J.A. Montoya

Catalytic decomposition of methane over Ni-Al2O3 coprecipitated catalysts: Reaction and regeneration studies

Abstract The catalytic decomposition of methane over nickel catalysts is a potential alternative route to steam reforming or partial oxidation for the production of hydrogen from natural gas and other feedstocks. In the present paper, we report the results of characterization and catalytic behaviour of a Ni(30%)/Al2O3 catalyst during the catalytic decomposition of methane. The influence of the operating and reduction temperatures and feed composition on the methane conversion, hydrogen production and coking rate has been studied. The effects of the regeneration cycles with oxygen on activity and carbon formation are also investigated. It has been shown that H2 inhibits both the carbon filament formation and the encapsulation of metallic particles by coke. An increase in the reaction temperature increases both the deactivation rate and the growth rate of filaments. However, at high reduction temperatures, there is a decrease in the number of filaments formed due to sintering of the Ni particles. A kinetic model has been developed for the prediction of H2 production and of carbon, taking into account both stages of carbon formation, nucleation and filament growth.

Influence of the hydrophobic material content in the gas diffusion electrodes on the performance of a PEM fuel cell

In the present study the influence of the hydrophobic material (Teflon, polytetrafluoroethylene) content in the gas diffusion electrodes (anode and cathode) on the performance of a H 2 /O 2 proton exchange membrane fuel cell is reported. The potential-current (E-I) evaluation of the fuel cell indicated that a combination of 10 and 30 wt% of Teflon, respectively, in the cathode and anode gave the best results.

Anti-inflammatory and anti-bacterial activity, and CYTOTOXICITY of halloysite surfaces

Halloysite is a naturally-occurring nanomaterial occurring in the thousands of tons and that serves as biomaterial, with applications in the areas of biotechnology, pharmaceutical, and medical research. This study reports on the anti-inflammatory, cytotoxic, and anti-oxidant activity of halloysite Jarrahdale (collected at ∼ 45 km SE of Perth, Western Australia; JA), Dragon Mine (provided by Natural Nano Inc., Rochester, New York; NA), and Kalgoorie Archean (collected at Siberia, ∼ 85km NW of Kalgoorlie, West Australia; PA). Prior to biological testing, halloysites were characterized by 27Al and 29Si Nuclear Magnetic Resonance Spectroscopy, the anti-inflammatory activity was determined by (a) the mouse ear edema method, using 12-o-tetradecanoylphorbol-13-acetate (TPA) as anti-inflammatory agent; and (b) the myeloperoxidase enzymatic activity method (MPO). Cell viability was determined using the MTT method. Sample characterization by NMR method showed similar symmetry and atomic environments, with no evidence of distortion(s) due to shiftings in atomic ordering or electron density. The anti-inflammatory activity followed the order: PA>JA>NA, and remained invariant with time. Prolonged anti-inflammatory activity related inversely to surface area and lumen space. The low extent of infiltration at shorter reaction times confirmed a limiting number of active surface sites. EPR intensity signals followed the order: JA>NA>PA. The poor stabilization of RO species in PA suspensions was explained by tube alignment provoking occlusion, thus limiting transfer of H(+) or e(-) from-and-to the surface, and decreases in acidity associated to Al(oct). Cell viability (%) varied from one surface to the other, PA(92.3 ± 6.0), JA(84.9 ± 7.8), and NA(78.0 ± 5.6), but related directly to SBET values.

