National Chemical Laboratory

About: National Chemical Laboratory is a facility organization based out in Pune, Maharashtra, India. It is known for research contribution in the topics: Catalysis & Nanoparticle. The organization has 8891 authors who have published 14837 publications receiving 387600 citations.

Location of Protons in Anhydrous Keggin Heteropolyacids H3PMo12O40 and H3PW12O40 by 1H{31P}/31P{1H} REDOR NMR and DFT Quantum Chemical Calculations

Abstract: HeteroPolyAcids (HPA's) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied acidic form of H(8-n)X(n+)M(12)O(40), X = Si, P and M = Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (R(P-H) = 520 +/- 20 pm) in H(3)PMo(12)O(40) and in the terminal oxygen positions (R(P-H) = 570 +/- 20 pm) in H(3)PW(12)O(40), REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.

Oxidative kinetic resolution of alcohols using chiral Mn–salen complex immobilized onto ionic liquid modified silica

Abstract: The supported ionic liquid strategy has been applied for the immobilization of chiral Mn(III) salen complex onto ionic liquid modified silica. Chiral Mn(III) salen complex was immobilized over silica through a thin film of covalently anchored imidazolium ionic liquid. These catalysts were characterized by N2 sorption, XRD, FTIR, DRUV–vis, and elemental analysis. The results showed that the chiral Mn(III) salen complex could be successfully immobilized onto the modified mesoporous materials and that the long-range mesoporous ordering of parent supports was maintained after the immobilization. The immobilized catalyst provided good enantioselectivity and activity in the heterogeneous catalysis of the oxidative kinetic resolution of secondary alcohol and can be recovered and recycled for four times without obvious loss of enantioselectivity and activity. Oxidative kinetic resolutions of meso-diols, hydroxyl ester and primary alcohol were also studied using this catalyst system.

CFD simulation of stirred tanks: Comparison of turbulence models (Part II: Axial flow impellers, multiple impellers and multiphase dispersions)

Abstract: In the first part of the review, published literature regarding the CFD modelling of single-phase turbulent flow in stirred tank reactors with radial flow impellers was critically analysed. A brief overview of different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model and large eddy simulation) as well as impeller baffle interaction models has been presented in the previous part. This part is concerned with the review of literature regarding CFD simulation of axial flow impellers. Comprehensive simulations have been carried out using various turbulence models and the model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. The strengths and weaknesses of various turbulence models for axial flow impellers is presented. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as Reynolds stress model. Literature efforts on multiple impeller systems and multiphase systems have been discussed in a separate section. Based on these results, suggestions have been made for the future work in this area. Dans la premiere partie de l'etude, on a procede a une analyse critique de la litterature concernant la modelisation de la dynamique des fluides numerique de l'ecoulement turbulent a une phase dans les reacteurs a cuve agitee dotes de turbines a ecoulement radial. Une vue d'ensemble rapide des differents modeles de turbulence (modele standard k-e, modele RNG k-e, modele aux tensions de Reynolds et simulation des grandes echelles), ainsi que des modeles d'interaction des deflecteurs de turbine, a ete presentee dans la partie precedente. Cette partie se concentre sur l'analyse de la litterature concernant la simulation de DFN de turbines a ecoulement axial. Des simulations completes ont ete effectuees en utilisant plusieurs modeles de turbulence et les predictions des modeles (de toutes les vitesses moyennes, de l'energie cinetique turbulente et de son taux de dissipation) ont ete comparees aux donnees experimentales relevees a differents endroits de la cuve. On a presente les points forts et les points faibles de plusieurs modeles de turbulence concernant les turbines a ecoulement axial. La comparaison quantitative des donnees exactes et modelisees de la production, du transport et de la dissipation de la turbulence a mis en evidence les raisons qui expliquent la reussite partielle de plusieurs modifications apportees au modele standard k-e ainsi qu'au modele aux tensions de Reynolds. Une partie distincte est consacree a la discussion des resultats indiques dans la litterature concernant les systemes a roues multiples et les systemes multiphases. Sur la base de ces resultats, des etudes a venir dans ce domaine ont ete suggerees. © 2011 Canadian Society for Chemical Engineering