The combination of two or more metals, forming alloys, core−shells, or other complex heterometallic nanostructures, has substantially spanned the available options to finely tune electronic and structural properties, opening a myriad of opportunities that has yet to be fully explored in different fields. In catalysis, the rational exploitation and design of bimetallic and trimetallic catalysts has just started. Several major aspects such as stability, phase segregation, and alloy− dealloy mechanisms have yet to be deeply understood and correlated with intrinsic factors such as nanoparticle size, composition, and structure and with extrinsic factors, or external agents, such as temperature, reaction gases, and support. Here, by combining model catalysts based on AuCu nanoparticles supported on silica or alumina with in situ characterization techniques under redox pretreatments and CO oxidation reaction, we demonstrate the crucial role of the support with regard to determining the stable active phase of bimetallic supported catalysts. This strategy, associated with theoretical studies, could lead to the rational design of unique active sites.

Metal-terminated bimetallic carbide nanoparticles (NPs) of tungsten and tantalum are synthesized in a monodisperse particle size distribution of 2–3 nm. The bimetallic particles feature enhanced electrocatalytic behavior with respect to the monometallic composition. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements indicate that the Ta0.3W0.7C NPs consist of a well-mixed random alloy featuring a compressed lattice that favorably impacts stability and catalytic activity. Electrochemical testing shows that the incorporation of 30% tantalum into the tungsten carbide lattice increases the electrochemical oxidation resistance of the NPs. The onset of surface passivation in 0.5 M H2SO4 shifted from +0.2 V vs RHE to +0.45 V vs RHE, and the maximum surface oxidation current shifted from +0.4 to +0.75 V vs RHE. The activity toward hydrogen evolution (HER) of the carbon-supported Ta0.3W0.7C NPs is preserved relative to the activity of unmodified carbon-supported WC NPs. The increase in electrochemical oxidation resistance is attributed to the presence of surface Ta moieties as determined by X-ray photoelectron spectroscopy (XPS) while the preservation of the HER activity is attributed to the observed lattice compression.

We report the colloidal synthesis of dumbbell-like AuCu@FeO nanocrystals (AuCu@FeOx NCs) and the study of their properties in the CO oxidation reaction. To this aim, the as-prepared NCs were deposited on γ-alumina and pretreated in an oxidizing environment to remove the organic ligands. A comparison of these NCs with bulk FeO-supported AuCu NCs showed that the nanosized support was far more effective in preventing the sintering of the metal domains, leading thus to a superior catalytic activity. Nanosizing of the support could be thus an effective, general strategy to improve the thermal stability of metallic NCs. On the other hand, the support size did not affect the chemical transformations experienced by the AuCu NCs during the activation step. Independently from the support size, we observed indeed the segregation of Cu from the alloy phase under oxidative conditions as well as the possible incorporation of the Cu atoms in the iron oxide domain.

Ru nanocrystals supported on vertically oriented copper nanoplates are developed as a hydrogen evolution catalyst in alkaline media. This catalyst outperformed benchmark Pt/C in terms of activity and stability.

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