Impedance study of the ion-to-electron transduction process for carbon cloth as solid-contact material in potentiometric ion sensors

Carbon cloth was studied as solid-contact material in potentiometric ion sensors by using electrochemical impedance spectroscopy and potentiometry. The ion-to-electron transduction process was studied by electrochemical impedance spectroscopy by using a two-electrode symmetrical cell where a liquid electrolyte was sandwiched between two solid electrodes, including bare glassy carbon (GC), GC/carbon cloth and GC/poly(3,4-ethylenedioxythiophene). Impedance data for different electrode/electrolyte combinations were evaluated and compared. Solid-contact K⁺-selective electrodes were fabricated by coating the carbon cloth with a conventional plasticized PVC-based K⁺-selective membrane via drop casting. These K⁺-sensors showed proper analytical performance and acceptable long-term potential stability (potential drift ≈ 1 mV/day). Solid contact reference electrodes were fabricated in an analogous manner by coating the carbon cloth with a plasticized PVC membrane containing a moderately lipophilic salt. The results indicate that carbon cloth can be used as a solid-contact material in potentiometric ion sensors and pseudo-reference electrodes.     

Reaction Mechanisms of Lean-Burn Hydrocarbon SCR over Zeolite Catalysts

A large number of novel fatty compounds have been synthesized by catalytic C,C-bond forming addition reactions to the C,C-double bond of unsaturated fatty compounds. Radical reactions such as the solvent-free addition of α-halocarboxylic acid esters initiated by electron transfer, e.g., from copper to give fat-derived γ-lactones are described as well as Lewis acid–induced electrophilic addition reactions yielding new oleochemicals such as alkyl-substituted 4-chlorotetrahydropyrans, primary homoallylic alcohols, β-, γ-unsaturated ketocarboxylic acids and Diels–Alder addition products. New catalysts as, e.g., ligand-modified rhodium catalysts for the hydroformylation and heterogeneous boron-modified rhenium catalysts for the olefin metathesis have been developed. The addition of C-nucleophiles such as dimethylmalonate and nitromethane is possible by palladium-(0)catalyzed additions to unsaturated fatty compounds after conversion of the electron-rich to an electron-poor double bond. More than fifty literature articles are reviewed.     

Catalytic behaviour of M1, M2, and M1/M2 physical mixtures of the Mo–V–Nb–Te–oxide system in propane and propene ammoxidation

Essentially pure orthorhombic M1 and pseudo-hexagonal M2 phases were prepared using the precursor method. Consistent with literature the M1 phase was shown to be effective for propane ammoxidation to acrylonitrile while the M2 phase was essentially inert for propane activation. Both phases convert propene efficiently to acrylonitrile. Both phases show a significant selectivity dependence on the ammonia and oxygen concentrations in the feed, revealing thereby additional insights into the reaction mechanism.

Physical mixtures of the two separately prepared phases exhibited symbiosis in the ammoxidation of propane when finally divided (5 μm), thoroughly mixed and brought into intimate contact with each other. Acrylonitrile yields significantly higher than those obtained with the M1 phase alone were demonstrated with a 50 wt.% M1/50 wt.% M2 physical mixture having a corresponding surface area ratio of about 4:1. The phase cooperation effect is particularly large at high propane conversions and non-existent when the particle size of the phases is too large (e.g. >250 μm) and the inter-particle contact is poor.     

Soil nutrient maps of Sub-Saharan Africa: assessment of soil nutrient content at 250 m spatial resolution using machine learning

Spatial predictions of soil macro and micro-nutrient content across Sub-Saharan Africa at 250 m spatial resolution and for 0–30 cm depth interval are presented. Predictions were produced for 15 target nutrients: organic carbon (C) and total (organic) nitrogen (N), total phosphorus (P), and extractable—phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), sodium (Na), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), aluminum (Al) and boron (B). Model training was performed using soil samples from ca. 59,000 locations (a compilation of soil samples from the AfSIS, EthioSIS, One Acre Fund, VitalSigns and legacy soil data) and an extensive stack of remote sensing covariates in addition to landform, lithologic and land cover maps. An ensemble model was then created for each nutrient from two machine learning algorithms—random forest and gradient boosting, as implemented in R packages ranger and xgboost—and then used to generate predictions in a fully-optimized computing system. Cross-validation revealed that apart from S, P and B, significant models can be produced for most targeted nutrients (R-square between 40–85%). Further comparison with OFRA field trial database shows that soil nutrients are indeed critical for agricultural development, with Mn, Zn, Al, B and Na, appearing as the most important nutrients for predicting crop yield. A limiting factor for mapping nutrients using the existing point data in Africa appears to be (1) the high spatial clustering of sampling locations, and (2) missing more detailed parent material/geological maps. Logical steps towards improving prediction accuracies include: further collection of input (training) point samples, further harmonization of measurement methods, addition of more detailed covariates specific to Africa, and implementation of a full spatio-temporal statistical modeling framework.     

