Thenner Rodrigues - Academia.edu (original) (raw)

Papers by Thenner Rodrigues

In the present work, coconut coal was activated by the microwave-assisted hydrothermal process (H... more In the present work, coconut coal was activated by the microwave-assisted hydrothermal process (HMO) using nitric acid (2.42 M) under the temperature conditions of 120 oC doe 45-minutes, heating rate of 10 oC / min and pressure of 3.0 kgf / cm 2. The samples were characterized by infrared spectroscopy, Raman spectroscopy, surface area measurements (BET), thermal gravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and temperature programmed reduction (TPR). The catalysts were evaluated in the ethanol steam reforming aiming the formation of hydrogen. Suitable catalytic activities were observed with complete conversion of ethanol and predominant formation of reforming products (H2 and CO2) and only CO and CH4 as by-products (both in low concentrations), indicating a good selectivity for the ethanol steam reforming reaction. The catalysts also showed good stabilities with high catalytic activity after 24 hours of r...

Gold (Au) nanoparticles are known to be highly active towards a wide variety of heterogeneous cat... more Gold (Au) nanoparticles are known to be highly active towards a wide variety of heterogeneous catalytic transformations, including oxidation, reduction, C-C coupling reactions, and others.1 Among these transformations, silane oxidations are especially attractive as silanols are a key element in the production of silicon-containing materials.2 However, conventional routes for the silane oxidation generally require the presence of strong and toxic oxidants such as permanganate and dichromate.2 Here, we demonstrate that high catalytic performances (TOF = 590000 h-1) could be achieved towards the green oxidation of silanes and H2 production under ultralow Au loadings (0.001 – 0.0002 mol % in terms of Au) employing H2O as the oxidant, 25 oC as the reaction temperature, and MnO2 nanowires decorated with ultrasmall Au NPs (having diameters of 3 nm or less) as catalysts.

Journal of Physics: Conference Series, 2017

Two novel automated methods for the determination of surface roughness and chemical distribution ... more Two novel automated methods for the determination of surface roughness and chemical distribution in individual nanoparticles are presented and applied to nanoparticles synthesised by the galvanic replacement reaction. The two methodologies apply the determination of circumferential and radial line profiles to determine surface roughness and elemental distribution respectively. The surface roughness analysis provides details on localised changes in roughness in comparison to single measures of circularity. The X-ray spectroscopic concentric ring scan outperforms conventional line scans when elemental distribution approximately possesses a spherical symmetry.

ChemCatChem, 2018

Studies on surface plasmon resonance (LSPR) mediated catalytic transformations have focused on qu... more Studies on surface plasmon resonance (LSPR) mediated catalytic transformations have focused on quantification of reaction rates and investigation on enhancement mechanisms. However, the establishment of structure‐performance relationships remains limited. For instance, the importance of nanoparticle size remains overlooked, and relatively large nanoparticles (>50 nm in size) are generally employed as catalysts. Herein, we unravel how plasmon decay pathways (absorption and scattering efficiencies) and electric field enhancements as a function of size dictate plasmonic catalytic performances. We employed Ag NPs having 12–50 nm in size as a proof‐of‐concept catalysts, and the LSPR‐mediated oxidation of p‐aminothiophenol to p,p′‐dimercaptoazobenzene as a model reaction. Our data and simulations revealed that the LSPR‐mediated activities displayed a volcano‐type variation with size, which was dependent on the balance among near field enhancements, absorption, and scattering. As this transformation is driven by the charge‐transfer of LSPR‐excited hot‐electrons to adsorbed O2 molecules, the variations in the optical absorption as a function of size represented the dominant contribution to the plasmonic catalytic activities. We believe our results shed important insights over the optimization of physical and chemical parameters in plasmonic nanoparticles in order to maximize plasmonic catalytic activities.

Journal of Materials Science, 2019

We reported herein a systematic investigation on how the nature of the support affected the catal... more We reported herein a systematic investigation on how the nature of the support affected the catalytic performances of Rh nanoparticles. The prepared catalysts were denoted as Rh/M x O y , where M corresponded to Ce, Ti, Si, Zn, and Al, and Rh was Rh 3? reduction to Rh nanoparticles on the surface of oxides. This strategy was performed in a single step using urea as a mediator and in the absence of any other stabilizer or capping agent. The Rh nanoparticles displayed relatively similar sizes, shapes, and uniform distribution over the supports, differing only in terms of the nature of the support. This strongly affected the metal-support interaction between Rh nanoparticles and the respective oxides, leading to significant differences in their catalytic performances toward the ethanol steam reforming. Here, not only the catalytic activity (in terms of ethanol conversion) was affected, but both the selectivity and stability were also influenced by the nature of the oxide support. Interestingly, the reaction paths as well as the deactivation profile were completely changed as function of the employed support. Such differences were associated with differences in the oxygen storage, oxygen mobility, and acidity/basicity of the supports. We believe that our results can contribute to the development and understanding of Rh-supported catalysts for the applications toward gas-phase transformations such as the ethanol steam reforming reaction.

