Origins of the Rio Capim kaolinites (northern Brazil) revealed by δ18O and δD analyses

Deuterium (δD) and oxygen (δ¹⁸O) isotope data from the Rio Capim kaolin, northern Brazil, were combined with optical studies in order to better understand the genesis and evolution of the kaolinites. The results show that δ¹⁸O values from a lower soft kaolin unit range from 6.0‰ to 19.2‰ for Ka (size ranging from 1 to 3 μm) and Kb (size ranging from 10 to 30 μm) kaolinites, and from 15.4‰ to 24.9‰ for Kc (size < 200 nm) kaolinites. The δD values range from − 63.1‰ to 79.5‰ for the Ka + Kb kaolinites, and from − 68.8‰ to − 244.35‰ for the Kc kaolinites. An upper semi flint kaolin unit, dominated by Kc kaolinites, displays δ¹⁸O and δD values ranging from 15.1‰ to 21.8‰, and − 71.3‰ to − 87.4‰, respectively. Based on these data, and on the δ¹⁸O and δD values obtained for the surface meteoric water and groundwater, it can be concluded that the kaolinites are not in equilibrium with the modern weathering environment, but they reflect isotopic compositions of the formation time, probably due to the interaction with fossil groundwater. However, mineralogical contaminations derived from replacements of framework grains also had great influence in the isotopic composition of these kaolinites. In addition, the isotope values of the Kc kaolinites from the semi-flint kaolin unit is variable, which is due to the presence of Kc kaolinites of different origins, including kaolinites derived from the underlying soft kaolin unit, kaolinites formed during different phases of paleoweathering, as well as later phases of coarse-grained kaolinites formed along fractures. Due to these complexities, binary diagrams contrasting δ¹⁸O and δD values, worldwide applied for distinguishing supergenic from hypogenic kaolinites, as well as those formed under weathering conditions, can not be applied to interpret the origin of the kaolinites in the Rio Capim Kaolin.     

High temperature SrCe0.9Eu0.1O3−δ proton conducting membrane reactor for H2 production using the water–gas shift reaction

The water–gas shift (WGS) reaction is used to shift the CO/H₂ ratio prior to Fischer–Tropsch synthesis and/or to increase H₂ yield. A WGS membrane reactor was developed using a mixed protonic–electronic conducting SrCe_0.9Eu_0.1O_3−δ membrane coated on a Ni–SrCeO_3−δ support. The membrane reactor overcomes the thermodynamic equilibrium limitations. A 46% increase in CO conversion and total H₂ yield was achieved at 900 °C under 3% CO and 6% H₂O, resulting in a 92% single pass H₂ production yield and 32% single pass yield of pure permeated H₂.     

Acceleration effect of sericin on shear-induced β-transition of silk fibroin

Although silk sericin (SS) occupies 25% of silk protein, its importance has often been overlooked in the natural silk spinning process and in the formation of the crystalline structure of silk fibroin (SF). In this study, we elucidated the role of SS in the crystallization process of SF under shear using SF/SS blend solutions. In order to apply shear stress to the blend solution, a rotating glass rod was inserted into a glass tube filled with the solution and the shear rate was determined to be in the range of 598–724 s⁻¹. After shearing, SF aggregates were formed and the amount of the aggregates increased with shearing time. Additionally, it was observed that the aggregate formation and β-sheet transition of SF were enhanced when a proper amount of SS was in the blend solution. Consequently, the SS considerably contributes to the structural transition of SF under shear. The SS can improve the shear-induced β-sheet transition and crystallization of SF.     