Cinnabar-Preserved Bone Structures from Primary Osteogenesis and Fungal Signatures in Ancient Human Remains

The Red Queen remains (700 A.C.) found at Palenque, México, are examples of cinnabar (HgS) application to royal remains during pre-Hispanic times. The Red Queen remains are those of a ca. 30–35-yr-old female and present a striking similarity to the remains of another Mayan woman found at Copan, Honduras. Thus, covering the remains of royal women with HgS may have been a common practice in the Mayan civilization. High resolution microdiffraction and microscopic analysis of the Red Queen remains showed the presence of nanotubular organic minerals comparable in composition and molecular dimensions to collagen fibrils, and in spatial ordering to collagen fiber networks. Fungal structures are rare in the geological record because of poor preservation potential. Micrographs revealed the preservation of fungal signatures, with morphology comparable to parasitic fungal-coral matrix associations, consistent with the idea that fungal remains can be preserved in environments which contain high Hg concentrations. The well-preserved signatures of fungus-animal interactions and primary osteogenesis in the Red Queen remains are attributed to the long-term antibacterial activity of HgS and the association of sulfur components with nanotubular structures.

Selective Modification of Pt Active Sites on Pt–Au/C Catalysts Prepared by Surface Redox Reactions

This study focused on the selective deposition of Au0 onto (111), (100) faces and (111)/(100) edges of cuboctahedral Pt particles present on the Pt/C(graphite) model system. The Pt–Au/C catalysts were prepared by novel surface redox methods involving the direct reduction (DR) of AuCl4− species onto the Pt particles or reducing these species on the Pt–H interface, i.e., the refilling (RE) method. The presence of Au on the Pt particles was verified by means of high-resolution energy dispersive spectroscopy (EDS), and, after treatment at 300 °C in H2, the formation of crystalline Au0 aggregates was verified by X-ray wide-angle diffraction; further treatments at 500 °C in H2 led to a true Pt–Au solid solution. The Monte Carlo simulation methods indicated the selective deposition of Au0 onto the (111)/(100) edges of the Pt cuboctahedral particles when the relative Au concentration varied from 10 to 50 wt% Au. The catalytic conversion of n-heptane on the Pt–Au/C (DR and RE solids) catalysts presented an oscillatory behavior with respect to Pt/C, indicating modification of the active Pt ensembles, driven by the energy released during the exothermic n-C7 dehydrogenation and cracking reactions, which should enhance the Au0 mobility at the Pt particle surface level.

Biological dissolution and activity of the Allende meteorite

This paper reports on the effect of the Allende meteorite on the integrity of biological material and addresses the question whether it can induce cell damage via oxidative stress and cell mortality. The reaction mechanisms addressed herein are studied using electron-paramagnetic resonance spectroscopy (EPR), high-resolution transmission electron microscopy, scanning electron microscopy and energy dispersive spectroscopy, high-resolution X-ray diffraction, and the assays for thiobarbituric acid reactive substances (TBARS) and cell viability using 3-(4,5)-dimethylthiazol-2-yel-2,5-diphenyltetrazolium bromide (MTT bromide). As determined by the TBARS assay, Allende specimens induced cell damage via oxidative stress. The contents of TBARS in suspensions containing 1000 ppm of Allende and Fe 1– x S were 6.8 ± 0.7 and 5.8 ± 0.6 nmol/mg protein, respectively. EPR experiments conducted on reaction mixtures containing Allende, 5,5-dimethyl-1-pyrroline- N -oxide (DMPO), and H 2 O 2 showed a quartet signal, a 1:2:2:1 intensity, and hyperfine coupling constants corresponding to a N = 1.49 mT and a H = 1.49 mT, a signature of the DMPO-OH adduct. The intensity of the signal depended on the concentration of the solids in suspension, while the formation of DMPO-OH was limited by H 2 O 2 . Experiments were conducted to test for the production of the DMPO-OH adduct from ferric ions, and the plausible generation of HO • . The role of ethanol (CH 3 CH 2 OH) as scavenger of HO • in Allende-DMPO suspensions was addressed. Results showed a six-line spectra, with hyperfine coupling constants a N = 15.8 G, a H = 22.6 G, and g = 2.0059, consistent with the formation of the DMPO-CH(OH)-CH 3 adduct, but not DMPO-OCH 2 CH 3 . We explain these findings as the result of formation of HO • onto (or in proximity to) the mineral surface, with CH 3 CH 2 OH competing with DMPO for HO ∞ , and ferric iron playing a lesser role in DMPO transformation. Our findings are congruent with reported radical-scavenging experiments for pyrite under anoxic conditions, concluding the formation of HO ∞ at surface defect sites. Experiments conducted in Allende–desferrioxamine B(DFO-B) suspensions showed the inhibition of the formation of HO • , by means of decreases in the DMPO-OH adduct signal, accounted for by the reaction between Fe(II) and HO • to form Fe(III) and competing reaction mechanisms at the structural Fe centers, confirming that the production of HO ∞ radicals is associated with iron centers and contributes to mineral dissolution. Small-sized magnetite domains present were recognized as catalytic sites for the production of HO ∞ radicals. The γ-Fe 3 O 4 domains present in the Allende matrix exhibited a submicron range, an elongated-hexagonal habit, and a high degree of crystallinity, supporting the presence of biogenic γ-Fe 3 O 4 . Cell viability was found to be susceptible to the distribution and atomic environment of structural Fe.

