Apparent Order Research Articles

Kinetic analysis of the pyrolysis of wood/inorganic composites under non-isothermal conditions

The pyrolysis kinetics of wood/inorganic composites was measured using one or two kinds of inorganic modifiers (CaCO3, SiO2–TiO2, and Mg–Al compounds) to study the pyrolysis behavior. Thermogravimetric experiments were carried out under nitrogen conditions and operated at different heating rates, ranging from 10 to 40 K/min. Model-free methods (Starink, Flynne-Wall-Ozawa, and modified Coats-Redfern) were used to evaluate the kinetic parameters, including apparent activation energy (Ea) and reaction order. For the range of conversion fractions investigated (20%-80%), the results yielded Ea values of 114–117 kJ/mol, 151–158 kJ/mol, 174–175 kJ/mol, and 153–156 kJ/mol for the unmodified poplar wood and modified poplar wood composites with CaCO3, SiO2–TiO2, and Mg–Al inorganic compounds, respectively. The corresponding reaction order values were 0.4485–0.8677, 0.0150–0.3694, 0.2021–0.5579, and 0.4336–0.8293, respectively. Wood impregnated with inorganic substances had good chemical modification effect. In addition, the kinetic mechanism function of the wood pyrolysis reaction was also studied. Results show that the heating diffusion mechanism model better describes the entire pyrolysis process of the modified wood compared with the control wood, which could be attributed to difficulty in the heat transfer process because of the thermal barrier effect of the inorganic layer and the resistance of gaseous products during pyrolysis. The stability of the wood/inorganic composites is therefore effectively improved.

Memoriales modernos: inflexiones en la construcción de la memoria colectiva

Este artículo aborda los memoriales modernos a partir de las prácticas inapropiadas de algunos de sus visitantes. A través del registro de los modos de uso y promoción de los lugares de memoria y los consiguientes cuestionamientos y debates por parte de los estados, artistas e intelectuales, se propone repensar estos espacios de memoria reciente sus estéticas y las normas que los rigen. De lo que se trata es de desmontar el binomio respeto-falta de respeto entendiendo que las formas no son reaseguro de la comprensión de los sucesos recordados sino un requerimiento que sostienen un orden aparente. Se espera que las presentes reflexiones sean un aporte para fortalecer la memoria colectiva y el rol del arte contribuyendo a los debates sobre la transmisión del pasado y la musealización de la memoria.

Nucleophilic Substitution and Racemization of 3-Ethoxy-N-desmethyl-diazepam Enantiomers in Acidic Ethanol

pKal values of 3-ethoxy-N-desmethyldiazepam (3-EtO-NDZ) in ethanol and acetonitrile containing various concentrations of sulfuric acid,determined by spectrophotometry and spectropolarimetry, were found to be 3.4 and 0.63 respectively. Temperature dependent racemization of enantiomeric 3-EtO-NDZ in ethanol containing various acid concentrations was studied by monitoring changes of ellipticity at 365nm as a function of time on a spectropolarimeter. The racemization reactions were found to follow apparent first order kinetics. Thermodynamic parameters of the racemization reaction were: Eact = 16.7k cal/mol,and at 25℃:  ΔH≠ = 16.1 kcal/ mol, ΔS≠ = -22.0 cal/K/mol, and ΔG≠ = 22.6 kcal/mol, respectively. The racemization had an isotope effect (kH/kD) Of 1.9 at 42℃. Based on the results of this report and the results of literature reports on the preferred conformation of enantiomeric 3-substituted-1,4-benzodiazepines ,a nucleophilically solvated C3 carboniun ion intermediate resulting from either a P (plus) or a M (minus) conformation is proposed to be an intermediate. This intermediate is responsible for the stereoselective nucleophilic substitution and the subsequent racemization of 3-EtO-NDZ enantiomers in acidic ethanol.