Isomerization of α-pinene over dealuminated ferrierite-type zeolites

Isomerization of α-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using ²⁹Si, ²⁷Al, ¹H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity of the zeolite particles, the treatments removed up to 53% of the tetrahedrally coordinated aluminum atoms from the FER framework. According to ²⁹Si MAS NMR studies, the framework aluminum atoms located at the 10-membered rings in the main channels of FER (T_B sites) were depleted preferentially from their positions. Even relatively mild dealumination of FER led to an active catalyst containing both Brønsted and Lewis centers, yielding up to 97% conversion of α-pinene at 363 K, in contrast to the 72% observed for the parent hydrogen form. Such catalytic behavior was discussed in terms of the conversion of a reactant inside micropores of the zeolite catalyst, on Brønsted acid centers with enhanced strength located probably in the vicinity of Lewis sites. The selectivity toward camphene and limonene changed smoothly with the dealumination level; thus, a higher selectivity toward limonene was observed at the expense of camphene formation with increasing the n_Si/n_Al ratio of the catalysts. The selectivity toward camphene and limonene was close to 85% for all of the materials studied. The initial rates of α-pinene transformations over FER-type materials exceeded those observed for other catalytic systems, heteropoly acid/SiO₂ and H₂SO₄/ZrO₂. This study demonstrates the successful application of a medium-pore zeolite for the catalytic transformation of α-pinene in liquid phase.     

Improving the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes by a surface-coating layer of GdBaCo2O5+δ

A GdBaCo₂O_5+δ layer was coated on the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes to enhance their oxygen permeability by employing the fast oxygen adsorption/desorption surface-exchange properties of the GdBaCo₂O_5+δ material. The oxygen flux of the coated and uncoated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes was measured in the temperature range of 600–850 °C. The results reveal that the oxygen-permeation flux of the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes coated by a GdBaCo₂O_5+δ layer shows significant enhancement. The GdBaCo₂O_5+δ layer coated on the oxygen desorption side (He side) has much effect than that coated on the oxygen adsorption side (air side). At 850 °C, the oxygen flux with a single coating layer on the air side can rise 16%, while a single coating on the helium side will result into a rise of 23%.     

Highly efficient complete oxidation of dilute benzene over ultrafine Cu0.1Ce0.5Zr0.4O2−δ catalyst in a fluidized bed reactor

Ultrafine Cu_0.1Ce_0.5Zr_0.4O_2−δ catalyst operated in a fluidized bed reactor was found to be very effective for complete oxidation of dilute benzene in air. The complete conversion of benzene could be achieved at reaction temperature as low as 220 °C. The mechanism of benzene oxidation over the Cu_0.1Ce_0.5Zr_0.4O_2−δ catalyst was investigated by conducting pulse reaction of pure benzene in the absence of O₂ over the catalyst and the results indicated the involvement of lattice oxygen from the catalyst in benzene oxidation.     

Polymer-polymer interaction parameters in the ternary system polystyrene/poly(α-methyl styrene)/n-butyl chloride

The polymer-polymer interaction parameter χ′12, for the polystyrene/poly(α-methyl styrene)/n-butyl chloride ternary system, has been determined from activity coefficients of the solution measured using piezoelectric vapour sorption methods in the temperature range 30°–60°C. (These measurements where carried out in the concentration range 0.06 < ψ₀ < 0.26, where ψ is the segment fraction of the solvent). The values of χ¹⁰₁₂ extrapolated to zero solvent concentration over the range 30°–60°C, are large and negative (−0.2 to −0.9) χ¹₁₂ was found to increase with ψ₀. The negative values of χ¹₁₂ in this work are in agreement with the T_g in the polystyrene

Full-size image (1K)

M_w = 9.09 × 10⁴) blends on the point of blend compatibility. The polymer-polymer interaction parameters obtained in this work are discussed by taking into account the high susceptibility of polymers in the glassy state to solution of organic solvents.     

Effects of preparation methods on the oxygen nonstoichiometry, B-site cation valences and catalytic efficiency of perovskite La0.6Sr0.4Co0.2Fe0.8O3−δ

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) powders were synthesized respectively by an EDTA (ethylenediaminetetraacetic acid)–Citrate sol–gel process and a low-temperature auto-combustion process. The samples were characterized by XRD, SEM, BET, TGA and instant temperature analysis. The iodometric titration was used to determine the average valence of Co and Fe ions and the oxygen nonstoichiometry of the prepare powders. The catalytic properties of the synthesized powders were investigated by the hydrogen peroxide catalytic decomposition. Pure-perovskite structure was formed by both synthesis methods. The oxygen nonstoichiometry of the samples prepared by the auto-combustion process is larger than that by the sol–gel process. The catalytic activities of the powders from two synthesis processes also differed largely due to the different oxygen nonstoichiometry, surface area and crystalline sizes.     

Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3−xTixO4 (0 ≤ x ≤ 0.78) at neutral pH values

In this work, a series of Fe_3−xTi_xO₄ (0 ≤ x ≤ 0.78) was synthesized using a new soft chemical method. The synthetic Fe_3−xTi_xO₄ were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures.Then, decolorization of methylene blue (MB) by Fe_3−xTi_xO₄ in the presence of H₂O₂ at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC), ¹³C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe_3−xTi_xO₄ in the presence of H₂O₂ was promoted remarkably with the increase of Ti content in Fe_3−xTi_xO₄ due to the enhancement of both adsorption and degradation of MB on Fe_3−xTi_xO₄.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Intrinsic kinetics of Fischer–Tropsch reactions over an industrial Co–Ru/γ-Al2O3 catalyst in slurry phase reactor

The rate of Fischer–Tropsch synthesis over an industrial well-characterized Co–Ru/γ-Al₂O₃ catalyst was studied in a laboratory well mixed, continuous flow, slurry reactor under the conditions relevant to industrial operations as follows: temperature of 200–240 °C, pressure of 20–35 bar, H₂/CO feed ratio of 1.0–2.5, gas hourly space velocity of 500–1500 N cm³ g_cat^− 1 h^− 1 and conversions of 10–84% of carbon monoxide and 13–89% of hydrogen. The ranges of partial pressures of CO and H₂ have been chosen as 5–15 and 10–25 bar respectively. Five kinetic models are considered: one empirical power law model and four variations of the Langmuir–Hinshelwood–Hougen–Watson representation. All models considered incorporate a strong inhibition due to CO adsorption. The data of this study are fitted fairly well by a simple LHHW form − R_H2 + CO = ap_H2^0.988p_CO^0.508 / (1 + bp_CO^0.508)² in comparison to fits of the same data by several other representative LHHW rate forms proposed in other works. The apparent activation energy was 94–103 kJ/mol. Kinetic parameters are determined using the genetic algorithm approach (GA), followed by the Levenberg–Marquardt (LM) method to make refined optimization, and are validated by means of statistical analysis. Also, the performance of the catalyst for Fischer–Tropsch synthesis and the hydrocarbon product distributions were investigated under different reaction conditions.     

A new class of corrosion inhibitors for waterborne coatings: 4-methyl-γ-oxo-benzene-butanoic acid complexes

Amine and transition metal based complexes with 4-methyl-γ-oxo-benzene-butanoic acid represent a new class of corrosion inhibitors specifically designed for long-term corrosion protection in waterborne coatings. Today, corrosion protection in waterborne technology is typically achieved using traditional anticorrosive pigments initially developed for use in solventborne coatings. Regulations concerning heavy metals and limitations regarding the compatibility and performance of such materials in waterborne coatings have created a need for novel approaches. Mechanistic aspects are discussed for the 4-methyl-γ-oxo-benzene-butanoic complexes based on electrochemical solution experiments (electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV)) and investigations performed on coated substrates. Exposure results underline the high efficiency of such complexes for both long-term corrosion protection and weld seam rust control in waterborne coatings.     

Performance of Pd catalysts supported on nanocrystalline α-Al2O3 and Ni-modified α-Al2O3 in selective hydrogenation of acetylene

Nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ have been prepared by sol–gel and solvothermal methods and employed as supports for Pd catalysts. Regardless of the preparation method used, NiAl₂O₄ spinel was formed on the Ni-modified α-Al₂O₃ after calcination at 1150 °C. However, an addition of NiO peaks was also observed by X-ray diffraction for the solvothermal-made Ni-modified α-Al₂O₃ powder. Catalytic performances of the Pd catalysts supported on these nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ in selective hydrogenation of acetylene were found to be superior to those of the commercial α-Al₂O₃ supported one. Ethylene selectivities were improved in the order: Pd/Ni-modified α-Al₂O₃–sol–gel > Pd/Ni-modified α-Al₂O₃-solvothermal ≈ Pd/α-Al₂O₃–sol–gel > Pd/α-Al₂O₃-solvothermal  Pd/α-Al₂O₃-commerical. As revealed by NH₃ temperature program desorption studies, incorporation of Ni atoms in α-Al₂O₃ resulted in a significant decrease of acid sites on the alumina supports. Moreover, XPS revealed a shift of Pd 3d binding energy for Pd catalyst supported on Ni-modified α-Al₂O₃–sol–gel where only NiAl₂O₄ was formed, suggesting that the electronic properties of Pd may be modified.     

