Au catalysts with different metallic particle sizes and supported on silica, alumina, titania, zirconia, ceria, and niobia were prepared, and the reduced catalysts were characterized by EXAFS ...spectroscopy. As the Au
Au coordination number decreased, the interatomic bond length decreased. The Au
Au bond length contraction appears to be independent of the support type. A correlation between the dispersion of Pt catalysts determined by hydrogen chemisorption and the EXAFS Pt
Pt coordination number was established and used to determine the dispersion of fully reduced Au catalysts. In addition, the Au particle size was estimated using a literature correlation of the EXAFS coordination number. For particles larger than about 40 Å, there was little change in the metallic bond length, whereas in catalysts with gold particles smaller than 30 Å, the Au
Au distance decreased with decreasing particle size, with a maximum contraction of about 0.15 Å. Decreasing particle size also brought a decrease in the intensity of the white line of the XANES spectrum. Both the decrease in bond distance and white line intensity were consistent with an increase in the d-electron density of Au atoms in very small particles. Au particles smaller than about 30 Å were also reactive to air, leading to oxidation of up to 15% of the atoms of the gold particles, depending on the size; larger particles were not oxidized. These oxidized Au atoms in small particles are suggested to be active for CO oxidation.
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•Gold-supported catalysts were prepared using TS-1 with a small amount of vanadium.•The added vanadium was incorporated into the molecular sieve framework of TS-1.•Propylene ...conversion was maintained in Au/V-TS-1 even at low H2 concentrations.•Au/V-TS-1 maintained selectivity for propylene oxide at lower H2 concentrations.
The direct epoxidation of propylene to propylene oxide (PO) represents a unique feature of gold nanoparticle catalysts. Different amounts of vanadium were introduced into TS-1 using a hydrothermal method to give V-TS-1, and the effect of various vanadium loadings on the catalytic performance of Au/V-TS-1 was investigated in the epoxidation of propylene under different reaction conditions. The obtained characterization results indicate that the molecular sieve pore structure and crystalline phase structure of TS-1 were maintained after vanadium incorporation, and vanadium was incorporated into the molecular sieve framework. The introduction of an appropriate amount of vanadium resulted in the homogeneous dispersion of gold particles with a small average particle size, which facilitated the epoxidation reaction. When V was introduced into TS-1, the propylene conversion decreased under the condition of 10 % H2 concentration (C3H6/H2 = 1/1) in the reaction atmosphere, but the PO selectivity was maintained. Interestingly, when the H2 concentration in the reaction atmosphere was lowered to 2 % (C3H6/H2 = 3/1), the propylene conversion in Au/TS-1 was significantly decreased compared to 10 % H2 concentration condition, while in Au/V-TS-1, the propylene conversion was maintained in 2 % H2 concentration condition compared to 10 % H2. Au/V-TS-1 also maintained its selectivity for PO even when the H2 concentration was lowered. Therefore, under low hydrogen concentration conditions, the PO formation rate of Au/V-TS-1 was much higher than that of Au/TS-1. More, the same trend was observed when Mo was added in place of V. Our strategy will guide the design of future catalysts as a way to utilize hydrogen more effectively while maintaining PO productivity.
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•ZIF-8 decorated Au/Al2O3 hybrid material Au@ZA was successfully prepared.•Au@ZA provided higher selectivity and prevented the loss or aggregation of Au particle.•The conversion and ...selectivity did not decrease significantly after 8 times cycles over Au@ZA.•Au@ZA exhibited significant differences in electronic interactions between CAL and COL.
Recycling of supported Au catalysts is challenging because of aggregation or loss of Au. Here, we report a strategy for introducing ZIF-8 into traditional Au/Al2O3 surface. The introduction of ZIF-8 can not only provide higher selectivity for the reaction products, but also prevent the loss or aggregation of the Au catalyst. From a series of characterizations, it can be seen that the ZIF-8 decorated Au/Al2O3 hybrid material Au@ZA (Z refers to ZIF-8, A refers to Al2O3) was successfully prepared. Au nanoparticles have better dispersion on the composite carrier, and the particle size is smaller. In the hydrogenation reaction of cinnamaldehyde (CAL), the Au@ZA composite catalyst has both the high chemical stability and the high selectivity of cinnamyl alcohol (COL) due to the micropore size effect of ZIF-8. The Au@ZA catalyst has ∼ 85 % COL selectivity when the CAL conversion is close to 100 %. And after 8 times of repeated use, the conversion of CAL and the selectivity of COL did not decrease significantly. It should be noted that just when a small amount of ZIF-8 is present, the synergistic catalytic effect mentioned above can be produced.
To minimize the poisoning of Pt-catalyst in glucose electro-oxidation for direct glucose fuel cell, carbon supported low metal loaded platinum–gold (Pt–Au/C) catalyst (1:1) was synthesized by ...immobilizing metal sols on carbon. The physical characterization of Pt–Au/C, Pt/C and Au/C was carried out using transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). SEM indicates the uniformity in loading of metals on Vulcan XC-72 carbon support, whereas TEM picture and XRD pattern confirm the formation of Pt–Au nanoparticles of less than 10 nm size. TGA shows the metal present in Pt–Au/C catalyst is 14.5% by wt. Electrochemical analysis such as cyclic voltammetry (CV) and chronoamperometry (CA) on Pt–Au/C and commercial Pt/C and Au/C (40 wt. % of metal) for glucose electro-oxidation in alkaline media shows that Pt–Au/C is capable of electro-oxidation of glucose at low potential as that of Pt/C catalyst and more active than Au/C catalyst. The poisoning rate of prepared Pt–Au/C (0.0046% s−1) is lower than that of Pt–Ru/C (0.0085% s−1) and Pt/C (0.011% s−1) catalysts. A batch cell operated using Pt–Au/C as anode and activated charcoal as cathode delivered 0.9 V OCV and 0.72 mW cm−2 peak power density at 0.2 M glucose in 1 M KOH solution.