Influence of Ultrasound on the Adsorption, Diffusion and Kinetics of Leather Dyeing Process: Mechanistic Insight

Leather is a natural porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. This paper studies the influence of power ultrasound on the adsorption and kinetics of leather dyeing process. Dyeing experiments have been carried out using ultrasound (150 W, 33 kHz) and compared with that of static control dyeing process. The data of dye uptake in leather have been analysed using Freundlich and Langmuir adsorption isotherms. Intra Particle diffusion model has been employed to calculate Intra particle diffusion rate constant and Boundary Layer effect. Diffusion coefficient (D) of dye through leather matrix has also been calculated. Kinetics of leather dyeing process has been studied through pseudo first and second order rate equation. The Freundlich constant (Kf), Langmuir parameter (Qm), Intra Particle diffusion rate constant (Kd) Apparent Diffusion coefficient (D) and Pseudo First order kinetic constant, K1 have been calculated to be 18.67 mg/g, 50 mg/g, 0.006 min-1, 1.89 * 10-6 cm2/s and 1.7 mg/g min0.5 respectively for ultrasound assisted leather dyeing as compared to that of 0.1 mg/g, 26.67 mg/g, 0.733 min-1, 0.19 * 10-6 cm2/s and 0.003 mg/g min0.5 respectively for control process. The results indicate that significant enhancement in adsorption capacity with more favorable dye adsorption as well as about 10- fold increase in Apparent Diffusion coefficient with significant reduction in boundary layer effect, improved kinetic parameters due to the use of ultrasound in leather dyeing as compared to control. Mechanisms for enhancement in Adsorption and Kinetic Parameters in leather dyeing due to the use of ultrasound have been presented and corroborate well with better dye penetration, color value and fastness properties. Therefore, the present study demonstrates that the use of ultrasound in leather dyeing helps both in adsorption of dyes as well as diffusion process through the leather matrix.

On the importance of by-products in the kinetics of n-butane oxidation to maleic anhydride

The kinetics of n-butane oxidation to maleic anhydride (MA) is investigated under industry-related conditions using an almost isothermal millistructured fixed-bed reactor. In addition to the influence of reaction conditions and feed composition, in particular, the influence of the reaction products is investigated. Besides water and MA, the main focus is on the by-products acetic and acrylic acid, which are usually neglected in the literature. In this context, it can be demonstrated that acetic and acrylic acid play an important role in the formation of CO and CO2, and therefore should be considered in the kinetics. On the other hand, direct oxidation of n-butane to CO and CO2 seems to be rather unlikely. The result is a reaction network with at least nine reactions. All of these reactions are inhibited by water and show an apparent reaction order smaller than one concerning their carbon source. Furthermore, a complex pattern of inhibitions is observed, which, in most cases, can be well explained by a redox mechanism. In summary, a large amount of data is collected that can be used for the development of improved kinetics, including the often neglected by-products acetic and acrylic acid.

Consequences of product inhibition in the quantification of kinetic parameters

While the potential for product inhibition in catalytic reactions is well known, the impact of neglected inhibition on measured kinetic parameters is often overlooked. The presence of product inhibition, most often caused by the competitive adsorption of products with reactants on catalytic active sites, is difficult to determine a priori for an arbitrary catalytic system. The significance of product inhibition relies on the concentration of the products, their adsorption thermodynamics on catalytically relevant sites, and process parameters such as temperature and pressure. When inhibition is significant, however, apparent activation energies and reaction orders vary from the differential-reactor apparent activation energy by a factor of 1/(1 − δ), where δ is the total inhibition order (e.g., the factor (1 − δ) = 1.6 for a system with product inhibition of −0.6 order). This is illustrated here with the kinetics of NO oxidation over Cu ion clusters (CuxOy) in Cu-SSZ-13, for which the product NO2 inhibits the forward reaction. Furthermore, in the presence of inhibition, when only reactants are fed to a flow reactor or placed in a batch reactor, there is often no practical conversion that is low enough to guarantee differential behavior. Inclusion of products in the feed solves this problem, allowing accurate determination of kinetic parameters such as apparent reaction orders and activation energies. We also demonstrate that evaluation of the necessity of co-feeding products to assure measurement of differential-reactor data in a given catalytic system is straightforward from a plot of the log of the rate (or conversion) versus the log of the space time in a flow reactor or elapsed time in a batch reactor. We encourage inclusion of this test in all kinetic analyses that are reasonably approximated by power law rate expressions.

Blood Flow in the Pancreatic Islet: Not so Isolated Anymore.

