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29. Challenging Thermodynamics: Hydrogenation of Benzene to 1,3-Cyclohexadiene by Ru@Pt Nanoparticles.

Author

Weilhard, Andreas, Abarca, Gabriel, Viscardi, Janine, Prechtl, Martin H. G., Scholten, Jackson D., Bernardi, Fabiano, Baptista, Daniel L., and Dupont, Jairton

Subjects
HYDROGENATION, BENZENE, CYCLOHEXADIENE, NANOPARTICLES, CYCLOHEXENE
Abstract

Since the earliest reports on catalytic benzene hydrogenation, 1,3-cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein, we report the first partial hydrogenation of benzene towards 1,3-cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2-methylallyl)2] (COD=1,5-cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba=dibenzylideneacetone) in 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMI ⋅PF6) IL under hydrogen affords core-shell Ru@Pt NPs of 2.9±0.2 nm. The hydrogenation of benzene (60 °C, 6 bar of H2) dissolved in n-heptane by these bimetallic NPs in BMI ⋅PF6 affords 1,3-cyclohexadiene with an unprecedented 21 % selectivity at 5 % benzene conversion. Conversely, almost no 1,3-cyclohexadiene was observed when using monometallic Pt0 or Ru0 NPs under the same reaction conditions and benzene conversions. This study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as to the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions ('dynamic asymmetric mixtures') can operate far from the thermodynamic equilibrium akin to chemically active membranes. [ABSTRACT FROM AUTHOR]

Published
2017
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36. Synergizing nanocomposites of CdSe/TiO2 nanotubes for improved photoelectrochemical activity via thermal treatment.

Author

Fernandes, Jesum A., Khan, Sherdil, Baum, Fabio, Kohlrausch, Emerson C., Lucena dos Santos, José Augusto, Baptista, Daniel L., Teixeira, Sergio R., Dupont, Jairton, and Santos, Marcos J. Leite

Subjects
MAGNETRON sputtering, NANOCOMPOSITE materials, SCANNING electron microscopy, RUTHERFORD backscattering spectrometry, X-ray diffraction
Abstract

In this work, we show the effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO2 nanocomposites. TiO2 nanotubes (NTs) were synthesized by anodization and the nanocomposites were obtained by depositing CdSe clusters via magnetron sputtering. A two-step thermal treatment was performed: heating the TiO2 NTs at different temperatures prior to CdSe deposition and further heating the CdSe/TiO2 nanocomposites. The nanocomposites were characterized by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-Vis spectrophotometry, and electrochemical impedance spectroscopy (EIS). To compare the PEC performance of the CdSe/TiO2 nanocomposites and pristine TiO2 NTs, linear sweep voltammetry (LSV) curves were obtained under visible light and under 1 sun illumination. It was observed that CdSe incorporation into the TiO2 template enhances the visible light absorbance thereby improving the PEC performance of the nanocomposites. We have found that the optical, structural and PEC properties of the CdSe/TiO2 nanocomposites are dependent on the thermal treatment temperature of the TiO2 nanotubular substrate, prior to CdSe deposition. Moreover, a three-fold improvement in photocurrent was observed upon further thermal treatment of the obtained nanocomposite. [ABSTRACT FROM AUTHOR]

Published
2016
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37. Iron Particle Nanodrilling of Few Layer Graphene at Low Electron Beam Accelerating Voltages

Author

Campos-Delgado, Jessica, primary, Baptista, Daniel L., additional, Fuentes-Cabrera, Miguel, additional, Sumpter, Bobby G., additional, Meunier, Vincent, additional, Terrones, Humberto, additional, Kim, Yoong Ahm, additional, Muramatsu, Hiroyuki, additional, Hayashi, Takuya, additional, Endo, Morinobu, additional, Terrones, Mauricio, additional, and Achete, Carlos A., additional

Published
2012
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38. Nanodrilling: Iron Particle Nanodrilling of Few Layer Graphene at Low Electron Beam Accelerating Voltages (Part. Part. Syst. Charact. 1/2013)

Author

Campos-Delgado, Jessica, primary, Baptista, Daniel L., additional, Fuentes-Cabrera, Miguel, additional, Sumpter, Bobby G., additional, Meunier, Vincent, additional, Terrones, Humberto, additional, Kim, Yoong Ahm, additional, Muramatsu, Hiroyuki, additional, Hayashi, Takuya, additional, Endo, Morinobu, additional, Terrones, Mauricio, additional, and Achete, Carlos A., additional

Published
2012
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39. Geometric and Electronic Structure of Closed Graphene Edges

