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Ghosh A.,Massachusetts Institute of Technology | Basak S.,Massachusetts Institute of Technology | Wunsch B.H.,Massachusetts Institute of Technology | Kumar R.,Tata Chemicals Ltd | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2011

Striped catalysts: The effect of composition and structure on the catalytic efficiency of gold nanoparticles protected by a monolayer composed of two types of ligands differing in length (see picture) is reported. By diluting catalytically active ligand molecules with simple catalytically inactive molecules the catalytic efficiency of the particles is enhanced. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Kalita P.,Iowa State University | Kalita P.,CSIR - National Chemical Laboratory | Kumar R.,Tata Chemicals Ltd
Applied Catalysis A: General | Year: 2011

Immobilization of 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD, a bicylic guanidine base) over mesoporous material like SBA-15 has been found to be an excellent catalyst for Michael-addition of β-nitro styrene with malonate. The reactions were performed under solvent-free condition at 373 K for 9 h. A wide variety of Michael donors and acceptors were investigated. Among them, high yield of Michael product was obtained for the reaction between p-Cl-nitrostyrene with dimethyl malonate. © 2011 Elsevier B.V. All rights reserved. Source


Kalita P.,Iowa State University | Kumar R.,Tata Chemicals Ltd
Microporous and Mesoporous Materials | Year: 2012

A solvent-free versatile and efficient methodology, reported here, allows the synthesis of coumarin by hydroxyalkylation of phenols with ethyl or methyl acetoacetate (via Pechmann reaction) using trifluoromethanesulfonic acid (triflic acid) functionalised Zr-TMS (Zr-TMS, zirconia based transition metal oxide mesoporous molecular sieves) catalysts with different loadings of triflic acid over Zr-TMS (5-25 wt.%) where the total acid strength of acid functionalised Zr-TMS material is increased as increasing loading of triflic acid from 5 to 25 wt.% leading to correspond increased higher catalytic activity. © 2011 Elsevier Inc. All rights reserved. Source


Kinage A.K.,CSIR - National Chemical Laboratory | Prashar A.K.,CSIR - National Chemical Laboratory | Chaturvedi R.K.,Tata Chemicals Ltd
Materials Characterization | Year: 2011

The growth of hydrothermally stable ordered meso-porous silica with M41S type structure interconnected around zeolite crystals was achieved from seeds normally nucleating the crystallization of micro-porous zeolite. The solid state NMR and FT-IR showed species like Si(OSi)3OH and Si(OSi) 2(OH)2 (or Q3 and Q2 sites, respectively) are formed during first hydrothermal treatment with surfactant and NaOH. These species and surface silanol group of zeolite crystal condense to give meso-porous silica structure interconnected around zeolite crystal during re-crystallization at lower pH. Resulting meso-micro-porous hybrid material is found to be highly active, selective and stable in the synthesis of 2-(phenylamino) ethanol from aniline and ethylene carbonate compare to parent ZSM-5 and pure MCM-41. © 2011 Elsevier Inc. All rights reserved. Source


Kalita P.,Georgia Institute of Technology | Kalita P.,CSIR - National Chemical Laboratory | Kumar R.,Tata Chemicals Ltd
Microporous and Mesoporous Materials | Year: 2012

The trifluoromethanesulfonic (trflic) acid functionalized Zr-TMS materials were synthesized and characterized by powder XRD, N 2-sorption, elemental analysis, FTIR spectroscopy, NH 3-TPD, and 13C CP MAS NMR techniques. The samples with different loadings of triflic acid (TFA) over Zr-TMS (5-25 wt.%) were synthesized. The acid density of TFA functionalised Zr-TMS (Zr-TMS-TFA) materials increased with loading of TFA from 5 through 25 wt.%. The catalytic performance of Zr-TMS-TFA catalysts was evaluated in Michael addition of 3-methylindole to α,β-unsaturated ketones under liquid phase and solvent free reaction conditions. For example, the conversion of 3-methylindole increased with increasing loading of TFA from 38 through 87%. The selectivity of C2-adduct compared to that of N-adduct also increased with increasing loading of TFA. The higher conversion was observed in the case of electron-withdrawing group containing indoles with higher selectivity of C-adduct. The catalysts were found to be reusable. © 2012 Elsevier Inc. All rights reserved. Source

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