Faraday discussions, Jan 29, 2018

In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understan... more In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understanding of the composition-dependent catalytic activity of these nanoparticles. AgAu nanoparticles were synthesized via the galvanic replacement method with controlled size and nanoparticle compositions. We studied extinction spectra with UV-Vis spectroscopy and simulations based on Mie theory and the boundary element method, and ultrafast spectroscopy measurements to characterize decay constants and the overall energy transfer dynamics as a function of AgAu composition. Electron-phonon coupling times for each composition were obtained from pump-power dependent pump-probe transients. These spectroscopic studies showed how nanoscale surface segregation, hollow interiors and porosity affect the surface plasmon resonance wavelength and fundamental electron-phonon coupling times. Analysis of the spectroscopic data was used to correlate electron-phonon coupling times to AgAu composition, and thu...

Journal of Chemical Education, 2017

Undergraduate-level laboratory experiments that involve the synthesis of nanomaterials with well-... more Undergraduate-level laboratory experiments that involve the synthesis of nanomaterials with well-defined/ controlled shapes are very attractive under the umbrella of nanotechnology education. Herein we describe a low-cost and facile experiment for the synthesis of Cu(OH) 2 and CuO nanowires comprising three main parts: (i) synthesis of Cu(OH) 2 nanowires by a precipitation approach followed by a calcination step that converts Cu(OH) 2 to CuO; (ii) use of Cu(OH) 2 and CuO nanowires as model systems to explore a variety of characterization techniques relevant in the context of solid-state chemistry, materials chemistry, and nanoscience; and (iii) presentation/discussion of the data. Other learning objectives include probing of chemical transformations at the nanoscale and the use of concepts borrowed from coordination chemistry to understand the formation mechanism of Cu(OH) 2 and CuO nanowires from a Cu 2+ (aq) precursor. This experiment can be performed with a relatively simple laboratory infrastructure and with instrumentation that is generally widely available. Moreover, students are able to integrate multidisciplinary concepts in a single activity and become introduced to/familiarized with a currently active research field (nanoscience) and its associated literature.

Catalysis Science & Technology, 2014

Heterogeneous catalysts based on Sm-doped ceria were employed for the first time in the liquid-ph... more Heterogeneous catalysts based on Sm-doped ceria were employed for the first time in the liquid-phase oxidation of α-bisabolol. Nanometer-sized catalysts were obtained by microwave-hydrothermal synthesis and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), Raman spectroscopy and N 2-physisorption. The influence of Sm doping, temperature and the solvent used on the catalytic behavior was investigated. Conversions up to 84% and a combined selectivity for the products up to 77% were obtained for Ce 0.9 Sm 0.15 O 1.85−δ catalysts. The reactions were highly selective for the epoxidation products (only bisabolol oxides A and B were obtained) and shown to be strongly dependent on the temperature and solvent employed. Best results were achieved for higher Sm concentrations, which indicate that changes in the textural properties due to doping produced a significantly more active catalyst.

Advanced Synthesis & Catalysis, 2018

Applications of gold and selenium chemistry are reported as novel approaches to promote lignin de... more Applications of gold and selenium chemistry are reported as novel approaches to promote lignin depolymerization into more valuable chemicals via selective oxidation reactions (alcohol oxidations and Baeyer-Villiger reactions). In this study, we proposed two different oxidative methodologies using Au/SiO2 and phenylseleninic acid resin (PAR) as stable and reusable catalysts to promote selective transformations of the β-O-4 linkage of lignin model compounds. After evaluating the catalytic systems under batch conditions, they were both applied in a packed-bed reactor for continuous flow operations. By using Au/SiO2 as a catalyst under flow conditions, ketones were efficiently obtained (up to 86% conversion) from the oxidation of alcohols with a residence time (tR) of 30 min. In the case of Baeyer-Villiger oxidations catalyzed by phenylseleninic acid resin, the corresponding esters were obtained in up to 91% conversion (tR = 30 min). Both systems efficiently catalyzed the conversion of the lignin model compounds.

Particle & Particle Systems Characterization, May 1, 2018

ECS Transactions, 2019

Solid oxide fuel cells are fabricated by two-step sintering at low temperature by controlling the... more Solid oxide fuel cells are fabricated by two-step sintering at low temperature by controlling the morphology of the gadolinium-doped cerium oxide (GDC) electrolyte powders. The GDC electrolyte was synthesized by a hydrothermal route to obtain highly reactive nanorods that can fully densify at temperatures around 1150 °C. The developed system consists of the GDC electrolyte support, lanthanum strontium cobalt ferrite (LSCF) cathode and Ni/GDC anode. The electrolyte support was prepared by uniaxial die pressing and sintered at 1150 °C, and fuel cells were obtained by co-sintering electrode layers at the same temperature. The performance of the cell was evaluated in hydrogen at intermediate temperatures (IT). The experimental results indicate that high-performance IT-SOFC can be obtained at low sintering temperatures by controlling the morphology of electrolyte powder.

