Dario Eberhardt

“Imprinting” Catalytically Active Pd Nanoparticles onto Ionic-Liquid-Modified Al2O3 Supports

A new sputtering chamber that allows the constant mixing of the solid support during sputtering by using an electro-magnetic oscillator was developed for the generation of metal nanoparticles (top down approach) uniformly distributed over the solid supports. By using this new chamber, small and welldistributed Pd nanoparticles (Pd-NPs) of 2.6 or 4.3 nm were produced over Al2O3 and new imidazolium ionic liquids covalently supported on Al2O3 by simple sputtering from a Pd foil. The Pd-NPs uniformly distributed over the solid supports display comparable catalytic performances in the hydrogenation of 1,3-cyclohexadiene and 1,3-cyclooctadiene to that achieved by using a catalyst prepared by conventional chemical methods (bottom up approach). Mechanistic and labelling studies show that the hydrogenation of 1,3-cyclohexadiene catalysed by Pd-NPs occurs via meta-stable p-allyl intermediates, characteristic of homogeneous-like catalytically active sites, and disproportionation through the outer-sphere mechanism. The ratio of hydrogenation to disproportionation is dependent on the Pd-NP size, and the disproportionation products are more pronounced with small NPs because of the higher affinity of dienes for this size of particle. Therefore, the surface structural features of small Pd-NPs facilitate the arrangement of diene molecules in the correct geometry for the transfer of H from the donor to the acceptor sites, typical of poly-metallic catalytically active sites. It is proposed that the reaction of 1,3-cyclohexadiene under H2 can be used to probe the homogeneous/ heterogeneous nature of supported metal NPs. It is demonstrated for the first time that highly active and selective nanocatalysts were obtained by using the sputtering-deposition technique (top down approach) and this opens a new window of opportunity for the preparation of size-controlled metal NPs with clean surfaces. Introduction

Easy Access to Metallic Copper Nanoparticles with High Activity and Stability for CO Oxidation.

Copper catalysts are very promising, affordable alternatives for noble metals in CO oxidation; however, the nature of the active species remains unclear and differs throughout previous reports. Here, we report the preparation of 8 nm copper nanoparticles (Cu NPs), with high metallic content, directly deposited onto the surface of silica nanopowders by magnetron sputtering deposition. The as-prepared Cu/SiO2 contains 85% Cu0 and 15% Cu2+ and was enriched in the Cu0 phase by H2 soft pretreatment (96% Cu0 and 4% Cu2+) or further oxidized after treatment with O2 (33% Cu0 and 67% Cu2+). These catalysts were studied in the catalytic oxidation of CO under dry and humid conditions. Higher activity was observed for the sample previously reduced with H2, suggesting that the presence of Cu-metal species enhances CO oxidation performance. Inversely, a poorer performance was observed for the sample previously oxidized with O2. The presence of water vapor caused only a small increase in the temperature require for the reaction to reach 100% conversion. Under dry conditions, the Cu NP catalyst was able to maintain full conversion for up to 45 h at 350 °C, but it deactivated with time on stream in the presence of water vapor.

Hybrid tantalum oxide nanoparticles from the hydrolysis of imidazolium tantalate ionic liquids: efficient catalysts for hydrogen generation from ethanol/water solutions

The reaction of equimolar amounts of 1-n-butyl-3-methylimidazolium chloride (BMI·Cl) or 1-n-decyl-3-methylimidazolium chloride (DMI·Cl) with TaCl5 affords imidazolium tantalate ionic liquids (ILs) BMI·TaCl61 and DMI·TaCl62. The hydrolysis of ILs 1 and 2 yields hybrid-like tantalum oxide nanoparticles (NPs) with size distribution dependent on the nature of the IL used (3.8–22 nm from IL 1 and 1.5–6 nm from 2). A significant aggregation/agglomeration of the particles was observed after the removal of the IL content of the hybrid material by calcination, forming predominantly large particles (mainly bulk tantalum oxides). These new hybrid-like Ta2O5/IL NPs are highly active photocatalyst nanomaterials for hydrogen production by reforming of ethanol at ambient temperature. Hydrogen evolution rates up to 7.2 mmol H2 g−1 h−1 and high apparent quantum yields up to 17% were measured. The hybrid-like Ta2O5/IL NPs sputtered-decorated with ultra-small Pt NPs (1.0 ± 0.3 nm) as co-catalysts reached activities leading to even higher hydrogen production (9.2 H2 mmol g−1 h−1; apparent quantum yield of 22%). The calcined materials (with or without Pt NPs) showed much lower photocatalytic activity under the same reaction conditions (up to 2.8 mmol g−1 of H2). The remarkable activity of the hybrid-like Ta2O5/IL NPs may be related to the presence of the remaining IL that provides hydrophilic regions, facilitating the approach of polar molecules (water and alcohol) to the semiconductor active photocatalytic sites.

Templated Growth of Pd Nanoparticles Using Sputtering Deposition Process and Its Catalytic Activities

A simple method based on sputtering deposition of Pd onto mesoporous SiO2 (SBA-15) was employed to produce supported Pd nanoparticles (NPs) that can be used as hydrogenation catalysts. The use of sputtering deposition eliminates contaminants and avoids additional drawbacks of traditional chemical methods applied to prepare heterogeneous supported metal catalysts. A mechanical resonant stirrer was used to revolve the SBA-15 powder and ensure homogeneous distribution of the Pd NPs over the support. The SBA-15 pores act as templates for Pd NPs and drive nanostructure growth. Consequently, the NPs obtained have the same diameter as that of the SBA-15 channels (~5 nm) and elongated particles are formed as sputtering deposition increases. The SBA-15 supported Pd NPs (Pd NPs/SBA-15) were tested in a probe hydrogenation of cyclohexene reaction to evaluate the catalytic activity of the Pd NPs. Turnover frequency (TOF) of 2000 min-1 were achieved with the lower Pd NPs concentration (0.15 wt%) catalyst.