The pancreatic islet is a highly vascularized endocrine mini-organ that depends on blood supply to function efficiently. As blood flows through islet capillaries reaching different endocrine cell types, it significantly impacts nutrient sensing, paracrine communication, and the final hormonal output. Thus, any change in blood flow, either induced physiologically (e.g., nervous input) or as a result of pathological changes (e.g., fibrosis), could affect islet function. It is not a stretch to state that the way the islet vasculature is arranged anatomically and regulated functionally must have consequences for glucose homeostasis. Despite its potential impact for islet function, interest in the islet vasculature has been sporadic and is certainly not equal to that professed to the cells it serves. Still, there has been a substantive research effort in this arena. From beautiful scanning electron images of corrosion casts (1) to creative physiological experiments using perfused pancreases (2) and microbeads (3), investigators have employed various approaches to study the microcirculation of the islet. The results of these studies provided structural and functional insight but also raised questions. To settle a debate that had started in the mid-1960s, a group of prominent islet biologists decided to meet in 1996 to review existing notions about islet blood flow and “agreed to disagree” that there were three models (4). In model 1, non–β-cells are perfused before β-cells, allowing other endocrine cells to influence β-cells located downstream. In model 2, β-cells are perfused before the other endocrine cells and thus dominate islet function. In model 3, there is no apparent order of perfusion, but blood …

Oxygen pressure acid leaching of artificial sphalerite catalyzed by Fe3+/Fe2+ self-precipitation

The mechanism of oxygen pressure acid leaching of sphalerite catalyzed by Fe3+/Fe2+ self-precipitation was investigated in this study. Artificial sphalerite was fabricated with varying amounts of iron content via the sintering of ZnS and FeS and used for the pressure acid leaching experiment. The variations in the potential of the pressure leaching system were investigated by using a self-designed potential autoclave. The results showed that compared to the non-iron sphalerite, there was a violent redox reaction between the 25.70% Fe-artificial sphalerite and dissolved oxygen during the process of pressure leaching; and the catalytic mechanism was attributed to the redox couple Fe3+/Fe2+, where Fe3+oxidizes the H2S gas film and the reduced Fe2+ state is subsequently oxidized by the dissolved oxygen. Furthermore, the effect of temperature, H2SO4 concentration, and oxygen partial pressure on the artificial sphalerite with different iron contents was studied. The sphalerite samples with iron content were observed to dissolve more easily in sulfuric acid compared to the non-iron samples. Moreover, the activation energy of artificial sphalerite was observed to be lower in the sample with 25.70% iron content (22.26 kJ/mol) compared to that with no iron (32.31 kJ/mol); and the apparent reaction orders were obtained with respect to H2SO4 concentration (1.10 and 1.36) and oxygen partial pressure (1.29 and 1.41), respectively. A comprehensive kinetic model was developed on the basis of the experimental data and the fitted leaching ratio plot; and the kinetic equations for the leaching of sphalerite catalyzed by Fe3+/Fe2+ self-precipitation were determined.

Interaction kinetics of selenium-containing compounds with oxidants

Selenium compounds have been identified as potential oxidant scavengers for biological applications due to the nucleophilicity of Se, and the ease of oxidation of the selenium centre. Previous studies have reported apparent second order rate constants for a number of oxidants (e.g. HOCl, ONOOH) with some selenium species, but these data are limited. Here we provide apparent second order rate constants for reaction of selenols (RSeH), selenides (RSeR′) and diselenides (RSeSeR’) with biologically-relevant oxidants (HOCl, H2O2, other peroxides) as well as overall consumption data for the excited state species singlet oxygen (1O2). Selenols show very high reactivity with HOCl and 1O2, with rate constants > 108 M−1 s−1, whilst selenides and diselenides typically react with rate constants one- (selenides) or two- (diselenides) orders of magnitude slower. Rate constants for reaction of diselenides with H2O2 and other hydroperoxides are much slower, with k for H2O2 being <1 M−1 s−1, and for amino acid and peptide hydroperoxides ~102 M−1 s−1. The rate constants determined for HOCl and 1O2 with these selenium species are greater than, or similar to, rate constants for amino acid side chains on proteins, including the corresponding sulfur-centered species (Cys and Met), suggesting that selenium containing compounds may be effective oxidant scavengers. Some of these reactions may be catalytic in nature due to ready recycling of the oxidized selenium species. These data may aid the development of highly efficacious, and catalytic, oxidant scavengers.

