A1PO4-Al2O3 catalysts with low alumina content. III. Surface basicity of catalysts obtained in aqueous ammonia

The amount of basic sites of A1PO₄-Al₂O₃ (APA1-A, 5–15 wt% Al₂O₃) catalysts at two basic strengths was measured by studying the liquid-phase adsorption of two acidic molecules (benzoic acid (BA, pK = 4.2) and phenol (PH, pKa = 9.9) from cyclohexane solutions, through the application of a spectrophotometric method. The data obtained follow the Langmuir adsorption isotherm and the monolayer coverage at equilibrium (at 298 K),X _m, is assumed as the amount of basic sites corresponding to the specific pK of the acid used as titrant. The amount of basic sites of any AlPO₄-Al₂O₃ catalyst is higher than that of AlPO₄, but lower than that of Al₂O₃. Besides, an increase in the Al₂O₃ content from 10 wt% gradually increases the basicity of the APA1-A catalyst. Moreover, calcination at increasing temperatures does not practically affect the surface basicity of APAl-A-5 and APAl-A-10 catalysts. However, for AlPO₄ content higher than 10 wt% we observe a decrease in surface basicity, this decrease depends on alumina content, i.e. it is higher as the amount of alumina increases. The basic sites of APAl-A systems catalyze the Knoevenagel condensation ofp-methoxybenzaldehyde and malononitrile at room temperature and in the absence of solvent.     

Modulation of Ultrafast Conformational Dynamics in Allosteric Interaction of Gal Repressor Protein with Different Operator DNA Sequences

Although all forms of dynamical behaviour of a protein under allosteric interaction with effectors are predicted, little evidence of ultrafast dynamics in the interaction has been reported. Here, we demonstrate the efficacy of a combined approach involving picosecond‐resolved FRET and polarisation‐gated fluorescence for the exploration of ultrafast dynamics in the allosteric interaction of the Gal repressor (GalR) protein dimer with DNA operator sequences O_E and O_I. FRET from the single tryptophan residue to a covalently attached probe IAEDANS at a cysteine residue in the C‐terminal domain of GalR shows structural perturbation and conformational dynamics during allosteric interaction. Polarisation‐gated fluorescence spectroscopy of IAEDANS and another probe (FITC) covalently attached to the operator directly revealed the essential dynamics for cooperativity in the protein–protein interaction. The ultrafast resonance energy transfer from IAEDANS in the protein to FITC also revealed different dynamic flexibility in the allosteric interaction. An attempt was made to correlate the dynamic changes in the protein dimers with O_E and O_I with the consequent protein–protein interaction (tetramerisation) to form a DNA loop encompassing the promoter segment.     

Ozone generation via the electrolysis of fluoboric acid using glassy carbon anodes and air depolarized cathodes

An electrochemical ozone generation process was studied wherein glassy carbon anodes and air depolarized cathodes were used to produce ozone at concentrations much higher than those obtainable by conventional oxygen-fed corona discharge generators. A mathematical model of the build up of ozone concentration with time is presented and compared to experimental data. Products based on this technology show promise of decreased initial costs compared with corona discharge ozone generation; however, energy consumption per kg ozone is greater. Recent developments in the literature are reviewed.Nomenclature A electrode area (m²) - Ar ^* modified Archimedes number, d _b ³ g_G/² (1 — _G) - C _{O 3 (aq)} concentration of dissolved ozone (mol m^–3) - C _{O 3 i} concentration at interface (mol m^–3) - C _{O 3 1} concentration in bulk liquid (mol m^–3) - D diffusion coefficient (m² s^–1) - E electrode potential against reference (V) - F charge of one mole of electrons (96 485 C mol^–1) - g gravitational acceleration (9.806 65 m s^–2) - i current density (A m^–2) - i ₁ limiting current density (A m^–2) - I current (A) - j material flux per unit area (mol m^–2 s^–1) - k _obs observed rate constant (mol^–1 s^–1) - k _t thermal conductivity (J s^–1 K^–1) - L reactor/anode height (m) - N _{O 3} average rate of mass transfer (mol m^–2 s^–1) - Q heat flux (J s^–1) - r _i radius of anode interior (m) - r _a radius of anode exterior (m) - r _c radius of cathode (m) - R gas constant (8.314 J K^–1 mol^–1) - S _c Schmidt number, v/D - Sh Sherwood number, k _m d _b/D = i _L d _b/zFD[O₃] - t time (s) - T _i temperature of inner surface (K) - T _o temperature of outer surface (K) - U reactor terminal voltage (V) - electrolyte linear velocity (m s^–1) - V volume (m³) - V _{O 3} volume of ozone evolved (10^–6 m³ h^–1) - z _i number of Faradays per mole of reactant in the electrochemical reaction Greek symbols _G gas phase fraction in the electrolyte - (mean) Nernst diffusion layer thickness (m) - fractional current efficiency - overpotential (V) - electrolyte kinematic viscosity (m² s^–1) - electrolyte resistivity (V A^–1 m)     