Chemistry – A European Journal, 2019

CrystEngComm, 2019

Mass diffusion controls material structuring from the atomic to the macro-scale defining properti... more Mass diffusion controls material structuring from the atomic to the macro-scale defining properties and functionalities.

Tetrahedron Letters, 2017

We report herein the high yield synthesis of Cu 2 O spheres displaying well-defined shapes and mo... more We report herein the high yield synthesis of Cu 2 O spheres displaying well-defined shapes and monodisperse sizes that could be employed as the source of highly catalytic active Cu(I) species towards click reactions between several of alkynes and azides to produce a variety of 1,2,3-triazoles under ligand-free and ambient conditions (in an open reactor). The utilization of Cu 2 O spheres enabled superior performance as compared to a conventional protocol in which CuSO 4 is employed in combination with sodium ascorbate as the catalyst system. In addition, the compounds were obtained in synthetically useful yields, and seven of them have not been previously reported. We believe the results reported herein shed new insights into the optimization of activity and versatility of click reactions towards the synthesis of target molecules in environmentally friendly conditions.

Fuel, 2019

We reported herein the synthesis in high yields (> 97%) of Ce 0.9 Sm 0.1 O 2-δ nanowires displayi... more We reported herein the synthesis in high yields (> 97%) of Ce 0.9 Sm 0.1 O 2-δ nanowires displaying well-defined shape, size, and composition by a simple, fast, and low-cost two-step hydrothermal method. The Ce 0.9 Sm 0.1 O 2-δ nanowires synthesis was followed by the wet impregnation of Ni without the utilization of any stabilizing agent. The Ni/Ce 0.9 Sm 0.1 O 2-δ nanowires showed higher surface area, high concentration of oxygen vacancies at surface, and finely dispersed Ni particles with significantly higher metallic surface area as compared with catalysts prepared from commercial materials with similar compositions. Such unique and improved properties are reflected on the catalytic performance of the Ni/Ce 0.9 Sm 0.1 O 2-δ nanowires towards ethanol steam reforming. The nanowires exhibited high yields for hydrogen production (∼60% of selectivity) and an exceptional stability with no loss of activity after 192 h of reaction at 550°C. The reported results provide insights and can inspire highyield production of nanostructured catalysts displaying controlled and superior properties that enable practical applications in heterogeneous catalysis.

Materials Chemistry and Physics, 2021

ABSTRACT A proteic sol-gel route was used in the production of NiMoO4 catalysts, which used edibl... more ABSTRACT A proteic sol-gel route was used in the production of NiMoO4 catalysts, which used edible gelatin as a precursor. The triple helix structure of a protein in contact with identical structures acquires an unfolded form, which favors the interaction of the reactive groups of the gelatin (NH3+ and COO-) with the metallic ions (MoO42- and Ni2+). The synthesized catalysts were thoroughly characterized using techniques such as X-ray diffraction, thermogravimetric and differential thermal analysis, Raman scattering, scanning and transmission electron microscopies, UV-Vis spectroscopy, and colorimetry. The results showed that it is possible to prepare the phase-pure α-NiMoO4 polymorph only at temperatures above 700 °C, while a mixture of the polymorphs α and β were obtained at lower temperatures. The synthesized materials calcined at 300, 500, and 700 °C have their catalytic potentials tested in the ethanol steam reforming reaction aiming the production of hydrogen and presented a good performance. The results indicated that among tested materials, the sample calcined at 700 °C exhibited the highest stability, activity, and best selectivity relative to the product of interest.

Nanoscale, Jan 10, 2018

Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or... more Plasmonic catalysis takes advantage of the surface plasmon resonance (SPR) excitation to drive or accelerate chemical transformations. In addition to the plasmonic component, the control over metal-support interactions in these catalysts is expected to strongly influence the performances. For example, CeO2 has been widely employed towards oxidation reactions due to its oxygen mobility and storage properties, which allow for the formation of Ce3+ sites and adsorbed oxygen species from metal-support interactions. It is anticipated that these species may be activated by the SPR excitation and contribute to the catalytic activity of the material. Thus, a clear understanding of the role played by the SPR-mediated activation of surface oxide species at the metal-support interface is needed in order to take advantage of this phenomenon. Herein, we describe and quantify the contribution from active surface oxide species at the metal-support interface (relative to O2 from air) to the activit...