Monodisperse Au nanoparticles (NPs) have been synthesized at room temperature via a burst nucleation of Au upon injection of the reducing agent t-butylamine-borane complex into a 1, 2, 3, 4-tetrahydronaphthalene solution of HAuCl 4 ·3H 2 O in the presence of oleylamine. The as-synthesized Au NPs show size-dependent surface plasmonic properties between 520 and 530 nm. They adopt an icosahedral shape and are polycrystalline with multiple-twinned structures. When deposited on a graphitized porous carbon support, the NPs are highly active for CO oxidation, showing 100% CO conversion at -45 °C.

Heterogeneous dumbbell-like nanoparticles represent an important type of composite nanomaterial that has attracted growing interest. Here we report a general approach to noble metal−metal oxide dumbbell nanoparticles based on seed-mediated growth. Metal oxides are grown over the presynthesized noble metal seeds by thermal decomposition of metal carbonyl followed by oxidation in air. The as-synthesized dumbbell nanoparticles have intrinsic epitaxial linkage between the metal and the oxide, providing enhanced heterojunction interactions. Moreover, the properties of one component are readily modified by the other in these nanoparticles, as demonstrated by the enhanced catalytic activity toward CO oxidation of such dumbbell nanoparticles in comparison with their counterparts prepared by conversional methods. The heterojunction effects provided in such nanostructures thus offer another degree of freedom for tailoring material properties. The developed synthetic strategy could also be generalized to other systems and thus represent a general approach to heterogeneous nanomaterials for various functional applications.

Monodisperse AuAg alloy NPs were synthesized by a one-pot approach with composition control. Oleylamine was used as the surfactant and was readily removed. The AuAg alloy NPs show the compositional dependent plasmonic absorptions and catalytic CO oxidation, indicating their great potentials as optical probes for bioimaging and as active catalyst for chemical reactions.

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...

Highly active Au catalysts with a dumbbell-like heterostructure for CO oxidation were prepared through colloidal deposition method; both activities and stabilities were investigated under different experimental conditions.

Oxides and carbon are commonly used as supports for gold nanoparticles, but metal salts are barely considered as suitable supports. Our group recently communicated that gold nanoparticles supported on nanosized LaPO 4 (6-8 nm) are active for CO oxidation (Yan et al., Angew Chem Int Ed 45:3614, 2006). In the current work, we systematically developed an array of Au/M-P-O catalysts and tested them for catalytic activity and stability. It was found that 200°C-pretreated Au/M-P-O (M = Ca, Fe, Co, Y, La, Pr, Nd, Sm, Eu, Ho, Er) show high CO conversions below 50°C, and 500°C-pretreated Au/M-P-O (M = Ca, Y, La, Pr, Nd, Sm, Eu, Ho, Er) show high CO conversions below 100°C. These samples were characterized by ICP-OES, BET, XRD, TEM, SEM, and H 2 -TPR. The stability of selected catalysts was studied as a function of time on stream. This work furnishes a new catalyst system for further fundamental and applied research.

Pd@SiO2 core–shell nanoparticles were successfully synthesized by a sol–gel method. Tetradecyl trimethyl ammonium bromide capped Pd nanoparticles were coated with SiO2 through the hydrolysis of tetraethylorthosilicate. The as-synthesized Pd@SiO2 particles consist of Pd cores with a particle size of 3.7 nm and SiO2 shells with a thickness from 10 to 30 nm at different synthetic conditions. The Pd@SiO2 nanocatalysts with 1.9–2.4 nm mesoporous SiO2 shells were generated after removal of tetradecyl trimethyl ammonium bromide from Pd@SiO2 core–shell particles by calcination and following H2 reduction. The relevant characterizations such as XRD, TEM, FT-IR, and BET were carried out for Pd@SiO2 particles, and the results showed that the Pd@SiO2 nanocatalysts were highly stable with the protection of silica shells, and the Pd cores did not increase during thermal treatment and H2 reduction. The studies of catalytic CO oxidation at high temperatures and hydrogenation of nitrobenzene with H2 were tested for Pd@SiO2 nanocatalysts, and the results indicated that Pd@SiO2 nanocatalysts were stable at high temperatures and highly active and stable for hydrogenation of nitrobenzene even after long time use.

In this work, Pt-SnO2 heteroaggregate nanocatalysts were synthesized by in situ transformation of Pt@Sn core–shell nanoparticles and their catalytic performance for hydrogenation of various substituted nitroaromatics was investigated. The Pt@Sn nanoparticles were prepared by a one-step method, and the alumina-supported Pt@Sn nanoparticles were further transformed in situ into Pt-SnO2 heteroaggregate nanostructures by calcination. The structures of Pt@Sn and Pt-SnO2 nanomaterials were characterized, and FT-IR with CO probes, HRTEM, XRD, and XPS characterizations revealed that the as-synthesized Pt@Sn nanoparticles were core@shell-like structures with Sn-rich shells and Pt-rich cores and the obtained Pt-SnO2 heteroaggregate nanostructures consisted of close-contact pure Pt and SnO2 phases. The Pt-SnO2/Al2O3 nanostructures demonstrated a better catalytic performance for hydrogenation of various substituted nitroaromatics relative to individual Pt/Al2O3 nanocatalysts. Theoretical calculations suggested that Pt-SnO2 nanocatalysts can slightly facilitate the adsorption of H2 and o-chloronitrobenzene and strongly weaken the binding of Pt/o-chloroaniline, resulting in more available reactants and easier release of products from the catalyst surfaces. The theoretical calculations indicated that the enhanced catalytic performance may originate from a cooperative interaction between Pt and SnO2.