Phosphonate‐Modified UiO‐66 Brønsted Acid Catalyst and Its Use in Dehydra‐Decyclization of 2‐Methyltetrahydrofuran to Pentadienes

Phosphorus‐modified all‐silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well‐defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO‐66 topology, achieved by attaching phosphonic acid to the 1,4‐benzenedicarboxylate ligand and using it to form UiO‐66‐PO₃H₂ by post‐synthesis modification. Characterization reveals that UiO‐66‐PO₃H₂ retains stability similar to UiO‐66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra‐decyclization of 2‐methyltetrahydrofuran (2‐MTHF). For the later reaction, the reported catalyst exhibits site‐time yields and selectivity approaching that of phosphoric acid on all‐silica zeolites. Using solid‐state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.     

Alteration in Cross Diffusivities Governs the Nature and Dynamics of Spatiotemporal Pattern Formation

Realizing spatiotemporal patterns out of a chemical reaction diffusion system remains an experimental challenge owing to the difficulty in overcoming the stringent condition of diffusion driven instability. Herein, by considering the spatially extended Gray-Scott model system, we have investigated how the cross diffusivities of the reactants involved influence the nature and dynamics of spatiotemporal patterns. Our study unravels that in absence of diffusion driven instability, spatially inhomogeneous patterns can be obtained for the Gray-Scott model system, and unstable time dependent patterns can be stabilized just by adjusting cross diffusivities of the reactants. Interestingly, the effect of cross diffusion in presence of the diffusion driven instability can differentially alter the speed of pattern formation, and potentially modify the nature of the spatiotemporal patterns obtained under different parametric conditions. Experimental verification of our findings may allow us to observe spatiotemporal patterns beyond the regime of classical Turing instability.     

Temporal Instability of Acoustic Wave in a Semiconductor Plasma Medium under Momentum Mismatched Condition

Physics of the Solid State - Temporal instability of acoustic wave is investigated in an infinite semiconductor plasma using classical hydrodynamic approach. We consider a homogeneous semiconductor...     

Determination of isotopic composition of boron

Investigations were carried out on the determination of isotopic composition of boron using Cs₂BO ₂ ⁺ ion and thermal ionisation mass spectrometry. The results show distinct advantage over the normally used Na₂BO ₂ ⁺ ion.     

A comparative adsorption study with different industrial wastes as adsorbents for the removal of cationic dyes from water

Four adsorbents have been prepared from industrial wastes obtained from the steel and fertilizer industries and investigated for their utility to remove cationic dyes. Studies have shown that the adsorbents prepared from blast furnace sludge, dust, and slag have poor porosity and low surface area, resulting in very low efficiency for the adsorption of dyes. On the other hand, carbonaceous adsorbent prepared from carbon slurry waste obtained from the fertilizer industry was found to show good porosity and appreciable surface area and consequently adsorbs dyes to an appreciable extent. The adsorption of two cationic dyes, viz., rhodamine B and Bismark Brown R on carbonaceous adsorbent conforms to Langmuir equation, is a first-order process and pore diffusion controlled. As the adsorption of dyes investigated was appreciable on carbonaceous adsorbent, its efficiency was evaluated by comparing the results with those obtained on a standard activated charcoal sample. It was found that prepared carbonaceous adsorbent exhibits dye removal efficiency that is about 80-90% of that observed with standard activated charcoal samples. Thus, it can be fruitfully used for the removal of dyes and is a suitable alternative to standard activated charcoal in view of its cheaper cost.     

Vibration and deflection analysis of thin cracked and submerged orthotropic plate under thermal environment using strain gradient theory

Nonlinear Dynamics - Based on a non-classical plate theory, a nonlinear analytical model is proposed to analyze transverse vibration of thin partially cracked and submerged orthotropic plate in the...     

Nighttime enhancements in TEC near the crest of northern equatorial ionization anomaly during low solar activity period

Enhancement in nighttime total electron content (TEC) near the crest of equatorial ionization anomaly at Bhopal (Geog. 23.2°N, 77.4°E, and MLAT 14.2°N) has been studied for the solar minimum period March 2005- November 2006. TEC data recorded by GPS Ionospheric Scintillation and TEC Monitor (GISTM) GSV4004A receiver is used for the study and results are presented in the paper. More than 10% increase in TEC with respect to background content is considered for analysis. Out of total 138 enhancements, 65 observed during pre midnight hours and 73 during post midnight hours. It is observed that nighttime enhancement in TEC at Bhopal occurs in all seasons; it is more frequent during summer, less during equinox and least during winter months. The enhancement in nighttime TEC can be observed both in geomagnetic disturbed time and in quiet time. We found that mean peak amplitude for pre-midnight TEC enhancement are more in equinox and less in winter, while in post-midnight TEC enhancement it is highest in summer and less in winter. Post-midnight enhancements have smaller peak amplitude as compared to pre-midnight. Also the most probable values for pre- and post-midnights are 4.4 TECU and 2.17 TECU respectively. The percentage occurrence of nighttime TEC enhancement does not show any dependence on solar activity whereas the peak amplitude depends on solar activity. The percentage occurrence of nighttime TEC enhancement decreases as the magnetic activity increases whereas there is no such dependency found with peak amplitude. It is also observed that majority of nighttime TEC enhancements are occurred without scintillation. The localised nighttime TEC enhancements near the crest of equatorial ionization anomaly region have been observed most of the nights during the period of study.     

Generalized power symmetric stochastic matrices

We characterize stochastic matrices which satisfy the equation where are positive integers.

     

Kinetics and mechanism of micellar effects upon the hydrolysis of 0-(2,4-dinitrophenyl) cyclohexanone oxime

A modification in the reaction mechanism of 0-(2,4-dinitrophenyl)cyclohexanone Oxime with OH^– in 30% aqueous methanol is suggested. The cationic micelles of cetyltrimethyl ammonium bromide enhance the reaction by a factor ofca. 3. The pseudo first order rate constant at the micellar surface was found to be 10.9×10^–4 s^–1 at 35±0.1°C. Anionic and nonionic micelles inhibit the rate of the reaction. Bromide ion inhibits the catalysis, which indicates that catalysis is partially due to a concentration effect. The catalytic efficiency increases with decreasing [OH^–), which implies that the efficiency of the surfactant could be related to some standard parameter(s).

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0-(2,4-)-- OH^– 30%- . . 3. - 10.9·10^{–4 –1} 35±0.1°C. . . , - . - [OH^–], , - - .