We report the high performance of Au-coated SnO2 nanorod gas sensors for the detection of hazardous indoor volatile organic compounds (VOCs), such as benzene, toluene, xylene, and formaldehyde (BTXF) ...gases. Densely ordered SnO2 nanorod arrays were prepared via glancing angle deposition with an electron beam evaporator. The Au layer coating was used as a heterogeneous catalyst to promote the oxidation of VOCs, such as hydrocarbons. After optimizing the Au thickness, the sensor exhibited an excellent sensing response and a rapid response time of < 2.5 s for 10 ppm of BTXF gases. The maximum response was ∼662 for formaldehyde at 400 °C, ∼328 for toluene at 450 °C, ∼170 for xylene at 400 °C, and ∼139 for benzene at 500 °C, which are significantly higher than those of previously reported metal-oxide-semiconductor-based sensors. Each gas was selectively detected by integrating the sensor into a miniaturized gas chromatography (GC) system. The sensors detected ppb-level gas concentrations. Significantly, GC analysis revealed that four types of gases could be separately detected in a mixed gas within 5 min. Our study shows that Au-coated SnO2 nanorod gas sensors integrated with GC can be used as a facile indoor pollutant monitoring system.
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•We present the high-performance Au-coated SnO2 nanorod sensor for real-time indoor air pollutant monitoring.•The sensor exhibited an excellent sensing performance for benzene, toluene, xylene, and formaldehyde.•Each gas was able to detect at ppb-level by integrating the sensor into a miniaturized gas-chromatography (GC) system.•Significantly, four types of gases could be separately detected in a mixed gas within 5 min.
Au nanoparticles with diameters about 1.4 nm were dispersed onto porous Si3N4 grids and applied for growing single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition. Particularly, SWCNTs ...with diameters in the range of 0.75–1.8 nm were produced at a reaction temperature of 700 °C using CO as the carbon precursor. Nanobeam electron diffraction characterizations revealed that most of the SWCNTs have large chiral angles and zigzag SWCNTs were hardly detected. Density functional theory calculations showed that the SWCNT-Au interface formation energy and the SWCNT growth kinetics account for the enrichment of large chiral angle SWCNTs in the product.
To correlate single-walled carbon nanotube chirality with the element of Au, thermal chemical vapor deposition growth is performed on uniform Au nanoparticles at 700 °C using CO as the carbon precursor. The nanotube chirality distribution is determined by electron diffraction technique, which reveals a bias to large chrial angle species, a result of low tube-Au interface formation energy and high stability of the extruded edge hexagons. Display omitted
This comprehensive review article highlights recent advancements of Pt and Pd-based electrocatalysts, covering Pt and Pd alloys, Pt-M and Pd-M core-shell structures, nanosize/nanostructure effects, ...addition of support material, doping effects, and post-treatment for the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in Proton exchange membrane fuel cell (PEMFC). Additionally, it delves into other precious metals such as Gold (Au) and Silver (Ag) for ORR and HOR in PEMFC. The role and contribution of incorporating other elements or materials such as metal oxides, metal carbides, transition metal oxides, carbon support, and non-carbon support are thoroughly discussed. The most promising methods are also described, with a special emphasis on narrow particle size, nanostructure, and low loading of novel Pt- and Pd-based catalysts. Furthermore, the advantages and shortcomings of these catalysts for electrocatalysis are analyzed, along with the influence of the nanostructure and morphology of the electrocatalyst materials on electrochemical performance.
•Pt, Pd, Au, and Ag-based catalysts show promise for oxygen reduction and hydrogen oxidation reactions.•Binary and ternary Pt-M and Pd-M (M = Fe, Co, Ni, etc) alloy catalysts improved catalytic activities.•Numerous innovative synthesis techniques can generate highly improved nanostructure electrocatalysts.•Improving nano-size effects with metal carbides, transition metal oxides, and supports enhance electrochemical activities.
•Post-synthetic modification of Co(BDCNH2)with palladacycle complex.•Study of the investigation of its properties in allylamino E-enamides.•Post-synthetic modification (PSM) of MOFs.
An efficient and ...reusable catalyst by stepwise post-synthetic modification (PSM) of surface nitrogen-enriched Co(BDCNH2) metal-organic frameworks (MOFs) to synthesize the Co(BDCNH2)-AuNTf2 complex. The Co(BDCNH2)-AuNTf2 catalyst shows excellent performance when bonding AuNTf2 NPs to the Co(BDCNH2) substrate. The structure of the catalyst Co(BDCNH2)-AuNTf2 was elucidated by FT-IR, XRD, SEM, BET, EDS, ICP, and TGA techniques. Furthermore, the catalytic activity of the heterogeneous Au catalyst was investigated in the intermolecular hydroamination reactions of allenamides with arylamines, and the synthesis of allylamino E-enamides was carried out in very high yield and selectivity under mild conditions at low catalyst ratios. One of the most important advantages of the catalyst is that it can be recovered by centrifugation without significant loss of catalytic activity and can be easily reused repeatedly.
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