Understanding and controlling the structure and segregation behaviour of AuRh nanocatalysts

Heterogeneous catalysis, which is widely used in the chemical industry, makes a great use of supported late-transition-metal nanoparticles, and bimetallic catalysts often show superior catalytic performances as compared to their single metal counterparts. In order to optimize catalyst efficiency and discover new active combinations, an atomic-level understanding and control of the catalyst structure is desirable. In this work, the structure of catalytically active AuRh bimetallic nanoparticles prepared by colloidal methods and immobilized on rutile titania nanorods was investigated using aberration-corrected scanning transmission electron microscopy. Depending on the applied post-treatment, different types of segregation behaviours were evidenced, ranging from Rh core – Au shell to Janus via Rh ball – Au cup configuration. The stability of these structures was predicted by performing density-functional-theory calculations on unsupported and titania-supported Au-Rh clusters; it can be rationalized from the lower surface and cohesion energies of Au with respect to Rh, and the preferential binding of Rh with the titania support. The bulk-immiscible AuRh/TiO₂ system can serve as a model to understand similar supported nanoalloy systems and their synergistic behaviour in catalysis.

Clean Transformation of Ethanol to Useful Chemicals. The Behavior of a Gold-Modified Silicalite Catalyst

Upon addition of gold to silicalite-1 pellets (a MFI-type zeolite), the vapor phase oxidation of ethanol could be addressed to acetaldehyde or acetic acid formation. By optimizing the catalyst composition and reaction conditions, the conversion of ethanol could be tuned to acetaldehyde with 97% selectivity at 71% conversion or to acetic acid with 78% selectivity at total conversion. Considering that unloaded silicalite-1 was found to catalyze the dehydration of ethanol to diethylether or ethene, a green approach for the integrated production of four important chemicals is herein presented. This is based on renewable ethanol as a reagent and a modular catalytic process.

Au-Based Catalysts: Electrochemical Characterization for Structural Insights

Au-based catalysts are widely used in important processes because of their peculiar characteristics. The catalyst performance depends strongly on the nature and structure of the metal nanoparticles, especially in the case of bimetallic catalysts where synergistic effects between the two metals can be occasionally seen. In this paper, it is shown that electrochemical characterisation (cyclovoltammetry CV and electrochemical impedance spectroscopy EIS) of AuPd systems can be used to determine the presence of an electronic interaction between the two metals, thus providing a strong support in the determination of the nature of the synergy between Au and Pd in the liquid phase oxidation of alcohols. However, it seems likely that the strong difference in the catalytic behavior between the single metals and the bimetallic system is connected not only to the redox behaviour, but also to the energetic balance between the different elementary steps of the reaction.

Crystal structure of a Pd4 carbonyl tri-phenyl-phosphane cluster [Pd4(CO)5(PPh3)4]·2C4H8O, comparing solvates

Attempts to synthesize Au-Pd heterometallic compounds from homonuclear palladium or gold complexes, [Pd(PtBu2)2] and [Au(PPh3)Cl] in a tetra-hydro-furan (THF) solution under a CO atmosphere resulted in a homonuclear Pd cluster, namely penta-kis-(μ-carbonyl-κ(2) C:C)tetra-kis-(tri-phenyl-phosphane-κP)tetrapalladium(5 Pd-Pd) tetra-hydro-furan disolvate, [Pd4(CO)5(C18H15P)4]·2C4H8O. The complex mol-ecule lies on a twofold rotation axis. The crystal structure is described in relation to the CH2Cl2 solvate previously determined by our group [Willocq et al. (2011 ▸). Inorg. Chim. Acta, 373, 233-242], and in particular to the desolvated structure [Feltham et al. (1985 ▸). Inorg. Chem. 24, 1503-1510]. It is assumed that the title compound transforms into the latter structure, upon gradual loss of solvent mol-ecules. In the title compound, the symmetry-unique THF solvent mol-ecule is linked to the complex mol-ecule by a weak C-H⋯O hydrogen bond. Contributions of disordered solvent molecules to the diffraction intensities, most likely associated with methanol, were removed with the SQUEEZE [Spek (2015). Acta Cryst. C71, 9-18] algorithm.

Supported bimetallic nano-alloys as highly active catalysts for the one-pot tandem synthesis of imines and secondary amines from nitrobenzene and alcohols

All-in-one: supported nanoalloys as efficient heterogeneous catalysts for the one-pot synthesis of imines and secondary amines directly from nitrobenzene and benzylic alcohols using a hydrogen auto transfer strategy.

Macroporous TiO2encapsulated Au@Pd bimetal nanoparticles for the photocatalytic oxidation of alcohols in water under visible-light

A novel macroporous photocatalyst Au@Pd@TiO₂has been reported and showed excellent catalytic activity and stability in the aerobic oxidation of alcohols in water at ambient temperature when using air as the oxidizing agent under visible light irradiation.

Highly efficient Ni–Co oxide nanoparticles on nitrogen-doped FDU-15 for aerobic benzyl alcohol oxidation

Transition bimetal (Ni, Co) oxide nanoparticles immobilized onto nitrogen-doped FDU-15 are high active and show excellent selectivity to the benzaldehyde for the oxidation of benzyl alcohol.

Selective Cu4Pd alloy nanoparticles anchoring on amine functionalized graphite nanosheets and their use as reusable catalysts for a C–C coupling reaction with the sacrificial role of Cu for Pd-regeneration

Cu₄Pd nanoparticles have been anchored on amine functionalized graphite nanosheets and the composite has been used in C–C coupling with a sacrificial role of Cu for regeneration of metallic Pd.

Characterisation of gold catalysts

Au-based catalysts have established a new important field of catalysis, revealing specific properties in terms of both high activity and selectivity for many reactions.

Catalytic Gas-Phase Glycerol Processing over SiO2-, Cu-, Ni- and Fe- Supported Au Nanoparticles

In this study, we investigated different metal pairings of Au nanoparticles (NPs) as potential catalysts for glycerol dehydration for the first time. All of the systems preferred the formation of hydroxyacetone (HYNE). Although the bimetallics that were tested, i.e., Au NPs supported on Ni, Fe and Cu appeared to be more active than the Au/SiO₂ system, only Cu supported Au NPs gave high conversion (ca. 63%) and selectivity (ca. 70%) to HYNE.

Generation of catalytically active materials from a liquid metal precursor

A facile route to prepare catalytically active materials from a liquid metal alloy is introduced. Sonication of liquid galinstan (GaInSn) in alkaline solution or treating it with reducing agents generates In : Sn rich microspheres that are catalytically active for electron transfer reactions such as potassium ferricyanide and 4-nitrophenol reduction.

Gas phase selective hydrogenation over oxide supported Ni–Au

Ni–Au synergism on Al₂O₃ and TiO₂ generates increased surface reactive hydrogen with elevated reaction rates in the hydrogenation of nitroarenes.

AuRu/AC as an effective catalyst for hydrogenation reactions

AuRu bimetallic catalysts have been prepared by sequential deposition of Au on Ru or vice versa obtaining different nanostructures: when Ru has been deposited on Au, a Au_core–Ru_shell has been observed, whereas the deposition of Au on Ru leads to a bimetallic phase with Ru enrichment on the surface.

Metastable alloy nanoparticles, metal-oxide nanocrescents and nanoshells generated by laser ablation in liquid solution: influence of the chemical environment on structure and composition

Metastable nanoalloys, metal-oxide nanocrescents and metal@oxide nanoshells are generated by laser ablation in liquid solution (LASiS).

Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

The versatile role of PVP in nanoparticle synthesis is discussed in this Perspective article.