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Kale S.S.,Leibniz Institute for Catalysis at the University of Rostock | Armbruster U.,Leibniz Institute for Catalysis at the University of Rostock | Eckelt R.,Leibniz Institute for Catalysis at the University of Rostock | Bentrup U.,Leibniz Institute for Catalysis at the University of Rostock | And 4 more authors.
Applied Catalysis A: General | Year: 2016

The heterogeneously catalyzed esterification (acetylation) of glycerol toward triacetin in batch mode in presence of toluene as entrainer was studied. Silicotungstic acid, tungstophosphoric acid and phosphomolybdic acid as heteropolyacids (HPAs) supported on silica, alumina or silica-alumina were used as catalysts. The course of the reaction was found to be very sensitive to the nature of the HPA as well as the support. Solid characterization by Raman spectroscopy, XRD, and pyridine-FTIR revealed that only combinations of tungsten-based HPAs and silica support were able to preserve the structure of active component throughout the preparation process, which was essential to obtain active and selective catalysts. The interaction between HPA and support was decisive for stability and dispersion of the catalytically active species. With the best performing catalyst H4SiW12O40/SiO2, selectivity to triacetin reached 71% at complete conversion within 24 h. The high selectivity to triacetin is attributed the Brønsted acidic sites originated from stabilized Keggin structure and continuous removal of water during course of reaction. Toluene is able to form azeotropic mixtures with water and acetic acid and keeps the reaction temperature below the boiling point of acetic acid. Thus, water-free reaction conditions can be established. The catalyst was reusable; however, the activity and selectivity towards triacetin slightly decreased in a repetition run due to loss of active sites. © 2016 Elsevier B.V.


Kale S.,University of Rostock | Umbarkar S.B.,CSIR - National Chemical Laboratory | Dongare M.K.,CSIR - National Chemical Laboratory | Dongare M.K.,Mojj Engineering Systems Ltd. | And 3 more authors.
Applied Catalysis A: General | Year: 2015

Esterification of glycerol with acetic acid in the presence of toluene as an entrainer was performed over acidic Amberlyst ion-exchange resins in a batch reactor. Toluene continuously removed the reaction water, thus the chemical equilibrium was effectively shifted; the selectivity for the most desired product triacetin was dramatically increased. The influence of reaction conditions such as reaction time, acetic acid: glycerol molar ratio and catalyst amount were investigated. More than 95% selectivity to triacetin at complete glycerol conversion was obtained. The ion-exchange resin catalysts were reusable in subsequent runs, but due to some deactivation the triacetin yields deteriorated. © 2014 Elsevier B.V. All rights reserved.


More P.M.,CSIR - National Chemical Laboratory | More P.M.,CSIR - Central Electrochemical Research Institute | Nguyen D.L.,CNRS Laboratory of Catalysis and Solid State Chemistry | Granger P.,CNRS Laboratory of Catalysis and Solid State Chemistry | And 5 more authors.
Applied Catalysis B: Environmental | Year: 2015

Bimetallic Ag-Au/Al2O3 catalyst was synthesised by successive impregnation of 1% Au and 1% Ag on in-house prepared high surface area alumina (450m2/g). The corresponding monometallic catalysts were also prepared by loading 1% Ag or 1% Au on the same high surface area alumina for comparison. The catalysts were characterised by various physico-chemical techniques and tested for SCR activity under lean burn engine exhaust conditions. Ag-Au/Al2O3 catalyst prepared by successive impregnation method showed considerably higher NO reduction (100%) to N2 compared to 1% Au/Al2O3 (70%) whereas the activity was comparable with that of 1% Ag/Al2O3 (96%). The effect of various pretreatments on SCR activity of Ag-Au/Al2O3 was studied and pretreatment at 250°C in flow of hydrogen was found to give the best results with 100% NO conversion to N2 at 353°C. Further ageing of the catalyst under reaction feed at 500°C resulted in considerable increase in low temperature activity of bimetallic catalyst with ~40% NO conversion at 222°C. Even though the SCR activity of pretreated Ag-Au/Al2O3 and Ag/Al2O3 were comparable, after ageing the Ag-Au/Al2O3 showed significantly higher NO conversion (95%) compared to Ag/Al2O3 (83%) and Au/Al2O3 (70%). The formation of H2 and CO due to steam reforming of higher hydrocarbon (decane) was evidenced at the temperature of highest deNOx activity. Detailed investigation of the textural properties of the pretreated and aged catalysts showed presence of well dispersed metallic Au and Agn δ+ clusters after pretreatment in hydrogen at 250°C. © 2015 Elsevier B.V.


More P.M.,CSIR - National Chemical Laboratory | More P.M.,CSIR - Central Electrochemical Research Institute | Nguyen D.L.,CNRS Laboratory of Catalysis and Solid State Chemistry | Dongare M.K.,CSIR - National Chemical Laboratory | And 9 more authors.
Applied Catalysis B: Environmental | Year: 2015

This study emphasizes the importance of the preparation method for bimetallic Au-Ag catalysts supported on alumina in the selective reduction of NOx by hydrocarbons with gas feed compositions representative of diesel fuelled engine exhaust gas. An optimal balance between oxidative and reductive surface properties is obtained when Au and Ag are successively introduced. Significant re-dispersion processes take place when the catalyst runs at 500°C leading to a gain in activity at low temperature and ascribed to a better interaction between Au and Ag species. Co-precipitation leads to a preferential formation of intermetallic Au-Ag particles which is detrimental to the catalytic performances. Aging at 500°C leads to a significant particle sintering and a strengthening of the metallic character. © 2014 Elsevier B.V.


