Au-Pt heteroaggregate nanostructures were prepared by sequential reduction methods. The structures have approximately 11 nm Au cores with Pt "tendrils" attached to the Au surface. The heteroaggregates are active H2 oxidation catalysts and show high activity at 90 degrees C in the presence of 1000 ppm CO. The surprising CO-tolerant behavior arises from the composition and unusual architecture of the particles.

Cores to celebrate: At 370 °C, Pt@Cu core–shell nanoparticles rapidly alloy but the reciprocal core–shell nanoparticles, Cu@Pt (see STEM images, left: Cu spectral map; middle: Pt spectral map; right: bright‐field image), are kinetically stabilized and show high activity and selectivity for NO reduction.

A facile ultrasonication‐assisted wet chemistry method for preparing multicomponent alloy nanoparticles (NPs) including high‐entropy alloys (HEAs) is reported. PtAuPdRhRu alloy (HEA), quaternary PtAuPdRh alloy, and ternary PtAuPd alloy NPs are produced with ≈3 nm in diameter. Taking advantage of the acoustic cavitation phenomenon in ultrasonication process, noble metal precursors could be co‐reduced by chemical reductants and transform to alloy structures under operation at room conditions. The instantaneous massive energy (≈5000 °C, 2000 atm) occurring in momentary timespans (≤10−9 s) contributes to the formation of multimetallic mixed nanomaterials driven by entropy maximization. Owing to strong synergistic effects, the catalysts with the HEA NPs supported on carbons exhibit prominent electrocatalytic activities for hydrogen evolution reaction.

Colloidal suspensions of AuPt alloy nanoparticles (NPs) were prepared by using a rapid butyllithium reduction of Au3+ and Pt4+ precursors in oleylamine. The resulting 2.5 nm (av) particles were characterized by TEM with EDX, XRD, XPS and UV‐vis spectroscopy. With less butyllithium, nanowires are formed from fused NPs and grow to 100 nm in length. The activities of three different AuPt NP architectures (alloy, contact aggregate and monometallic NPs) were evaluated for catalytic hydrogen oxidation in CO‐contaminated fuel streams (1.0 % Pt loadings in Al2O3 supports). The alloy catalyst showed superior H2 and CO oxidation activity, was unaffected by iron promoters and appears to operate by a different mechanism. The heteroaggregate showed a marked improvement in activity with iron promoters and is more selective for CO oxidation.

Gold nanoparticles (Au NPs) were prepared by reducing HAuCl 4 with NaBH 4 . Their average particle sizes could be tuned in the range of 1.7 and 8.2 nm, by adjusting the amount of NaBH 4 used during synthesis. The obtained Au NPs (colloids) were then loaded onto a commercial Al 2 O 3 support to prepare Au/Al 2 O 3 catalysts with tunable Au particle sizes. An optimal pH value (5.9) of the Au colloid solution was found to be essential for loading Au NPs onto Al 2 O 3 while avoiding the growth of Au NPs. Au NPs and Au/Al 2 O 3 catalysts were tested in the reduction of p-nitrophenol with NaBH 4 . Interestingly, the catalytic activity depended on the size of Au NPs, being the highest when the average size was 3.4 nm. Relevant characterization by UV-Vis, TEM, and XRD was conducted.