A reaction model for the electrochemical production of p-anisidine

The work examines the possibility of a simple reaction model describing a complex organic electrosynthesis, such as the formation of p-anisidine. The experimental results obey the linear relationships of the model and in consequence the kinetic constants obtained in this way define reaction behaviour. The paper demonstrates how such a model can play a useful role in the design of pilot plant experimentation. Results from a parallel plate cell fit prediction from the model.Nomenclature [X] Concentration of species X (kmol m^–3) - b Slope of Tafel plot (mV^–1) - E Electrode potential (mV) - F Faraday (C g-equiv^–1) - F Faraday based on k-equiv = 10³F (C k-equiv^–1) - i _A Partial current density for the primary reaction (A m^–2) - i _B Partial current density for the consecutive secondary reaction (A m^–2) - i _H Partial current density for the parallel secondary reaction (A m^–2) - i Total current density=i _A+i _B+i _H (A m^–2) - k Reaction rate constant (A m^–2 per kmolm^–3) - k _H Rate constant for the parallel secondary electrode reaction (A m^–2) - k _I Individual mass transfer coefficient (m s^–1) - N Flux (kmol m^–2 s^–1) - r Reaction rate (kmol m^–2 s^–1) Sufixes A Appertaining to primary electrode reaction or species A - B Appertaining to consecutive secondary electrode reaction or species B - b In the bulk of the electrolyte - H Parallel secondary electrode reaction - s Near the electrode surface     

Modeling the Transient Adsorption Process of Ternary Mixtures on Nanoporous Zeolitic Adsorbents in Batch Systems

Abstract

Transient adsorption process of a hypothetical ternary mixture constituted by a fast diffusing‐weak adsorbing (C1), a low diffusing‐strong adsorbing (C2), and a high saturation capacity species (C3) on zeolite adsorbents in a batch system was modeled by the Maxwell‐Stefan formulation in combination with the IAST mixture isotherm. When the Henry constant of C2 and C3 were K ₂=K ₃, the transient adsorption selectivity (S _i,j ) defined with the weakest‐adsorbing species used as a reference becomes higher for C3 in comparison with C2, during the entire lapse of contact time. The influence of the gas phase pressure and mixture composition on the transient adsorption selectivities basically depends on the behavior of the equilibrium selectivities (S _i,j ^eq ). The transient response of the fractional coverage (θ _i ) of C1 within the zeolite overshoots its equilibrium value. In comparison to the single adsorption profiles, the component with the highest saturation capacity (C3) is the only species of the ternary mixture that maintains its fractional coverage practically unmodified. When K ₂ >K ₃, a cross‐over between the corresponding equilibrium selectivities can occur with pressure. The use of the model based on experimental data is discussed.     