Calcium deactivation during the char-CO2 gasification and its influence on determining the apparent reaction order

CO2 gasification reactivity and the apparent reaction order of chars derived from calcium-rich and calcium-poor lignites have been investigated via thermogravimetry analysis (TGA) in the temperature range from 825 to 900 °C and the CO2 partial pressure range from 0.015 to 0.1 MPa. Chemical forms of Ca species in raw and partially-gasified chars are characterized via X-ray diffraction (XRD). Results indicate that CaO carbonation during the char-CO2 gasification is a direct cause of Ca deactivation, which shows temperature and pressure dependence and follows the equilibrium regularity of CO2 over CaCO3 at different temperatures. The Ca in lignite chars plays a catalytic role at the CO2 partial pressures below 0.1 MPa at temperatures of 875 and 900 °C, while Ca deactivation occurred when the CO2 partial pressures are above 0.05 MPa at 825 °C and above 0.075 MPa at 850 °C. On the one hand, this fact suggests that Ca deactivation exhibits temperature and pressure dependence. On the other hand, char gasification may follow different catalytic mechanisms in the CO2 partial pressure range from 0.015 to 0.1 MPa, from which the determination of the apparent reaction order is less reasonable. The coefficient of determination (R2) reflects the goodness of r-PCO2 fitting, which becomes poor with the increase of CO2 partial pressure when CaO carbonation takes place. Choosing an appropriate CO2 pressure range for a given temperature is necessary to eliminate the effects of Ca deactivation on the determination of gasification reactivity and the apparent reaction order. The apparent reaction order of chars determined at conditions without Ca deactivation increases as the gasification temperature decreases.

Catalysis at Metal/Oxide Interfaces: Density Functional Theory and Microkinetic Modeling of Water Gas Shift at Pt/MgO Boundaries

The impact of metal/oxide interfaces on the catalytic properties of oxide-supported metal nanoparticles is a topic of longstanding interest in the field of heterogeneous catalysis. The significance of the metal/oxide interaction has been shown to vary according to both the inherent reactivity of the metal nanoparticle and the properties of the oxide support, with effects such as the metal d-band center, the nanoparticle shape, and the reducibility of the oxide believed to contribute to the overall system reactivity. In recent years, the water gas shift (WGS) reaction, wherein carbon monoxide and water are converted to carbon dioxide and hydrogen, has emerged as a model chemistry to probe the molecular-level details of how catalysis can be promoted in such environments, and this reaction is the focus of the present contribution. Using a combination of periodic Density Functional Theory calculations and microkinetic modeling, we present a comprehensive analysis of the WGS mechanism at the interface between a quasi-one dimensional platinum nanowire and an irreducible MgO support. The nanowire is lattice matched to the MgO support to remove spurious strain at the metal/oxide interface, and reactions both on the nanowire and at the three-phase boundary itself are considered in the mechanistic analysis. Additionally, to elucidate the consequences of adsorbate–adsorbate interactions on the WGS chemistry, an ab-initio thermodynamic analysis of CO coverage is performed, and the impact of the higher coverage CO states on the reaction chemistry is explicitly evaluated. These results are combined with detailed calculations of adsorbate entropies and dual-site microkinetic modeling to determine the kinetically significant features of the WGS reaction network which are subsequently, validated through experimental measurements of apparent reaction orders and activation barrier. The analysis demonstrates the important role that the metal/oxide interface plays in the reaction, with the water dissociation step being facile at the interface compared to the pure metal or oxide surfaces. Further, explicit consideration of CO interactions with other adsorbates at the metal/oxide interface is found to be central to correctly determining reaction mechanisms, rate determining steps, reaction orders, and effective activation barriers. These results are captured in a closed-form Langmuir–Hinshelwood model, derived from a simplified version of the complete microkinetic analysis, which reveals, among other results, that the celebrated carboxyl mechanism of Mavrikakis and coworkers is the governing pathway when accounting for reaction-relevant CO coverages.