We report the synthesis of NiAu alloy nanoparticles (NPs) and their use in preparing Au/NiO CO oxidation catalysts. Because of the large differences in Ni and Au reduction potentials and the immiscibility of the two metals at low temperatures, [1,2] NiAu alloy NP colloids are inherently difficult to prepare by reducing metal salts with common reducing agents. This study describes the first solution-based synthesis of NiAu alloy NPs by way of a fast butyllithium reduction method. By supporting the particles on SiO 2 and subsequent conditioning, one obtains a NiO-stabilized Au NP catalyst that exhibits remarkable resistance to sintering and is highly active for CO oxidation. The active NiO-stabilized Au NP catalyst is prepared by in situ phase transformation of NiAu alloy NPs through an Au@Ni core-shell-like NP intermediate. In contrast, the corresponding NiO-free Au NPs prepared by an analogous method show negligible low-temperature catalytic activity and a high propensity for coalescence.The development of new bimetallic NP catalysts in various architectures (e.g. alloy, core-shell, aggregates) is receiving increased attention due to the need for more sophisticated, multifunctional catalysts in a variety of applications. [3][4][5][6][7] In comparison to monometallic systems, bimetallic catalysts have the potential advantages of bifunctional activity [8] (e.g. PtRu electrocatalysts), tunable non-native reactivities [5] (e.g. core-shell NPs), and stabilizing influences from a co-metal partner. A classic example of the later is to use certain metal oxides to modify "inactive" silica supports [9] to stabilize and activate small Au NPs for CO oxidation reactions. [10,11] To rationally advance the design of heterogeneous catalysts, systematic analyses of bimetallic architectures and the development of new synthetic methods to make multifunctional catalysts are needed. Herein, we report a new strategy to prepare oxide-stabilized noblemetal NP catalysts using a controlled stepwise phase-separation process of a bimetallic NP precursor. We demonstrate this strategy by making silica-supported NiO-stabilized Au CO oxidation catalysts using an in situ phase separation process of NiAu alloy NP precursor. Because silica is well known to be a poor support for stabilizing Au NPs in catalytic systems, it is an ideal support for evaluating effects of secondary metal oxide components.In the solid state, NiAu alloys can be prepared by high-temperature annealing. [1,2] However, this method produces large particles with small surface areas that limit their application in catalysis. The Ni-Au phase diagram [1,2] shows a solid-solution fcc alloy phase at high temperatures (> 740 8C for 1:1 alloy), but there is a large immiscibility region containing phase-separated fcc Au and fcc Ni at low temperatures. The low-temperature immiscibility of Ni and Au and the large discrepancy in reduction potentials complicate solution-based NiAu alloy preparations. In a previous report, we described a fast butyllithium reduction method for the preparatio...

The nature and role of different Au species on a Au/SiO 2 catalyst in room temperature (rt) CO oxidation have been studied by operando diffuse reflectance infrared spectroscopy (DRIFT) coupled with quadruple mass spectrometry (QMS). It has shown that different pretreatments (oxidative and reductive) of Au/SiO 2 have a significant effect on the nature of Au species and thus the CO oxidation performance. High temperature (500°C) O 2 -treatment leads to cationic Au species which is inactive for rt CO oxidation. Reductive treatment (either H 2 or CO) results in metallic Au species that are immediately active for rt CO oxidation. Furthermore, CO oxidation activity is found in good correlation with the reduction degree of Au species, a clear indication of the essential role of metallic Au species played in rt CO oxidation. The accompanying slight deactivation with the oxidation of metallic Au species on reductively treated Au/SiO 2 in CO oxidation suggests that cationic Au species may play a negative role in rt CO oxidation. The effect of water in rt CO oxidation on Au/SiO 2 was also investigated. Two positive roles played by water in CO oxidation have been identified: activation of O 2 and assistance the reduction of cationic Au species.

Tungsten-doped mesoporous KIT-6 (W-KIT-6), mesoporous silica supported WO 3 /KIT-6, and traditional silica supported WO 3 /SiO 2 catalysts have been successfully synthesized and tested for catalytic metathesis of 1-butene and ethene to propene. The resultant materials were comprehensively characterized by XRD, BET, TEM, UV−DRS, IR, XPS, H 2 -TPR, and TGA. For W-KIT-6 catalysts, high concentration of W 5+ species by XPS and the difficulty of reduction of W species by TPR suggested the incorporation of W species into the KIT-6 framework. The studies of smallangle XRD, BET, and TEM illustrated that the 3D ordered mesoporous structure and their high surface area of KIT-6 were maintained in W-KIT-6. The doped W-KIT-6 illustrated superior catalytic performance to the supported WO 3 /KIT-6 and WO 3 /SiO 2 catalysts. The origin of catalytic performance enhancement for W-KIT-6 was preliminarily discussed and was assigned to the incorporation of W species into KIT-6 framework. This study demonstrated the influence of neighboring environment of active components on catalytic performance and was helpful to design metathesis catalysts.