Fermentation and oxygen transfer characteristics in serine alkaline protease production by recombinant Bacillus subtilis in molasses‐based complex medium

Serine alkaline protease (SAP) production in a complex medium based on physically pretreated molasses by recombinant Bacillus subtilis carrying pHV1431::subC gene is described. The effects of oxygen transfer were investigated in 3.5 dm³ bioreactor systems with controls for agitation rate, dissolved oxygen, pH, temperature, and foam formation under two different agitation rates, ie N = 500 and 750 min^?1, and four different air flow rates, ie Q/V_R = 0.2, 0.5, 0.7, and 1.0 vvm, at a molasses concentration equivalent to initial sucrose concentration (C_So) of 20 kg m^?3. The yield values (Y_X/S, Y_X/O, Y_S/O) and maintenance coefficient of oxygen (m_O), were calculated. m_O decreased with the increase in the air‐inlet rate. Increase in oxygen transfer rate increased the rate of growth and SAP activity, and affected the cultivation time to achieve maximum expression of SAP activity. At Q/V_R = 0.5 vvm and N = 750 min^?1, SAP activity reached 2250 U cm^?3 at t = 36 h. The oxygen transfer coefficient (K_La) and oxygen uptake rate (?r_O) were measured throughout the fermentations and their variation with the oxygen transfer conditions determined. New correlations for the calculation of K_La and ?r_O are proposed. Copyright © 2004 Society of Chemical Industry     

Effect of drag-reducing polymer on the rate of mass transfer in fixed-bed reactors

Rates of mass transfer were measured for the cementation of copper from dilute copper sulphate solutions containing polyethylene oxide drag-reducing polymer on a fixed bed of zinc pellets. Starting from a Reynolds number (Re) of 550, the rate of mass transfer was found to decrease by an amount ranging from 7.5 to 51% depending onRe and polymer concentration. The percentage decrease in the rate of mass transfer increased with increasingRe, passed through a maximum atRe=1400 and then decreased rapidly with further increase inRe. The possibility of using drag-reducing polymers to reduce power consumption in fixed-bed operation was discussed in the light of the present and previous results.Nomenclature A cross-section of reactor (m²) - a specific area of bed (m²) - C copper sulphate concentration at timet (moll^–1) - C ₀ initial copper sulphate concentration (moll^–1) - D diffusivity of copper sulphate (m₂s^–1) - d _p particle diameter (m) - J _d mass transfer J-factor (StSc ^2/3) - K mass transfer coefficient (m s^–1) - L bed height (m) - Q volumetric flow rate (m³s^–1) - Re Reynolds number (V _i d _p/) - Sc Schmidt number (/_D) - St Stanton number (K/V _i) - V volume of copper sulphate solution (m³) - V _i interstitial velocity (V _s/), (ms^–1) - V _s superficial velocity (ms^–1) - bed porosity - solution viscosity (kg m s^–1) - solution density (kg m^–3) - storage tank residence time (s)     

A wall jet electrode reactor and its application to the study of electrode reaction mechanisms Part II: A general computational method for the mass transport problems involved

A numerical computational method to solve the problems of mass transport to the impinged surface of a wall-jet electrode reactor is put forward, thus providing the necessary tool for a quantitative electrochemical investigation of the mechanism of electrode processes, using a wall-jet electrode reactor as a hydrodynamic electrode system. The computational method is based on a second order-correct implicit finite difference approach and a coordinate transformation making a simple Cartesian space discretization compatible with efficient computing, thus allowing the computations to be performed on a personal computer. The computational approach is demonstrated through calculation of a single step chronoamperometric transient for a simple one electron transfer reaction and shown to be accurate by comparing the computed with experimentally determined current transients using as a model reaction the reduction of ferricyanide ions at a platinum electrode surface from a 0.01 m K₃Fe(CN)6-0.01 m K₄Fe(CN)₆ solution containing l m KCl as supporting electrolyteList of symbols a nozzle diameter (m) - C _i concentration of electroactive species i (mol m^–3) - C _i normalized concentration of electroactive species i - D _i diffusion coefficient of the electroactive species i (m² s^–1) - E electrode potential (V vs SCE) - E ₀ equilibrium potential (V vs SCE) - F Faraday's constant (C mol^–1) - dimensionless parameter, describing the distance normal to the impinged electrode - H distance between the working electrode and the tip of the nozzle (m) - I electrode current (A) - k _r constant linking the typical velocity of the wall-jet to the mean velocity in the nozzle - M flux of exterior momentum flux - v kinematic viscosity (m² s^–1) - r distance along the impinged electrode in cylindrical pole coordinates having their origin at the intersection of the jet axis and the electrode surface - R radius of the impinged electrode (m) - dimensionless time - t time (s) - v _I velocity component along the impinged electrode (m s^–1) - v _Z velocity component normal to the impinged electrode (m s^–1) - V _f volume flow rate (m^–3 s^–1) - dimensionless parameter, describing the distance normal to the impinged electrode - z distance normal to the impinged electrode in cylindrical pole coordinates having their origin at the intersection of the jet axis and the electrode surface (m)     