Author

Lopez-Bezanilla, Alejandro, primary, Campos-Delgado, Jessica, additional, Sumpter, Bobby G., additional, Baptista, Daniel L., additional, Hayashi, Takuya, additional, Kim, Yoong A., additional, Muramatsu, Hiroyuki, additional, Endo, Morinobu, additional, Achete, Carlos A., additional, Terrones, Mauricio, additional, and Meunier, Vincent, additional

Published
2012
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40. Influence of the CeO2Support on the Reduction Properties of Cu/CeO2and Ni/CeO2Nanoparticles

Author

Matte, Lívia P., Kilian, Alex S., Luza, Leandro, Alves, Maria C. M., Morais, Jonder, Baptista, Daniel L., Dupont, Jairton, and Bernardi, Fabiano

Abstract

Ceria (CeO2) is being increasingly used as support of metallic nanoparticles in catalysis due to its unique redox properties. Shedding light into the nature of the strong metal support interaction (SMSI) effect in CeO2-containing catalysts is important since it has a strong influence on the catalytic properties of the system. In this work, Cu/CeO2and Ni/CeO2nanoparticles are characterized when submitted to a reduction treatment at 500 °C in H2atmosphere with a combination of in situ (XAS – X-ray absorption spectroscopy and time-resolved XAS) and ex situ (TEM – transmission electron microscopy and XPS - X-ray photoelectron spectroscopy) techniques. The existence of a capping layer decorating the Ni/CeO2nanoparticles after the reduction treatment is shown, representing evidence for the SMSI effect. The kinetics of the SMSI occurrence is elucidated. It is proposed that the electronic factor of the SMSI effect has a strong influence on the reduction properties of the Ni nanoparticles supported on CeO2, decreasing its reduction temperature if compared to nonsupported Ni nanoparticles. The same phenomenon is not observed for Cu/CeO2nanoparticles, where there is no evidence for the SMSI effect, and no changes on the reduction properties between supported and nonsupported Cu nanoparticles are observed.

Published
2015
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43. On the Structural and Chemical Characteristics of Co/Al2O3/graphene Interfaces for Graphene Spintronic Devices.

Author

Canto, Bárbara, Gouvea, Cristol P., Archanjo, Bráulio S., Schmidt, João E., and Baptista, Daniel L.

Subjects
INTERFACES (Physical sciences), GRAPHENE, COBALT, ALUMINUM oxide, DIFFUSION
Abstract

We report a detailed investigation of the structural and chemical characteristics of thin evaporated Al2O3 tunnel barriers of variable thickness grown onto single-layer graphene sheets. Advanced electron microscopy and spectrum-imaging techniques were used to investigate the Co/Al2O3/graphene/SiO2 interfaces. Direct observation of pinhole contacts was achieved using FIB cross-sectional lamellas. Spatially resolved EDX spectrum profiles confirmed the presence of direct point contacts between the Co layer and the graphene. The high surface diffusion properties of graphene led to cluster-like Al2O3 film growth, limiting the minimal possible thickness for complete barrier coverage onto graphene surfaces using standard Al evaporation methods. The results indicate a minimum thickness of nominally 3 nm Al2O3, resulting in a 0.6 nm rms rough film with a maximum thickness reaching 5 nm. [ABSTRACT FROM AUTHOR]

Published
2015
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45. Photo-induced reforming of alcohols with improved hydrogen apparent quantum yield on TiO2 nanotubes loaded with ultra-small Pt nanoparticles.

Author

Languer, Mariana P., Scheffer, Francine R., Feil, Adriano F., Baptista, Daniel L., Migowski, Pedro, Machado, Guilherme J., de Moraes, Diogo P., Dupont, Jairton, Teixeira, Sérgio R., and Weibel, Daniel E.

Subjects
*ALCOHOLS (Chemical class), *CATALYTIC reforming, *PHOTOCHEMISTRY, *HYDROGEN production, *NANOTUBES, *TITANIUM dioxide nanoparticles
Abstract

Abstract: Photo-induced reforming of methanol, ethanol, glycerol and phenol at room temperature for hydrogen production was investigated with the use of ultra-small Pt nanoparticles (NPs) loaded on TiO2 nanotubes (NTs). The Pt NPs with diameters between 1.1 and 1.3 nm were deposited on TiO2 NTs by DC-magnetron sputtering (DC-MS) technique. The photocatalytic hydrogen rate achieved an optimum value for a loading of about 1 wt% of Pt. Apparent quantum yield for hydrogen generation was measured for methanol and ethanol water solutions reaching a maximum of 16% under irradiation with a wavelength of 313 nm in methanol/water solution (1/8 v/v). Pt NPs loaded on TiO2 NTs represented also a true water splitting catalyst under UV irradiation and pure distilled water. DC-MS method appears to be a technologically simple, ecologically benign and potentially low-cost process for production of an efficient photocatalyst loaded with ultra-small NPs with precise size control. [Copyright &y& Elsevier]

Published
2013
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