Analysis of Polymorphic Nanocrystals of TiO2 by X-Ray Rietveld Refinement and High-Resolution Transmission Electron Microscopy: Acetaldehyde Decomposition

In this work, TiO2 nanocrystals were synthesized by the sol-gel method. These materials were annealed at 200 and 500∘C; and characterized by the XRD-Rietveld refinement; and by BET and TEM. As for the low-temperature-treated sample (200∘C), nanocrystals with small crystallite sizes (7 nm) and high abundance of anatase, coexisting with the brookite phase, were obtained. Meanwhile, the sample annealed at 500∘C showed an increased crystallite size (22 nm) and an important polymorphic increment. The sample annealed at 200∘C showed a high activity in the photocatalytic decomposition of acetaldehyde.

Role of Nanocrystalline Titania Phases in the Photocatalytic Oxidation of NO at Room Temperature

Nanocrystalline TiO2 powders were prepared by the sol-gel method and evaluated in the NO photocatalytic oxidation. Samples annealed at 200 and 500°C (TiO2-P-200, TiO2-P-500) were characterized by nitrogen adsorption, XRD-Rietveld refinements, TEM, FTIR and UV-vis spectroscopies. The photocatalytic test of the sol-gel TiO2 samples was carried out in an insulated chamber with 10 ppm of NO, using a 365-nm UV light lamp; the test results were compared with those obtained with a commercial catalyst (P25). Improved photoactivity (89 % of NO oxidized in 60 min) was obtained with the TiO2-P-200 solid which showed high surface area, small crystallite size, higher amount of OH and highly abundant brookite phase (37.2 %) coexisting with the anatase phase (62.8 %). The photo-oxidation activity of the sol-gel catalyst annealed at 500 °C (TiO2-P-500) showed changes in its textural and morphologic properties and therefore, less photoactivity. Sol-gel photocatalysts could be a good option for abating pollution in both indoor and outdoor environments at room temperature.

Phase Stabilization of Mesoporous Mn-Promoted ZrO2: Influence of the Precursor

Mesoporous zirconia-Mn oxides were prepared by surfactant-assisted precipitation using different zirconia precursors and cetyl-trimethyl-ammonium bromide (CTAB) as a synthetic template. The objective of this work was to find out the influence of the zirconia precursors over the structural and textural characteristics of Mn-doped mesoporous zirconia solids. A series of syntheses were carried out by two methods using different zirconia precursors, modifying the Zr:surfactant ratio and the hydrolysis rate of the precipitate. After calcination at 500 °C, the samples were characterized by XRD, DTA, TEM and nitrogen adsorption-desorption isotherm. The use of the zirconium nitrate leads to materials having higher surface areas and narrow pore size distributions in the range of mesoporous materials; however, the preferential formation of the zirconia in the metaestable tetragonal phase was identified as the effect of the particle size allowed by the preparation method rather than the effect of the precursor. It was also found that the Mn and surfactant addition enhances the stabilization of the tetragonal crystalline phase and porosity.