Mass transfer to and copper deposition on a round bar in a new type of electrolytic cell: the helix cell

High-rate electrodeposition of copper from CuSO₄-H₂SO₄ baths can be achieved by using crossflow of solution. To obtain copper layers of uniform thickness and quality, a new type of electrolytic cell, the helix cell, has been proposed. An experimental dimensionless relation has been given to describe the mass transfer to a round bar, in crossflow, in a helix cell. Moreover, the current efficiency of copper deposition has been obtained as a function of current density, flow rate of solution, temperature and weight per cent CuSO₄ in the CuSO₄-H₂SO₄ solution.Nomenclature A _e working-electrode surface area (m²) - c concentration of Cu²⁺ (mol m^-3) - c _e c at electrode surface (mol m^-3) - c _b c in bulk of solution (mol m^-3) - C constant factor (-) - d _c inner diameter of central cylinder of helix cell (mm) - d _c volumetric hydraulic diameter of helix cell (mm) - d _h width of helical slots in central cylinder of helix cell (mm) - d _s diameter of working electrode (round bar) (mm) - D _i diffusion coefficient of species i (m² s^-1) - F Faraday constant (C mol^-1) - I current (A) - k _i mass-transfer coefficient for a species i (m s^-1) - i current density (kA m^-2, A m^-2) - L _c length of working-electrode compartment of helix cell (m) - n number of electrons involved in electrode reaction (-) - n₁, n₂, n₃ constants (-) - R gas constant: R=8.31 J K^-1 mol^-1 - Re Reynolds number: Re=v _c d _h/v (-) - Sc Schmidt number: Sc=v/D (-) - Sh Sherwood number: Sh=kd _h/D - t time (s) - T temperature (K) - U _s volumetric rate of solution through the helix cell (m³ s^-1) - v _c flow rate of solution through working-electrode compartment of the helix cell (vc = U/(d _c –dw)Lc) (ms–1) - density of solution (kg m ^-3) - u dynamic viscosityofsolution (kg m-1 s-1) - v kinematic viscosity of solution (m2 s-1) - _i current efficiency for formation of a species i (-)     

Mass transfer and structure of asbestos and non-asbestos diaphragms for chlorine and caustic production

