mesoporous Mn-doped ceria supported Au nanoparticle catalyst

In this decade intensive research was carried out to prepare mesoporous non-silicious oxide for various application. Development of mesoporous ceria based material has become most important because of its application in catalysis, solar cell and photovoltic cell. The selective aerobic oxidation of primary alcohols through an environment benign route to synthesize aldehydes is of utmost importance. The catalytic role of supported gold nanoparticles for aerobic oxidation reaction has been focused in the era of sustainable chemistry. The unique redox property of ceria is a fascination for developing Au–CeO2 catalyst in many studies on aerobic oxidation reaction. In this work, we have prepared mesoporous manganese doped ceria to examine the change of physicochemical properties due to incorporation of managnese to the ceria lattice. Deposition of gold nanoparticles and Mn-doping on ceria enhanced the redox behaviour of ceria as well as the basic properties. A thorough characterization by BET S.A., XRD, Raman, HRTEM, STEM, H2-TPR, CO2-TPD, XPS, XAFS reveal the distortion of in the doped CeO2 lattice is electronic in nature rather than structural distortion. The catalytic activity of the catalysts demonstrate the promotional role of gold nanoparticle in this study.

Colorless alkaline solution of chloride-free gold acetate for impregnation: An innovative method for preparing highly active Au nanoparticles catalyst

An easy and versatile method for the preparation of gold nanoparticles catalyst from aqueous alkaline solution of chloride-free gold acetate has been developed. Au nanoparticles can be deposited on various supports only by impregnating them with the stocked solution of it and by the following calcination. Although the solubility of gold acetate is considerably low in water, we have successfully dissolved it completely by refluxing the brown colloidal dispersion of gold acetate with a pH adjusted to 10–11 at the boiling temperature. The resultant solution was transparent without any color, which should contain anionic Au(III) species like Au(OH)4−. Metal oxide powder such as Al2O3, CeO2, TiO2, SiO2 as well as silicates such as saponite clay, and Y-type zeolites was impregnated with the solution and then calcined at 623K. After washing and drying, the deposition of Au nanoparticles (<6nm) was confirmed by TEM, XRD and EXAFS on any supports regardless of their widely different isoelectric point. For gas phase CO oxidation, the Au/CeO2 prepared by this method was more active than those prepared according to conventional deposition–precipitation or impregnation methods by using HAuCl4 as a source of gold. The smallest mean particle size of Au (2.3±0.8nm) was obtained on saponite clay, which was highly active for glucose oxidation performed in aqueous phase at 333K.

UV-enhanced room-temperature gas sensing of ZnGa2O4 nanowires functionalized with Au catalyst nanoparticles

ZnGa2O4 nanowires were synthesized using a thermal evaporation technique. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction revealed that the nanowires were single crystals 30–200 nm in diameter and ranged up to ∼100 μm in length. The sensing properties of multiple networked ZnGa2O4 nanowire sensors functionalized with Au catalyst nanoparticles with diameters of a few nanometers toward NO2 gas at room temperature under UV irradiation were examined. The sensors showed a remarkably enhanced response and far reduced response and recovery times toward NO2 gas at room temperature under 254 nm-ultraviolet (UV) illumination. The response of ZnGa2O4 nanowires to NO2 gas at room temperature increased from ∼100 to ∼861 % with increasing the UV intensity from 0 to 1.2 mW/cm2. The significant improvement in the response of ZnGa2O4 nanowires to NO2 gas by UV irradiation is attributed to the increased change in resistance due to the increase in the number of electrons participating in the reactions with NO2 molecules by photo-generation of electron–hole pairs.

Electrical, photoelectrical and morphological properties of ZnO nanofiber networks grown on SiO2 and on Si nanowires

ZnO nanofibre networks (NFNs) were grown by vapour transport method on Si-based substrates. One type of substrate was SiO2 thermally grown on Si and another consisted of a Si wafer onto which Si nanowires (NWs) had been grown having Au nanoparticles catalysts. The ZnO-NFN morphology was observed by scanning electron microscopy on samples grown at 600 °C and 720 °C substrate temperature, while an focused ion beam was used to study the ZnO NFN/Si NWs/Si and ZnO NFN/SiO2 interfaces. Photoluminescence, electrical conductance and photoconductance of ZnO-NFN was studied for the sample grown on SiO2. The photoluminescence spectra show strong peaks due to exciton recombination and lattice defects. The ZnO-NFN presents quasi-persistent photoconductivity effects and ohmic I-V characteristics which become nonlinear and hysteretic as the applied voltage is increased. The electrical conductance as a function of temperature can be described by a modified three dimensional variable hopping model with nanometer-ranged typical hopping distances.

Thermally responsive gold nanocatalysts based on a modified poly-vinylpyrrolidone

Poly-vinylpyrrolidone (PVP) stabilized nanoparticle (NP) catalysts are among the most active NP catalysts demonstrating excellent activities and stabilities in a wide and diverse range of reactions. One of the main limitations, that tend to prevent their use in industrial processes, is that they cannot be easily separated from reactions that are not amenable to biphasic separations, i.e. those involving hydrophilic reaction products. We describe a durable and recyclable Au NP catalyst system based on modified PVP that is thermo-sensitive, termed C1-PVP. C1-PVP stabilized Au NPs are similar in size, and exhibit similar properties, to Au NPs stabilized by PVP, but their additional thermo-sensitivity enables their facile separation from hydrophilic reaction products by mild heating, resulting in their precipitation. XRD, XPS, TEM, temperature dependant NMR, DLS and UV–vis analysis, as well as catalytic recycling and metal leaching tests were carried out to fully characterize the thermo-sensitive behavior of C1-PVP stabilized Au NPs. The C1-PVP stabilized Au NPs were systematically compared to Au NPs stabilized by PVP demonstrating the superiority of the new system and their potential green benefits.

Supported Pt, Pd and Au nanoparticle anode catalysts for anion-exchange membrane fuel cells with glycerol and crude glycerol fuels

Carbon supported Pt, Pd, and Au nanoparticles (NPs) catalysts with small diameters (2.4–3.5nm) were prepared through a solution-phase reduction method, and applied as the model catalysts for electro-oxidation of both high-purity glycerol and biodiesel-derived crude glycerol. The half cell investigations showed that Pt/C has the highest activity in the low potential range, which can be further facilitated at elevated temperatures. The anion-exchange membrane fuel cells (AEMFCs) investigations demonstrated no obvious drop in peak power density on Pt/C anode, when the fuel was switched from high-purity glycerol to crude glycerol, indicating a good stability of the Pt/C against poisoning/deactivation from the impurities in crude glycerol. The tests also showed that on all these three model catalysts, a volcano-type relationship exists between the fuel cell performance and crude glycerol concentration at a fixed KOH concentration, while with a given crude glycerol concentration, the performance monotonically increased with the KOH concentration increasing. The highest performances were achieved with 6.0M KOH+1.0M crude glycerol at 80°C, which are 184.2, 93.9, and 50.1mWcm−2 on Pt/C, Pd/C, and Au/C anodes, respectively.