Degree of rate control and De Donder relations – An interpretation based on transition state theory

We describe sensitivities of elementary steps as salient parameters in determining the rate determining character of elementary steps within a reaction network and develop a formalism wherein the overall composite reaction is described by an apparent rate-determining step that is a sensitivity-weighted average of the elementary steps that comprise the reaction network. Reaction parameters—apparent reaction orders, apparent enthalpy and entropy of activation—of the composite reaction network are determined within the framework we develop by application of transition state theory to the apparent rate-determining step. From this formalism we develop methods for determination of surface coverages by measuring only reaction orders, methods for discrimination between proposed mechanisms, a proof that the kinetic degrees of rate control sum to unity, and a proof for the relationship between fractional coverages and thermodynamic degrees of rate control. Two complementary formalisms for identifying rate-limiting transition states are broadly employed in chemical kinetics—De Donder relations based on assessing the thermodynamic driving forces of elementary steps during reaction and degrees of rate control based on knowledge of the kinetics of elementary reaction steps. The formalism developed herein unifies these two strategies to elucidate in the most general case a relationship between the thermodynamic driving forces of elementary steps captured by the reversibilities and the kinetic and thermodynamic degrees of rate control.

Physicochemical analysis and kinetic study of orange bagasse at higher heating rates

The present work investigates the thermal degradation behaviour of orange bagasse that was pyrolysed in a thermogravimetric analyser at four heating rates 25, 50, 75 and 100 °C min−1 respectively under a constant N2 flow rate of 0.1 L min−1. Along with thermal degradation, the physicochemical properties of orange bagasse were determined by proximate, ultimate, compositional analysis and high heating value. The analysis results indicated that the orange bagasse has low moisture and high volatile matter content which gave a better HHV of 17.26 MJ kg−1. Other analysis like FT-IR, EDX, XRD, SEM and BET also helped in investigating the physicochemical properties of orange bagasse. Using three different kinetic models namely Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW) and Coats-Redfern the kinetic parameters like apparent activation energy (Ea) and reaction order (n), correlation values (R2) and pre-exponential factor (A) were determined by optimising the thermogravimetric data of orange bagasse. The two kinetic models KAS and OFW methods helped in calculating the mean apparent activation energy of the orange bagasse which was 112.90 and 123.24 kJ mol−1 respectively. The experimental data were in good agreement with the orange bagasse kinetics simulated data. From the results of the above analysis and kinetic study, it can be said that the orange bagasse has the potential to become a pyrolysis feedstock.

Activity differences of rutile and anatase TiO2 polymorphs in catalytic HBr oxidation

This article investigates the activity of TiO2-rutile and TiO2-anatase polymorphs in the catalytic HBr oxidation, which is an enabling process to close the halogen loop in bromine-mediated transformation of natural gas to high-value chemicals and liquid fuels. The evaluation of rutile-, anatase-, and rutile-anatase TiO2 catalysts, exhibiting the variable specific surface areas, revealed that anatase phase is also active in this reaction. Nonetheless, in contrast to photocatalytic processes in which anatase is typically more active than rutile, rutile exhibits ca. 2–5 times higher intrinsic rates of HBr oxidation than anatase. Thereby, the apparent activation energies and reaction orders with respect to HBr, O2, and H2O display similar values for the two polymorphs. The activity differences were rationalized by density functional theory analysis, which showed that HBr oxidation follows a similar defect-driven mechanism over the most stable rutile (110) and anatase (101) surfaces. Herein, HBr activates the catalyst through a self-doping mechanism that involves the substitution of surface oxygen by bromine with the concomitant reduction of Ti4+ to Ti3+ centers. This forms a defect level that is placed in the band gap and allows for the O2 activation on the catalyst surface. While the HBr adsorption and H2O desorption display a similar energy profiles on both polymorphs, the O2 activation and Br2 evolution are more facile over rutile compared to anatase surface due to shorter distances between the coordinatively unsaturated Ticus sites and easier reduction of Ti4+ centers upon product desorption, respectively.