Models and equations describing aspects of diaphragm performance are discussed in view of recent experiences with non-asbestos diaphragms. Excellent control of wettability and, therefore, of the amount of gases inside the diaphragm, together with chemical resistance to the environment during electrolysis, was found to be an essential prerequisite to performances of non-asbestos diaphragms that are comparable to those of asbestos diaphragms. Equations, derived and supported by experimental evidence from previous work, are shown to describe and predict hydrodynamic permeability and ohmic voltage drop of diaphragms, even in cases where the amount of gases inside the diaphragm slowly increases during electrolysis. Current efficiency is observed to be only dependent to a slight extent on the effective electrolyte void fraction inside the diaphragm. Major effects that determine current efficiency at 2 kA m^–2 and 120 gl^–1 caustic are shown to be diaphragm thickness, pore diameter distribution and the number of interconnections between pores inside the diaphragm. A discussion on design of the structure of non-asbestos diaphragms is presented.Nomenclature B permeability coefficient (m²) - c _i,x concentration of ionic species i at position x (mol m^–3) - c _k concentration of hydroxyl ions in catholyte (mol m^–3) - CE current efficiency - d thickness of diaphragm (m) - thickness of layer (m) - D _i ionic diffusion coefficient of species i (m²s^–1) - D _e dispersion coefficient (m²s^–1) - electrolyte void fraction - E potential inside diaphragm (V) - F Faraday constant, 96487 (C mol^–1 of electrons) - F _j,i flux of ionic species i in the stagnant electrolyte inside small pores of layer j - H hydrostatic head (N m^–2) - i flux of current =j/F (mol m^–2s^–1) - j current density (A m^–2) - k _i,l constant representing diffusion in diaphragm (m²s^–1) - k ₂ constant representing migration in diaphragm (m^–1) - v _p hydraulic pore radius according to [15] (m) - N number of layers - N _j,i flux of ionic species i in layer j (mol m^–2s^–1) - P hydrodynamic permeability (m³ N^–1s^–1) - R gas constant, 8.3143 (J mol^–1 K^–1) - density of liquid (kg m^–3) - R ₀ electric resistivity of electrolyte (ohm m) - R _d electric resistivity of porous structure filled with electrolyte (ohm m) - R _m resistance of the diaphragm (ohm m²) - R _a resistance of anolyte layer (ohm m²) - R _e resistance of electrodes (ohm m²) - s specific surface of porous structure (m^–1) - s ₀ standard specific surface of solids in porous structure (m^–1) - tortuosity defined according toR _d/R ₀=/ - T absolute temperature (K) - u superficial liquid velocity (m s^–1) - U cell voltage (V) - dynamic viscosity (N s m^–2) - v kinematic viscosity (m²s^–1) - x diaphragm dimensional coordinate (m) - y radial coordinate inside pores (m) Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands, September 17th and 18th 1987.     

Factors affecting catalytic performance in yadh-catalyzed reductions in non-conventional media

The effects of parameters including water content, the amount of celite and the co-factor regeneration system on reduction of benzaldehyde to benzyl alcohol by yeast alcohol dehydrogenase (YADH) immobilized on celite in non-conventional media were investigated. Kinetic parameters (apparent) such as V_max, K_m, and k_car for different organic solvents used (butyl acetate, hexane, heptane and i-octane) were determined. K_m values for benzaldehyde increased as the solvent was varied in the following manner: butyl acetate < hexane < i-octane < heptane. The highest K_m value (20.26 mmol/L) was noted in heptane and the lowest (3.24 mmol/L) in butyl acetate. The V_max value in heptane was more than an order of magnitude higher than that in butyl acetate. Catalytic efficiencies (as expressed by k_car/K_m) ranged from 0.703 × 10^?4 L/mol · s for hexane to 0.171 × 10^?4 L/mol · s for butyl acetate. In general, linear relationships were observed between k_car/K_m and the following solvent physico-chemical constants: dielectric constant logarithm of the saturated molar solubility of water in the organic solvents, log S_w/o, logarithm of partition coefficient of organic solvent in water/octanol two-phase system, log P, Hildebrand solubility parameter, δ, and solvatochromism of pyridinium-N-phenoxide betaine dye, ET(30).     

The effect of electrolytically formed gas bubbles on ionic mass transfer at a plane vertical electrode

The mechanism which explains the increase in the rate of mass transfer through bubble evolution is not completely established. Three models have been proposed. The present work reports experimental results obtained with a cell design which can separate the contribution of the parameters defining each model.The results obtained allow one to conclude that the main contribution to the increase in the mass transfer rate is due to the macroscopic motion of the fluid caused by the ascending bubbles. A competition between the size and the number of the bubbles at different current densities would be the cause of the constant mass transfer current over a range of gas evolution rates.Nomenclature I _g total constant current applied to the generator electrode (mA) - I _i current related to the electrochemical gas evolution (mA) - I _m mass transport current (mA) - j _g total constant current density (mAcm^–2) - j _i gas evolution current density (mAcm^–2) - j _{H 2} hydrogen evolution current density (mAcm^–2) - j _i,m mass transfer current density for the i electrode (mAcm^–2) - j _m mass transfer current density (mAcm^–2) - j _l free convection limiting current density (mAc^–2) - x the distance from the origin of the hydrogen boundary layer to the test electrode (mm) - h ₁ height of the generator electrode (mm) - h ₂ height of the inert gap between electrodes (mm) - h _i height of the n electrodes (mm) - h height of the single electrode (mm) - a electrode width (mm) - diffusional boundary layer thickness (cm) - j _im difference betweenj _im.     

