Freestanding tantalum oxide nanotubes (Ta 2 O 5 NTs) were easily fabricated by controlling only the electrolyte temperature during anodization in a sulfuric acid solution. When the electrolyte temperature decreased, the adherence of NTs to the Ta substrate increased. High electrolyte temperatures facilitated formation of freestanding NTs. Thermal treatment of the freestanding Ta 2 O 5 NTs below 750 °C resulted in an amorphous structure. The orthorhombic crystalline phase appeared only at temperatures higher than 750 °C. The effect of thermal treatment on the crystalline structure and morphology of Ta 2 O 5 NTs showed that the NTs retained their tubular shape up to 800 °C. In addition, it was shown that the crystallinity of the NTs was enhanced from 11% to 34% by increasing the treatment time for the NTs at 800 °C from 0.5 to 1 h. High crystallinity and low surface contamination increased the photocatalytic activity of the freestanding NTs for hydrogen production by water splitting using a water/ethanol solution under UV radiation. The sample annealed at 800 °C for 1 h showed the highest photocatalytic activity for hydrogen generation. Additionally, changes to the physicochemical properties of the surface and bulk of the photocatalyst showed decreased selectivity for minor products (C 2 H 4 and C 2 H 6 ).

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.

Going against tradition: Uniformly distributed Pd nanoparticles on imidazolium‐ionic‐liquid‐modified Al2O3 surfaces are prepared by a top down approach by using a new sputtering chamber. The hydrogenation of 1,3‐cyclohexadiene is used to probe the surface properties of these new Pd nanoparticles.

Hybrid organosilicas prepared by sol-gel processes using 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions can be easily decorated with well dispersed and similar size (1.8-2.1 nm) Pd nanoparticles (Pd-NPs) by simple sputtering-deposition. Higher Pd concentration at the surface compared to the deeper region is obtained in the supports with smaller pore diameter (containing hydrophobic ILs) than in supports with the largest pore diameter (containing hydrophilic ILs). The IL hydrophobicity plays a central role in the hydrogenation of dienes by controlling the diene access to NP surface active sites.

Gold nanoparticles (AuNPs) display distinct characteristics as hydrogenation catalysts, with higher selectivity and lower catalytic activity than group 8−10 metals. The ability of AuNPs to chemisorb/activate simple molecules is limited by the low coordination number of the surface sites. Understanding the distinct pathways involved in the hydrogenation reactions promoted by supported AuNPs is crucial for broadening their potential catalytic applications. In this study, we demonstrate that the mechanism of the hydrogenation reactions catalyzed by AuNPs with "clean" surfaces may proceed via homolytic or heterolytic hydrogen activation depending on the nature of the support. The synthesis of naked AuNPs employing γ-Al 2 O 3 and ionic liquid (IL)-hybrid γ-Al 2 O 3 supports was accomplished by sputtering deposition using ultrapure gold foils. This highly reproducible and straightforward procedure furnishes small (∼6.6 nm) and well-distributed metallic gold nanoparticles (Au(0)NPs) that are found to be active catalysts for the partial and selective hydrogenation of substituted conjugated dienes, alkynes, and α,β-unsaturated carbonyl compounds (aldehydes and ketones). Kinetic and deuterium labeling studies indicate that heterolytic hydrogen activation is the primary pathway occurring on the AuNPs imprinted directly on γ-Al 2 O 3 . In contrast, AuNPs supported on IL-hybrid γ-Al 2 O 3 materials cause the reaction to proceed via a homolytic hydrogen activation pathway. The IL layer surrounds the AuNPs and acts as a cage, influencing the frequency of the interaction of the catalytically active species and the metal surface and, consequently, the catalytic performance of the AuNPs. The IL layer is shown to improve the product selectivity by the enhancement of the substrate/product discrimination, and to decrease the catalytic activity by shifting the rate-determining step to the H 2 and substrate competitive adsorption/activation on the same active sites. A series of kinetic experiments suggest that AuNPs imprinted on an IL-hybrid γ-Al 2 O 3 support are more efficient (lower activation energy, E a ) than group 8−10 metal based catalysts for hydrogenation reactions at moderate to high temperatures (75−150°C).