A kinetic modelling study of ethane cracking for optimal ethylene yield

Current generation steam cracking plants are considered to be mature. As a consequence it is becoming more and more important to know whether the underlying mechanistic cracking process offers still scope for further improvements. The fundamental kinetic limits to cracking yields have recently been researched in detail for different feed stocks with a new synthesis reactor model, d-RMix, incorporating a large scale mechanistic reaction scheme, SPYRO^® [M.W.M. van Goethem, S. Barendregt, J. Grievink, J.A. Moulijn, P.T.J. Verheijen “Model-based, thermo-physical optimisation for high olefin yield in steam cracking reactors”, Chemical Research and Engineering Developments 88 (2010) 1305–1319]. Mathematical optimization revealed for ethane cracking a maximum ethylene yield of about 67 wt%. with a linear-concave optimal temperature profile along the reaction coordinate with a maximum temperature between 1200 and 1300 K. Further mechanistic analysis of these results showed that the linear-concave shape not only suppresses the successive dehydrogenation and condensation reactions of ethylene, but mainly reduces the role of the ethane initiation reaction to form two methyl radicals.     

Influence of Stress and Chemical Homogeneity on Dielectric Properties of BaTi0.9Zr0.1O3

The influence of mechanical stress and chemical homogeneity on the permittivity of BaTi_0.9Zr_0.1O₃ ceramics prepared from mixed-oxide and hydrothermal powders was studied. To reduce stress, liquid-phase sintering was applied in conjunction with a low heating rate to stimulate the formation of large grains. The influence of chemical homogeneity was studied by variations in sintering temperatures and times. For both types of ceramics, the dielectric constant at the Curie temperature was influenced by both factors, but to a different extent. In the mixed oxide ceramic, chemical homogeneity played a more prominent role, while internal stress appeared to exert a larger influence in the hydrothermal ceramics. The dielectric constant at the Curie temperature could be increased by 5%–10% by an annealing treatment at 200°C, followed by slow cooling.     

Multi-level Modeling of Silica–Template Interactions During Initial Stages of Zeolite Synthesis

Zeolite synthesis is driven by structure-directing agents, such as tetrapropyl ammonium ions (TPA⁺) for Silicalite-1 and ZSM-5. However, the guiding role of these organic templates in the complex assembly to highly ordered frameworks remains unclear, limiting the prospects for advanced material synthesis. In this work, both static ab initio and dynamic classical modeling techniques are employed to provide insight into the interactions between TPA⁺ and Silicalite-1 precursors. We find that as soon as the typical straight 10-ring channel of Silicalite-1 or ZSM-5 is formed from smaller oligomers, the TPA⁺ template is partially squeezed out of the resulting cavity. Partial retention of the template in the cavity is, however, indispensable to prevent collapse of the channel and subsequent hydrolysis.

Self-Bonded Zeolite Beta/MCM-41 Composite Spheres

Self-bonded zeolite Beta/MCM-41 composite spheres were prepared using a two-step synthesis procedure. In the first step, mesoporous zeolite Beta spheres were obtained using anion exchange resin as macrotemplate. In the second step, the MCM-41 or Al-MCM-41 was grown both on sphere surfaces and in the pore structure of the pre-formed zeolite Beta spheres. Finally, the templating agents used in the synthesis of mesophase were removed by calcination leaving behind self-bonded Beta/MCM-41 composite spheres. Beta/MCM-41 composites were characterized by XRD, SEM and nitrogen adsorption measurements. Materials with controlled macroshape, composition and complex porosity were prepared by the approach.     

High accumulation of perfluorooctane sulfonate (PFOS) in marine tucuxi dolphins (Sotalia guianensis) from the Brazilian coast

Perfluorooctane sulfonate (PFOS) and other perfluoroalkyl compounds (PFCs) were measured in liver samples from 29 marine tucuxi dolphins from Rio de Janeiro state (RJ), Brazil. PFC measurement combined liquid chromatography and mass spectrometry, using a CapLC system connected to a Quadrupole-LIT mass spectrometer. PFOS was the only PFC detected and it was so in all samples. PFOS concentrations (ng x g(-1) dw) of dolphins (n=23) from the highly contaminated Guanabara Bay (in RJ) varied between 43 and 2431 as well as between 76 and 427 from areas of RJ other than the quoted bay (n=6). Concentrations of three fetuses and one neonate varied between 664 and 1590. Fetus/mother ratios were calculated in two situations (2.75 and 2.62). It seems that mother-to-calf transference plays important role for relationships between PFOS and age. When a one-year-old male calf presenting 2431 ng x g(-1) dw was excluded from the test, significant correlations were observed between PFOS concentrations and both age and total length. Despite the placental transference, PFOS concentrations were not significantly lower in females than in males. PFOS levels in marine tucuxi dolphins from Guanabara Bay are among the highest detected to date in cetaceans, and this may represent a threat to the small population concerned.