Electrochemical reduction of silver thiosulphate complexes Part II Mechanism and kinetics

In this paper the thermodynamic data for complex formation between Ag⁺ and S₂O_{3 2–} ions, determined previously, are applied to kinetic investigation of the reduction of silver thiosulphate complexes. Both electrochemical (linear sweep voltammetry on a rotating disc electrode) and surface analytical (Auger electron spectroscopy) techniques are used. The deposits resulting from the electrodeposition of silver thiosulphate complexes are shown to be composed of silver and to be polycrystalline. The reduction follows a mechanism involving mass and charge transfer and chemical reaction steps. The relevant kinetic parameters are calculated and a rate equation describing the kinetics of the reduction is given.List of symbols a activity (M) - c concentration (M) - j current density (A m^–2) - j _c current density of charge transfer (A m^–2) - j _m current density of mass transfer (A m^–2) - k rate constant (m s^–1) - y activity coefficient (molarity scale) - D diffusion coefficient against gradient of concentration (m² s^–1) - D diffusion coefficient against gradient of electrochemical potential (m² s^–1) - E electrode potential vs NHE (V) - I ionic strength (M) - T temperature (K) Greek symbols a transfer coefficient - _1n stability constant of Ag(S₂O₃) _n (^2n–1)- - kinematic viscosity (m² s^–1) - rotation speed of the electrode (rad s^–1) Indices b bulk of the solution - f free (= uncomplexed) - 1,n related to complex Ag(S₂O₃)_n ^(n–1) - t total Constants F Faraday constant (96486 A s mol^–1) - R universal gas constant (8.3145 Jmol^–1 K^–1)     

Applications of magnetoelectrolysis

A broad overview of research on the effects of imposed magnetic fields on electrolytic processes is given. As well as modelling of mass transfer in magnetoelectrolytic cells, the effect of magnetic fields on reaction kinetics is discussed. Interactions of an imposed magnetic field with cathodic crystallization and anodic dissolution behaviour of metals are also treated. These topics are described from a practical point of view.Nomenclature 1, 2 regression parameters (-) - B magnetic field flux density vector (T) - c concentration (mol m^–3) - c bulk concentration (mol m^–3) - D diffusion coefficient (m² s^–1) - d _e diameter of rotating disc electrode (m) - E electric field strength vector (V m^–1) - E _i induced electric field strength vector (V m^–1) - E _g electrostatic field strength vector (V m^–1) - F force vector (N) - F Faraday constant (C mol^–1) - H magnetic field strength vector (A m^–1) - i current density (A m^–2) - i _L limiting current density (A m^–2) - i _L ⁰ limiting current density without applied magnetic field (A m^–2) - I current (A) - I _L limiting current (A) - j current density vector (A m^–2) - K reaction equilibrium constant - k reaction velocity constant - k _b Boltzmann constant (J K^–1) - _{m 1}, m ₂ regression parameters (-) - n charge transfer number (-) - q charge on a particle (C) - R gas constant (J mol^–1 K^–1) - T temperature (K) - t time (s) - V electrostatic potential (V) - v particle velocity vector (m s^–1) Greek symbols transfer coefficient (–) - velocity gradient (s^–1) - _MS potential difference between metal phase and point just inside electrolyte phase (OHP) - diffusion layer thickness (m) - ₀ hydrodynamic boundary layer thickness without applied magnetic field (m) - density (kg m^–3) - electrolyte conductivity (^–1 m^–1) - magnetic permeability (V s A^–1 m^–1) - kinematic viscosity (m² s^–1) - vorticity     

The role of mass transfer in the electrolytic reduction of hexavalent chromium at gas evolving rotating cylinder electrodes

