Evaluation of the reactivity,selectivity and lifetime of hydrotalcite-based catalysts using isopropanol as probe molecule

Hydrotalcite catalysts derived from NiAl and NiAlMg mixed oxides were successfully prepared by coprecipitation at a constant pH of 11. Physicochemical methods were investigated to determine their structural and textural properties. Using isopropanol as a probe molecule, the acid–base properties of the catalysts were investigated, and the evaluation of reactivity, selectivity and lifetime was established.

     

Preparation and Structure Determination of SrMn2(PO4)2 and Redetermination of b ′‐Mn3(PO4)2

Pale rose single crystals of SrMn₂(PO₄)₂ were obtained from a mixture of SrCl₂ · 6 H₂O, Mn(CH₃COO)₂, and (NH₄)₂HPO₄ after thermal decomposition and finally melting at 1100 °C. The new crystal structure of strontium manganese orthophosphate [P‐1, Z = 4, a = 8.860(6) Å, b = 9.054(6) Å, c = 10.260(7) Å, α = 124.27(5)°, β = 90.23(5)°, γ = 90.26(6)°, 4220 independent reflections, R1 = 0.034, wR2 = 0.046] might be described as hexagonal close‐packing of phosphate groups. The octahedral, tetrahedral and trigonal‐bipyramidal voids within this [PO₄] packing provide different positions for 8‐ and 10‐fold [SrO_x] and distorted octahedral [MnO₆] coordination according to a formulation Mn Mn Mn Sr (PO₄)₄. Single crystals of β′‐Mn₃(PO₄)₂ (pale rose) were grown by chemical vapour transport (850 °C → 800 °C, P/I mixtures as transport agent). The unit cell of β′‐Mn₃(PO₄)₂ [P2₁/c, Z = 12, a = 8.948(2) Å, b = 10.050(2) Å, c = 24.084(2) Å, β = 120.50°, 2953 independent reflections, R1 = 0.0314, wR2 = 0.095] contains 9 independent Mn²⁺. The reinvestigation of the crystal structure led to distinctly better agreement factors and significantly reduced standard deviations for the interatomic distances.     

Magnetized cylindrically symmetric universe in general relativity

A magnetized cylindrically symmetric universe with two degrees of freedom in which the free gravitational field is Petrov type I degenerate, is obtained. The magnetic field is due to an electric current produced along the x-axis. The distribution consists of an electrically neutral perfect fluid with an infinite electrical conductivity. The behaviour of the model when magnetic field tends to zero and other physical aspects of the model are also discussed.     

Observation of phase-sensitive temporal correlations in the resonance fluorescence from two-level atoms

We have made what we believe is the first observation of phase-dependent temporal correlations in the fluorescent field emitted by coherently driven two-level atoms in free space. We measured the temporal fluctuations of the fluorescent field when the resonant driving field was in phase and out of phase with the local-oscillator field.     

Fuzzy optimization approach to component selection of fault-tolerant software system

In developing software systems, a manager’s goal is to design software using limited resources and meet the user requirements. One of the important user requirements concerns the reliability of the software. The decision to choose the right software modules (components) becomes extremely difficult because of the number of parameters to be considered while making the decision. If suitable components are not available, then the decision process is further complicated with build versus buy decisions. In this paper, we have formulated a fuzzy multi-objective approach to optimal decision “build-or-buy” for component selection for a fault-tolerant modular software system under the consensus recovery block scheme. A joint optimization model is formulated where the two objectives are maximization of system reliability and minimization of the system cost with a constraint on delivery time. An example of developing a retail system for small-and-medium-size enterprises is used to illustrate the proposed methodology.     

Inflationary Scenario in Bianchi Type I Space-Time

Inflationary scenario in Bianchi Type I space-time is discussed. To get the deterministic model of the universe, it has been considered that the energy-momentum tensor of particles ∼T ⁴, almost vanishes in the course of expansion of universe and total energy-momentum tensor reduces to vacuum stress tensor. This leads to a∼e ^Ht where a is scale factor and H the Hubble constant and effective potential V(φ)=constant where φ is Higg’s field and n is a constant. The physical and geometrical aspects of the model in the context of inflationary scenario are also discussed.     

Kinetic determination of silver at trace level based on its catalytic effect on a ligand substitution reaction

It is observed that Ag(I) catalyzes the rate of substitution of phenylhydrazine (PhNHNH₂) into hexacyanoferrate(II), producing a cherry red colored complex, [Fe(CN)₅PhNHNH₂]³⁻. The reaction was monitored at 488 nm leading to the formation of the complex under the conditions: [Fe(CN)₆]⁴⁻ (5.0 × 10⁻³ mol dm⁻³), PhNHNH₂ (2.0 × 10⁻³ mol dm⁻³), temperature (25 ± 0.1 °C), pH (2.8 ± 0.02), and ionic strength, I (0.02 mol dm⁻³), (KNO₃). Under optimum conditions, absorbance at fixed times (A _t ) is linearly related to Ag(I) in the concentration range 10.79–97.08 ng cm⁻³, in the presence of several diverse ions. The highest percentage error and relative standard deviations in the entire range of Ag(I) determination are found to be 2.5% and 0.16, with a detection limit of 8.75 ng cm⁻³ of silver(I). The experimental accuracies expressed in terms of percentage recoveries are in the range of 97.87–102.50. The method was successfully applied for the determination of Ag(I) in a few synthetic samples and found to be in good agreement with those obtained from atomic absorption spectrophotometry (AAS). The validity of the proposed method has also been tested for Ag(I) determination in spiked drinking water samples. The present catalytic kinetic method (CKM) is highly sensitive, selective, reproducible, and inexpensive. A review of recently published catalytic spectrophotometric methods for determination of Ag(I) has also been presented for comparison.     

Development of a Creatinine Sensor Based on a Molecularly Imprinted Polymer‐Modified Sol‐Gel Film on Graphite Electrode

An electrochemical creatinine sensor based on a molecularly imprinted polymer (MIP)‐modified sol‐gel film on graphite electrode was developed. The surface coating of MIP over sol‐gel was advantageous to obtain a porous film with outwardly exposed MIP cavities for unhindered selective rebinding of creatinine from aqueous and biological samples. A fast differential pulse, cathodic stripping voltammetric response of creatinine can be obtained after being preanodized the sensor in neutral medium containing appropriate amount of creatinine at +1.8 V versus SCE for 120 s. A linear response over creatinine concentration in the range of 1.23 to 100 μg mL^?1 was exhibited with a detection limit of 0.37 μg mL^?1 (S/N=3).