More P.M.,CSIR - National Chemical Laboratory | More P.M.,CSIR - Central Electrochemical Research Institute | Jagtap N.,CSIR - National Chemical Laboratory | Kulal A.B.,CSIR - National Chemical Laboratory | And 5 more authors.
Applied Catalysis B: Environmental | Year: 2013

A series of magnesia doped Ag/Al2O3 catalysts were prepared by modified impregnation method using boehmite as alumina precursor. The prepared catalysts were characterized and tested for the SCR of NOx using propene as reductant under lean condition. Doping of magnesia improved the low temperature catalytic activity for HC-SCR of NOx as well as sulfur tolerance. Maximum 98% NO conversion with 100% selectivity for N2 was obtained at 350°C with 7% Mg doping to Ag/Al2O3. The improvement in low temperature activity and the sulfur tolerance has been correlated to decreased acidity after addition of magnesia to alumina support. In situ FTIR study showed that the deactivation in the presence of SO2 was due to the sulfation of silver and aluminum sites in Ag/Al2O3 catalyst, however its formation was suppressed in case of magnesia doped Ag/Al2O3 improving its sulfur tolerance. © 2013.


Acham V.R.,CSIR - National Chemical Laboratory | Biradar A.V.,CSIR - National Chemical Laboratory | Dongare M.K.,CSIR - National Chemical Laboratory | Dongare M.K.,Mojj Engineering Systems Ltd | And 2 more authors.
ChemCatChem | Year: 2014

A one-pot synthesis of palladium nanoparticles supported on magnesium hydroxide fluoride has been performed with the fluorolytic sol-gel method. The prepared catalysts were characterized by using various physicochemical techniques. The sol-gel method led to high surface area (> 135 m2g-1), mesoporous catalysts (pore volume=0.19-0.23 cm3g-1, pore diameter= 3-5 nm) with uniformly dispersed palladium nanoparticles approximately 2 nm in diameter on the surface. The catalysts synthesized by using different concentrations of aqueous hydrofluoric acid exhibited changing surface and acidic properties. Very high dispersion of palladium on magnesium fluoride (47%) was obtained with 1 wt% palladium loading. The catalysts were used for hydrogenation of various olefins in the presence of other organic functionalities at room temperature and atmospheric hydrogen pressure. Various substituted olefins were hydrogenated with almost 100% conversion and selectivity. The catalysts were recycled efficiently over five cycles without appreciable loss in catalytic activity. There was no palladium leaching under the reaction conditions, which was confirmed by inductively coupled plasma atomic emission spectroscopy analysis. Activation of olefin on the catalyst surface could not be observed by in situ FTIR studies, indicating facile activation of hydrogen on the palladium supported on magnesium hydroxide fluoride. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ghantani V.C.,CSIR - National Chemical Laboratory | Ghantani V.C.,CSIR - Central Electrochemical Research Institute | Dongare M.K.,CSIR - National Chemical Laboratory | Dongare M.K.,Mojj Engineering Systems Ltd | And 2 more authors.
RSC Advances | Year: 2014

Calcium phosphate catalysts were prepared by co-precipitation method using calcium nitrate and mixtures of ammonium and different sodium phosphates as calcium and phosphate precursors, respectively. Depending on the phosphate precursor, the pH of the synthesis mixture changed during the catalyst precipitation. The catalyst characterisation by XRD and ICP revealed the formation of a calcium pyrophosphate structure with varying Ca/P ratio from 1.02 to 0.76 which could be correlated to the different pH of the synthesis solutions. Vapour phase dehydration of lactic acid to acrylic acid was carried out using these calcium pyrophosphate catalysts. Non-stoichiometric calcium pyrophosphate catalyst with Ca/P ratio 0.76 was found to be the most efficient catalyst among the synthesized series with 100% lactic acid conversion and 78% acrylic acid selectivity at 375 °C. The higher selectivity for acrylic acid has been correlated to the increased acidity and reduced basicity of non-stoichiometric calcium pyrophosphate compared to other stoichiometric pyrophosphates. In situ FTIR studies showed the formation of a higher amount of calcium lactate on non-stoichiometric compared to stoichiometric pyrophosphate leading to higher selectivity for acrylic acid. © the Partner Organisations 2014.


Kotbagi T.V.,CSIR - National Chemical Laboratory | Biradar A.V.,CSIR - National Chemical Laboratory | Umbarkar S.B.,CSIR - National Chemical Laboratory | Dongare M.K.,CSIR - National Chemical Laboratory | Dongare M.K.,MOJJ Engineering Systems Ltd
ChemCatChem | Year: 2013

We report the isolation, characterization, and identification of the catalytically active species formed during various acid-catalyzed reactions if silica-supported MoO3 was used as a catalyst. We have reported previously the synthesis and extensive characterization of the silica-supported MoO3 catalyst prepared by the sol-gel process with ammonium heptamolybdate and ethyl silicate-40 as molybdenum and silica precursors, respectively. The TEM images showed uniformly distributed MoO3 nanoparticles on the high-surface area mesoporous silica support and high acidity (0.9mmolg-1) by using temperature-programmed desorption of ammonia (NH3-TPD) analysis. This catalyst has already shown high activity for various acid-catalyzed reactions. To understand the nature of catalytically active species formed during the reaction, the liquid-phase esterification of acetic acid and ethanol was studied as a probe reaction with very high acid conversion (83%) in 8h. During esterification, the reaction mixture turned blue, which indicated a change in the nature of the catalyst under reaction conditions. These catalytically active species formed in the reaction mixture were isolated and extensively characterized by using FTIR, Raman, powder XRD, BET surface area, NH3-TPD, energy dispersive X-ray, and TEM analysis. The characterization results revealed the insitu formation of silicomolybdic acid on the silica surface in the presence of water, which acts as catalytically active species responsible for the acid-catalyzed reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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