The rate of electrolytic reduction of hexavalent chromium from acidic solution at a hydrogen-evolving rotating cylinder lead cathode was studied under conditions of different current densities, Cr⁶⁺ concentrations and rotation speeds. The rate of the reaction was found to follow a first order rate equation. The specific reaction rate constant was found to increase with increasing rotation speed until a limiting value was reached with further increase in rotation speed. Mechanistic study of the reaction has shown that at relatively low rotation speeds the reduction of Cr⁶⁺ is partially diffusion controlled, at higher speeds the reaction becomes chemically controlled. The limiting specific reaction rate constant was related to the operating current density by the equationK=0.044i ^1.385. The current efficiency of Cr⁶⁺-reduction was measured as a function of current density, initial Cr⁶⁺ concentration and rotation speed. Possible practical applications are discussed.Nomenclature A electrode area (cm²) - a, b constants in Equations 5 and 13, respectively - C bulk concentration of Cr⁶⁺ at timet(M) - C _o initial concentration of Cr⁶⁺ (M) - C _i interfacial concentration of Cr⁶⁺ (M) - d cylinder diameter (cm) - D diffusivity of Cr⁶⁺ (cm² s^–1) - e _o standard electrode potential (V) - F Faraday's constant (96 487 C) - current consumed in hydrogen discharge (A) - i current density (A cm^–2) - I cell current (A) - K _l mass transfer coefficient (cm s^–1) - K _r mass transfer coefficient due to cylinder rotation (cm s^–1) - K _o natural convection mass transfer coefficient (cm s^–1) - K _g mass transfer coefficient due to hydrogen stirring (cm s^–1) - K ₂ specific reaction rate constant (cm s^–1) - K overall rate constant (cm s^–1) - m theoretical amount of Cr⁶⁺ reduced during electrolysis (g) - P gas pressure (atm) - R gas constant (atm cm³ mol^–1 K^–1) - T temperature (K) - t time (s) - V linear speed of the rotating cylinder (cm s^–1) - hydrogen discharge rate (cm³ cm^–2 s^–1) - V _s solution volume (cm³) - z electrochemical equivalent (g C^–1) - Z number of electrons involved in the reaction - Re Reynolds number (Vd/v) - Sh Sherwood number (K _r d/D) - Sc Schmidt number (v/D) - rotation speed (r.p.m.) - kinematic viscosity (cm² s^–1)     

High pyroelectric performance in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3/Al2O3 composites by design

High pyroelectric performance around human body temperature is essential for ultra-sensitive infrared detectors of medical systems. Herein, toward human health monitoring, composite ceramics (1-x)Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃/xAl₂O₃ (x = 0, 0.1, and 0.2) were designed. A metastable ferroelectric (FE) phase was induced in the anti-FE matrix by the Al₂O₃ component-induced internal stress, and in turn FE-anti-FE phase boundary was constructed. The ceramics at x = 0.2 exhibit high pyroelectric coefficient with p = 10.9 × 10⁻⁴ C·m⁻²·K⁻¹ and figures of merit with current responsivity F_i = 6.23 × 10⁻¹⁰ m·V⁻¹, voltage responsivity F_v = 12.71 × 10⁻² m²·C⁻¹, and detectivity F_d = 7.03 × 10⁻⁵ Pa^−1/2 around human body temperature. Moreover, the enhanced pyroelectric coefficients exist in a broad operation temperature range with a large full width at half maximums of 18.5°C and peak value of 29.2 × 10⁻⁴ C·m⁻²·K⁻¹ at 48.2°C. The designed composite ceramic is a promising candidate for infrared thermal imaging technology of noncontact human health monitoring system.     

