Claudio Evangelisti

Supported Rhodium Nanoparticles in Catalysis: the role of stabilizers on catalytic activity and structural features

Abstract Rhodium nanoparticles supported on γ-Al 2 O 3 , derived from arene-solvated Rh atoms stabilized by trioctylamine (TOA), are valuable catalysts in hydrogenation and silylformylation reactions. They are largely more active than the analogous commercial catalyst, as well as of a sample similarly prepared in the absence of TOA. HRTEM measurements, IR studies on adsorbed CO species and extended X-ray absorption fine structure analyses evidenced the role of TOA in controlling the particle growth in the preparative process and in stabilizing the resulting Rh particles against erosion by CO and oxidation.

Gold nanoparticles obtained by aqueous digestive ripening: Their application as X-ray contrast agents

A preparative protocol to synthesize large quantities of size-controlled gold nanoparticles (Au NPs), stabilized by CH3O-PEG5000-SH (PEG-SH) in aqueous medium, is reported. The combination of metal vapor synthesis (MVS) technique with digestive ripening process allowed to obtain PEGylated Au NPs with mean core particle size of 3.8nm and hydrodynamic diameters centered at 8.0nm which were effectively used as computed tomography (CT) contrast agents for in vivo experiments on mice. The surface functionalization together with the small hydrodynamic diameters of the engineered Au nanoparticles permitted their efficient renal clearance, still retaining a prolonged blood circulation and a stealth capability.

Water Gas Shift Reaction in Pd-Based Membrane Reactors

Water-gas shift reaction is an important industrial reaction, used for producing synthesis gas and ammonia as well as pure hydrogen for supplying at PEM fuel cells. In this work, an overview on water gas shift reaction performed in Pd-based membrane reactors is shown, paying particular attention to the influence on the performances of some operating variables such as reaction temperature, reaction pressure, H2O/CO molar ratio and sweep gas.

Dehydrogenative coupling promoted by copper catalysts: a way to optimise and upgrade bio-alcohols

A process for the one-step transformation of butanol into butyl butyrate has been set up by using a copper/zirconia catalyst. Yields of up to 98% can be obtained at 250 °C by withdrawing the H2 formed. The high activity has been investigated through STEM analysis of the catalyst and FT IR spectroscopy of the substrate adsorbed on the catalyst surface.

Synthesis of Nanocrystalline TiOF2 Embedded in a Carbonaceous Matrix from TiF4 and D-Fructose.

Nanostructured titanium oxide difluoride embedded in a matrix of amorphous carbon was synthesized by pyrolysis of D-fructose in the presence of titanium tetrafluoride (optimal Ti/fructose molar ratio = 5.5), both in the solid state at ca. 150 °C and in suspension of 1,2-dichloroethane at reflux temperature. The resulting solid materials were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and elemental analysis. In every case, PXRD and TEM data indicated the presence of an unique crystalline phase (TiOF2) embedded in a light matrix (amorphous carbon). The average crystal size of the powder can be regulated by varying the reaction time.

Water soluble heptakis(6-deoxy-6-thio)cyclomaltoheptaose capped gold nanoparticles via metal vapour synthesis: NMR structural characterization and complexation properties.

The complexation of heptakis(6-deoxy-6-thio)cyclomaltoheptaose to gold nanoparticles prepared by using the Metal Vapour Synthesis (MVS) led to water soluble gold nanoaggregates, thermally stable at 25°C. The role of gold concentration in the MVS-derived starting solution as well as of the cyclodextrin to gold molar ratio on the size of cyclodextrin-capped gold nanoparticles were investigated. The ability of cyclodextrin bonded to gold nanoparticles to include deoxycytidine was also probed in comparison with that of 1-thio-β-D-glucose sodium salt.

EXAFS and XANES structural characterization of bimetallic AuPd vapor derived catalysts

Using an innovative procedure known as metal vapor synthesis (MVS) to prepare bimetallic catalysts, starting from Au and Pd vapors, [AuPd] co-evaporated and [Au][Pd] separately evaporated bimetallic catalysts were achieved. After being tested, the catalytic activity and selectivity of the [AuPd] catalyst turned out to be higher than the [Au][Pd] ones. Using EXAFS spectroscopy it was shown that, in the [AuPd] samples, small bimetallic AuPd nanoparticles were present, having an Au rich core surrounded by an AuPd alloyed shell while in the [Au][Pd] sample there was the presence of monometallic Au and Pd nanoparticles showing some alloying only in the boundary regions. The EXAFS results were also qualitatively confirmed by the XANES spectra.

Tailoring and stabilization of ultrafine rhodium nanoparticles on γ-Al2O3 by troctylamine: Dependence of the surface properties on the preparation route

Abstract Rhodium nanoparticles supported on γ-AI2O3 have been prepared by Metal Vapour Synthesis (MVS), using mesitylene solvated Rh atoms as starting material and working in the absence and in the presence of trioctylamine (TOA), as stabilizer. The size and surface features of the metal particles have been studied by Transmission Electron Microscopy (TEM) and by FT-IR spectroscopy of adsorbed carbon monoxide, and they have been compared with those of a commercial Rh/γ-AI2O3 sample. The results indicated that by MVS technique nanoparticles significantly smaller in size and with a narrower size distribution than those present on the commercial sample were produced. The addition of TOA during the MVS process resulted in a further decrease in the metal particle size. IR spectra of adsorbed CO indicated that metal particles produced via MVS expose at their surface a larger fraction of Rh atoms in low coordination. They can be extracted by CO, forming volatile Rh carbonyls which migrate onto the support, where the metal atoms are oxidised to Rh(I). For Rh particles produced via MVS in the presence of TOA, such low coordinated sites appeared stabilised by adsorbed amine molecules.

Fluidic Manufacture of Star-shaped Gold Nanoparticles

Star-shaped gold nanoparticles (StarAuNPs) are extremely attractive nanomaterials, characterized by localized surface plasmon resonance which could be potentially employed in a large number of applications. However, the lack of a reliable and reproducible synthetic protocols for the production of StarAuNPs is the major limitation to their spreading. For the first time, here we present a robust protocol to manufacture reproducible StarAuNPs by exploiting a fluidic approach. Star-shaped AuNPs have been synthesized by means of a seed-less protocol, employing ascorbic acid as reducing agent at room temperature. Moreover, the versatility of the bench-top microfluidic protocol has been exploited to afford hydrophilic, hydrophobic and solid-supported engineered StarAuNPs, by avoiding intermediate NP purifications.

Structural characterization of bimetallic Pd-Cu vapor derived catalysts

Pd-Cu bimetallic Solvated Metal Atoms (SMA) were synthesized by metal vapor synthesis technique and supported on PVPy resin. Since the catalytic activity, of the Pd-Cu system turned out to be quite high also compared to the corresponding monometallic system, a structural characterization, using electron microscopy techniques and X-ray Absorption Fine Structure spectroscopy, was performed. HRTEM analysis showed the presence of Pd particles distributed in a narrow range with a mean diameter of about 2.5 nm while the XAFS analysis, confirmed the presence of the Pd nanoparticles but revealed also some alloying with Cu atoms.