A Combined Thermochemical and Microbial Process for Recycling Polylactic Acid Polymer to Optically Pure l-Lactic Acid for Reuse

Polylactic acid polymer (PLA) produced from renewable resources can be recycled at the end of life to constituent monomer, optically pure lactic acid (LA), by a combination of chemical and biological processes. Efficient application of this closed loop of LA-PLA plastics-LA can minimize accumulation of plastics waste that pollute land and oceans. Temperature-dependent hydrolysis of PLA in water to LA follows apparent first order decay kinetics after a short lag. A modified Gompertz equation can explain the overall hydrolysis process. Alkali increased the rate of hydrolysis of PLA and reduced the length of lag period compared to water alone. The stoichiometry of base added to LA released was 1.0. The highest lactic acid yield was 0.95 g g−1 of PLA. d-LA in the syrup obtained after hydrolysis of PLA-plastics was removed using an engineered Escherichia coli to produce a l-LA syrup with an optical purity ≥ 99%. These results show that thermochemical hydrolysis of PLA-based plastics to LA with optimum amount of base followed by bio-based purification to l-LA is an effective method of recycling PLA-plastics for reuse.

The potential use of torrefied Nigerian biomass for combustion applications

Many countries are seeking to expand their use of solid biomass for electricity and heat generation. Nigeria, too, is exploring its own potential energy crops and indigenous residues. The use of this biomass for energy production is, however, limited by factors such as high moisture content, low bulk and low energy density. This study examines the torrefaction and combustion properties of four readily available Nigerian woody biomass, Gmelina arborea, Terminalia superba, Nauclea diderrichii, Lophira alata and a residue, palm kernel expeller (PKE). They are considered for their suitability for use in large scale power stations, especially as pulverized fuels.The Fuels were torrefied at 270 and 290 °C for either 30 or 60 min, and assessed for pyrolysis and combustion characteristics in comparison to their untreated counterparts. Energy densities of the woods improved from 19.2 to 21.2 MJ/kg for the raw fuels to 21.5–24.6 MJ/kg for the torrefied fuels. The milling behaviour of the torrefied fuels improved upon torrefaction, especially for Nauclea; however, torrefaction had very little effect on the grindability of PKE. The apparent first order kinetics for pyrolysis were determined by thermogravimetric analysis (TGA). After torrefaction, the fuels become less reactive; Nauclea and Gmelina were the most reactive fuels, whilst PKE was the least reactive. The combustion behavior of selected fuels was visually examined in a methane air flame. This showed that torrefaction resulted in shorter ignition delay, shorter duration of volatile combustion and longer duration of char burn out.

Reaction Mechanism of Vapor-Phase Formic Acid Decomposition over Platinum Catalysts: DFT, Reaction Kinetics Experiments, and Microkinetic Modeling

A combination of periodic density functional theory (DFT, PW91-GGA) calculations, reaction kinetics experiments, and mean-field microkinetic modeling is used to derive insights on the reaction mechanism and determine the nature of the active site under reaction conditions for the vapor-phase decomposition of formic acid (FA, HCOOH) over Pt/C catalysts. Microkinetic models formulated using DFT energetics derived on the clean Pt(100) and Pt(111) required large parameter adjustments to reproduce the experimentally measured apparent activation energies and reaction orders. Further, these models predicted high surface coverage of adsorbed carbon monoxide (CO*), inconsistent with the environment of the active site in the DFT calculations on the clean surfaces. Consequently, we reperformed DFT calculations for the entire reaction network on partially CO*-covered (4/9 monolayer, ML) Pt(111) and Pt(100). The resultant microkinetic models, with thermochemistry and kinetics explicitly dependent on CO* coverage, were able to reproduce the experimentally determined activation energies and reaction orders, in addition to being self-consistent in CO* coverage. Our results suggest that Pt(100) is likely poisoned by CO* under typical reaction conditions and does not contribute significantly to the experimentally observed reactivity. Instead, we find that Pt(111) better represents the active site for FA decomposition reaction on Pt/C catalysts. The optimized model on 4/9 ML CO*-covered Pt(111) suggests that the reaction occurs via the carboxyl (COOH*) intermediate and that the spectator CO*-assisted pathways play a significant role under reaction conditions. This study underscores the importance of spectator species on the energetics and the mechanism of a catalytic reaction and their key role in developing a model that better addresses the nature of the active site under realistic catalytic reaction conditions.