Scale-up of an electrochemical cell for oxygen removal from water

In a previous paper an electrochemical method for the removal of dissolved oxygen from water was described. In that work the oxygen-rich water was passed through a three-dimensional cathode and the dissolved oxygen was reduced on the cathode surface to water. In the present study electrochemical oxygen removal and, especially, the scale-up of the deoxygenation cell were investigated. The volume of the three-dimensional cathode was enlarged and suitable cathode materials and membranes were tested. The maximum flow rate and the optimum cell voltage were determined. Finally, two cathodes were connected in parallel flow. A flow rate ten times higher than that of the former laboratory-scale cell was achieved. Over 99.95% of the dissolved oxygen was removed. No significant amount of by-products, hydrogen or hydrogen peroxide, was observed.Nomenclature A area of the membrane (m²) - D hydrodynamic permeability (g s^–1 m^–2 bar^–1) - F Faraday number (96 500 A s mol^–1) - I current (A) - I _meas measured current (A) - I _theor theoretical current (A) - M _i molecular mass of species i (g mol^–1) - flow rate (g[water] s^–1) - m _de mass of water decomposed on the anode (g) meomass of water transported through the membrane by the electroosmosis (g) - m _ev mass of water evaporated with the gaseous oxygen (g) - m _p mass of water transported through the membrane due to the pressure (g) - m _tot total mass change of the anolyte (g) - N _w water transference number (2.2) - p pressure of the gas bubble (pressure of the air, 101 300 Pa) - pH₂O water vapour pressure at room temperature (3000 Pa) - P pressure difference between catholyte and anolyte (bar) - [O₂] mass fraction of dissolved oxygen (g[O₂] g[water]^–1) - t time (s) - z _i number of electrons needed per species i     

Mass Transfer Characteristics in a Rotor‐Stator Reactor

Mass transfer characteristics in a rotor‐stator reactor in terms of the overall volumetric mass‐transfer coefficient (K_xa) using the N₂‐H₂O‐O₂ system were investigated. The effects of various operating parameters including rotation speed, liquid volumetric flow rate, and gas volumetric flow rate on K_xa were systematically examined, and a gas‐liquid mass transfer model was established to predict K_xa. Results reveal that K_xa increased with higher rotation speed, liquid volumetric flow rate, and gas volumetric flow rate. The results also confirm that the predicted values of K_xa were in agreement with the experimental values with deviation within 15 %. The results contribute to a better understanding of mass transfer characteristics in rotor‐stator reactors.     

Homo‐ and Heterobimetallic Precursor Catalysts for the Heck Reaction,and a Proposal for a General Catalytic Cooperativity Index

Homo‐ (Pd₂) and heterobimetallic (PtPd) complexes supported by a P,P‐bridging, bis(P,N‐chelating) coordination mode of the potentially hexadentate ligand 1,1‐bis[di(o‐N,N‐dimethylanilinyl)phosphino]methane (dmapm) are effective catalyst precursors for the aerobic Heck coupling of iodobenzene and styrene at 100 °C in DMF/H₂O solution containing K₂CO₃. This medium allows for trivial separation of the trans‐stilbene product which precipitates after the reaction mixture is cooled. The bimetallic precursors are more active than predicted from the sum of the activities of complexes chosen to mimic their mono‐metallic “half units,” suggesting some degree of intermetallic cooperativity during the reaction. A non‐linear dependence of initial rate on catalyst concentration implies, however, that the complexes do not remain intact, and may be involved in dissociative equilibria with non‐dmapm containing monometallic components that are more active species for the Heck coupling. The complexes are slowly degraded by oxidation at a phosphorus centre. A general index for quantifying the degree of intermetallic cooperativity during a catalytic cycle is proposed and its utility and limitations are discussed.     

Discovery of an Allosteric Ligand Binding Site in SMYD3 Lysine Methyltransferase

SMYD3 is a multifunctional epigenetic enzyme with lysine methyltransferase activity and various interaction partners. It is implicated in the pathophysiology of cancers but with an unclear mechanism. To discover tool compounds for clarifying its biochemistry and potential as a therapeutic target, a set of drug-like compounds was screened in a biosensor-based competition assay. Diperodon was identified as an allosteric ligand; its R and S enantiomers were isolated, and their affinities to SMYD3 were determined (K_D=42 and 84 μM, respectively). Co-crystallization revealed that both enantiomers bind to a previously unidentified allosteric site in the C-terminal protein binding domain, consistent with its weak inhibitory effect. No competition between diperodon and HSP90 (a known SMYD3 interaction partner) was observed although SMYD3–HSP90 binding was confirmed (K_D=13 μM). Diperodon clearly represents a novel starting point for the design of tool compounds interacting with a druggable allosteric site, suitable for the exploration of noncatalytic SMYD3 functions and therapeutics with new mechanisms of action.