High-performance Li4Ti5−xVxO12 (0 ≤ x ≤ 0.3) as an anode material for secondary lithium-ion battery

Powders of spinel Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were successfully synthesized by solid-state method. The structure and properties of Li₄Ti_5−xV_xO₁₂ (0 ≤ x ≤ 0.3) were examined by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electronic microscope (SEM), galvanostatic charge–discharge test and cyclic voltammetry (CV). XRD shows that the V⁵⁺ can partially replace Ti⁴⁺ and Li⁺ in the spinel and the doping V⁵⁺ ion does almost not affect the lattice parameter of Li₄Ti₅O₁₂. Raman spectra indicate that the Raman bands corresponding to the Li–O and Ti–O vibrations have a blue shift due to the doping vanadium ions, respectively. SEM exhibits that Li₄Ti_5−xV_xO₁₂ (0.05 ≤ x ≤ 0.25) samples have a relative uniform morphology with narrow size distribution. Charge–discharge test reveals that Li₄Ti_4.95V_0.05O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 1.0 and 2.0 V; Li₄Ti_4.9V_0.1O₁₂ has the highest initial discharge capacity and cycling performance among all samples cycled between 0.0 and 2.0 V or between 0.5 and 2.0 V. This excellent cycling capability is mainly due to the doping vanadium. CV reveals that electrolyte starts to decompose irreversibly below 1.0 V, and SEI film of Li₄Ti₅O₁₂ was formed at 0.7 V in the first discharge process; the Li₄Ti_4.9V_0.1O₁₂ sample has a good reversibility and its structure is very advantageous for the transportation of lithium-ions.     

β-MnO2 nanowires: A novel ozonation catalyst for water treatment

Using Mn(NO₃)₂ and ozone as raw materials, β-MnO₂ nanowires with diameters of about 6–12 nm, lengths of 2–5 μm and surface area of 73.54 m² g⁻¹ were synthesized by a simple hydrothermal process. The influences of synthesis conditions such as hydrothermal temperature, reaction time and ozone were investigated, and the growth process of β-MnO₂ nanowires was discussed. The catalytic properties of β-MnO₂ nanowires for the degradation of phenol were evaluated. β-MnO₂ nanowires revealed good separability and remarkable catalysis for the degradation of phenol.     

Synthesis of onion-like mesoporous silica from sodium silicate in the presence of α,ω-diamine surfactant

Mesoporous silicas with vesicular and onion-like morphologies were assembled through hydrogen-bonding pathway from sodium silicate as silica source and electrically neutral α,ω-diamine, Jeffamine D2000 surfactant (H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂) as template in aqueous media at different synthesis temperatures (25, 60 and 100 °C). Assembling the material at 100 °C afforded onion-like core shell mesoporous silica, while at relatively lower temperature, e.g. 25 and 60 °C, multilamellar vesicles were obtained. Mesoporous silica with onion-like morphology was also obtained by a two-step synthesis involving an aging period of 20 h at room temperature followed by a hydrothermal stage (1–12 h) at 100 °C. The heavily cross-linked (Q⁴/Q³ ratio of 4.43) onion-like mesophase silica exhibited high hydrothermal stability. The BET surface area, pore volume and KJS (Kruk-Jaroniec-Sayari) pore diameter of the onion-like mesoporous silica were found to be 464 m² g⁻¹, 1.16 m³ g⁻¹ and 7.2 nm, respectively.     