The effect of molecular structure of polyphenols on the kinetics of the trapping reactions with methylglyoxal

Reaction kinetics for the reactions between four polyphenols (trans-resveratrol, apigenin, kaempferol and fisetin) and methylglyoxal (MGO) were determined at pH 7.4 and 37 °C, and the effect of functional groups of polyphenols on MGO trapping ability was examined. Reaction products of polyphenols with MGO were characterized by HPLC-MS/MS. The apparent second order rate constants for the reaction of MGO with trans-resveratrol, apigenin, kaempferol and fisetin were (2.7 ± 0.2) × 10−2 M−1 s−1, (4.4 ± 0.4) × 10−3 M−1 s−1, (6.3 ± 0.2) × 10−2 M−1 s−1, and (3.6 ± 0.1) × 10−3 M−1 s−1, respectively. The rate constants were used to evaluate the possible competition between MGO with nucleophilic sites on proteins and polyphenols at concentrations relevant to UHT milk. Combining this information with solubility and flavour of the polyphenols, it was concluded that kaempferol could effectively trap MGO and hereby inhibit Maillard reactions in UHT milk.

Mechanism of nitrite hydrogenation over Pd/γ-Al2O3 according a rigorous kinetic study

The kinetics of nitrite hydrogenation over a Pd/γ-Al2O3 catalyst was studied in a semi-batch slurry reactor at atmospheric pressure, in absence of any mass transfer effects. The hydrogen concentration and pH were kept constant during an experiment by continuously flowing a gas mixture containing hydrogen and 10% v/v CO2. The kinetic experiments were performed in an unprecedented wide concentration window of nitrite and hydrogen, revealing extreme variation in the apparent orders in hydrogen and nitrite, including reaction orders in hydrogen between 2 and 0.3, whereas the order in nitrite varied between 0.4 and −0.9. The rate of reaction is almost exclusively determined by the rate of formation of N2 as the selectivity to ammonia is very low. A Langmuir-Hinshelwood mechanism with competitive adsorption is in operation. Several mechanistic pathways, as well as possible rate determining steps in those pathways, are discussed based on these observations in combination with prior knowledge on the mechanism in literature, resulting in a revised mechanistic scheme. It is concluded that formation of NH via dissociative hydrogenation of HNOH is the rate determining step, whereas molecular N2 forms via reaction of NH with either NO, NOH or HNOH. N-N bond formation via dimerization of adsorbed NO or adsorbed N can be excluded.

Synchysite-(Ce) from Cinquevalli (Trento, Italy): Stacking Disorder and the Polytypism of (Ca,REE)-Fluorcarbonates

Synchysite-(Ce) at Cinquevalli occurs as fine needles intergrown with quartz in quartz-dikes and in association with altered K-feldspar and oxidized chalcopyrite as major constituents. Synchysite-(Ce) [Ca1.00(Ce0.43La0.26Nd0.17Y0.07Pr0.04Sm0.02Gd0.01)Σ=1.00(CO3)2(F0.58(OH)0.42)], shows an overgrowth rim of bastnäsite-(Ce) [(Ce0.34La0.25Nd0.17Pb0.07C a0.06Y0.06Pr0.04S m0.02Gd0.01)Σ=1.00C O3(F0.75(OH)0.25)]. Unit cell refinement of synchysite (C2/c) and bastnäsite (P62c) led to a = 12.272(4), b = 7.100(2), c = 18.640(5) Å, β = 102.71(5)°, and a = 7.085(1), c = 9.746(2) Å, respectively. Polysomatic faults are sporadic, but polytypic disorder is widespread. High resolution transmission electron microscopy images taken along [100] or ⟨130⟩ show an apparent order and the related diffraction patterns are streak-free. Conversely, along [010] or ⟨110⟩, a high density of stacking faults is observed and the related diffraction patterns show hhl rows with h ≠ 3n affected by streaks. No ordered domain larger than a few unit cells was detected. The stacking sequence of (Ca,REE)-fluorcarbonates can be compared with subfamily-B mica polytypes (2M2, 2O and 6H), which are characterized by n·60° (n = odd) rotations. Subfamily-A polytypes (1M, 2M1 and 3T), characterized by n·60° (n = even) rotations, should not be possible. Synchysite, characterized by ±60° rotations, can be likened to the 2M2 polytype.