Electrochemical promotion of a platinum catalyst supported on the high-temperature proton conductor La0.99Sr0.01NbO4−δ

The recently discovered, high-temperature proton conductor, La_0.99Sr_0.01NbO_4−δ, was used as a support for the electrochemical promotion of a platinum catalyst. Ethylene oxidation was used as a probe reaction in the temperature range 350–450 °C. Moderate non-Faradaic rate modification, attributable to a protonic promoting species, occurred under negative polarisation; some permanent promotion was also observed. In oxidative atmospheres, both the p_O2 of the reaction mixture and the temperature influenced the type and magnitude of the observed rate modification. Rate-enhancement values of up to ρ = 1.4 and Faradaic-efficiency values approaching Λ = −100 were obtained. Promotion was observed under positive polarisation and relatively dry, oxygen-rich atmospheres suggesting that some oxygen ion conductivity may occur under these conditions. Impedance spectroscopy performed in atmospheres of 4 kPa O₂/N₂ and of 5 kPa H₂/N₂ under dry and slightly humidified (0.3 kPa H₂O) conditions indicated that the electrical resistivity is heavily dominated by the grain-boundary response in the temperature range of the EPOC studies; much lower grain-boundary impedances in the wetter conditions are likely to be attributable to proton transport.     

High activity, templated mesoporous SO4/ZrO2/HMS catalysts with controlled acid site density for α-pinene isomerisation

Highly active mesoporous SO₄/ZrO₂/HMS (hexagonal mesoroporous silica) solid acid catalysts with tuneable sulphated zirconia (SZ) content have been prepared for the liquid phase isomerisation of α-pinene. The mesoporous HMS framework is preserved during the grafting process as evidenced by the X-ray diffraction (XRD) and porosimetry with all SO₄/ZrO₂/HMS materials possessing average pore-diameters 20 Å. XRD confirms the presence of a stabilized tetragonal phase of nanoparticulate ZrO₂, with no evidence for zirconia phase separation or the formation of discrete crystallites, consistent with a uniform and highly dispersed SZ coating. The activity towards α-pinene isomerisation scales linearly with Zr loading, while the specific activities are an order of magnitude greater than attainable by conventional methodologies (1 versus 0.08 mol h⁻¹ g Zr⁻¹).     

La(1−x)SrxCo1−yFeyO3 perovskites prepared by sol–gel method: Characterization and relationships with catalytic properties for total oxidation of toluene

La_(1−x)Sr_xCo_(1−y)Fe_yO₃ samples have been prepared by sol–gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co₃O₄ that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 °C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La³⁺ by Sr²⁺ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La_0.7Sr_0.3Co_0.8Fe_0.2O₃. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mössbauer spectroscopy. Cobalt oxidation states and the amount of O⁻ electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La³⁺ by Sr²⁺. The strong lowering of the temperature at conversion 20% for the La_0.7Sr_0.3Co_(1−y)Fe_yO₃ samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O⁻ electrophilic species for the La_0.7Sr_0.3Co_(1−y)Fe_yO₃ samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O⁻ species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn–Teller effect and Mössbauer spectroscopy evidenced the presence of Fe⁴⁺ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La_0.7Sr_0.3Co_0.8Fe_0.2O₃ sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co₃O₄ particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co₃O₄.     

Substantially enhancing enzymatic regioselective acylation of 1-β-d-arabinofuranosylcytosine with vinyl caprylate by using a co-solvent mixture of hexane and pyridine

Novozym 435-catalyzed regioselective acylation of 1-β-d-arabinofuranosylcytosine (ara-C) with vinyl caprylate for the preparation of its 5′-O-acyl derivative has been performed in six co-solvent mixtures and three pure polar solvents for the first time. Novozym 435 displayed low activity towards 1-β-d-arabinofuranosylcytosine in pure polar solvents, although those solvents can dissolve the nucleosides well. When a hexane–pyridine co-solvent system was adopted, both the initial rate and the substrate conversion were enhanced markedly. The most suitable co-solvent, initial water activity, reaction temperature and the molar ratio of vinyl caprylate to ara-C were hexane/pyridine (28/72, v/v), 0.03, 40 °C and 15, respectively. Under these conditions, the initial rate, the substrate conversion and the regioselectivity were as high as 99.0 mmol h⁻¹, 98% and >99%, respectively. The product of the Novozym 435-catalyzed reaction was characterized by ¹³C NMR and confirmed to be 5′-O-octanoyl 1-β-d-arabinofuranosylcytosine.