Now showing items 1-20 of 105
Next PageAbstract: | Dimethylacetals of ketones; cyclohexanone, acetophenone, and benzophenone have been prepared by reacting ketones with methanol under mild reaction conditions. Large pore zeolites (H-Y and its rare earth metal, Ce3+, La3+, and RE3+ modified forms), and mesoporous clay (K-10 montmorillonite and its cerium exchanged counterpart) with regular pore structure, silica and silica-alumina have been used as catalysts. Clay catalysts are found to be much more active than zeolites, thanks to slightly bigger pore size. The nature of the pores of the solid acid catalysts determine acetalization efficiency of a particular catalyst. As evidenced by the reaction time studies, the catalyst decay is greater over the zeolites than over the clays. Carrying out the reaction with ketones of different molecular sizes it is shown that K-10 clays and rare earth exchanged H-Y zeolites are promising environmentally friendly catalysts for their use in the production fine chemicals. |
URI: | http://dyuthi.cusat.ac.in/purl/2257 |
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Dyuthi-P00049.pdf | (273.9Kb) |
Abstract: | Three enzymes, α-amylase, glucoamylase and invertase, were immobilized on acid activated montmorillonite K 10 via two independent techniques, adsorption and covalent binding. The immobilized enzymes were characterized by XRD, N2 adsorption measurements and 27Al MAS-NMR spectroscopy. The XRD patterns showed that all enzymes were intercalated into the clay inter-layer space. The entire protein backbone was situated at the periphery of the clay matrix. Intercalation occurred through the side chains of the amino acid residues. A decrease in surface area and pore volume upon immobilization supported this observation. The extent of intercalation was greater for the covalently bound systems. NMR data showed that tetrahedral Al species were involved during enzyme adsorption whereas octahedral Al was involved during covalent binding. The immobilized enzymes demonstrated enhanced storage stability. While the free enzymes lost all activity within a period of 10 days, the immobilized forms retained appreciable activity even after 30 days of storage. Reusability also improved upon immobilization. Here again, covalently bound enzymes exhibited better characteristics than their adsorbed counterparts. The immobilized enzymes could be successfully used continuously in the packed bed reactor for about 96 hours without much loss in activity. Immobilized glucoamylase demonstrated the best results. |
URI: | http://dyuthi.cusat.ac.in/purl/2264 |
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Dyuthi-P00057.pdf | (233.7Kb) |
Abstract: | The surface acidity and basicity of mixed oxides of Zr and Y and their mixed oxides have been determined by titration method using Hammett indicators. The acid base properties are evaluated on a common scale of acid strength. Liquid phase reduction of cyclohexanone has been selected as a model reaction to correlate catalytic activity. |
URI: | http://dyuthi.cusat.ac.in/purl/2307 |
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Dyuthi-P00075.pdf | (267.0Kb) |
Abstract: | The electron donor properties of Pr6O11 activated at 300. 500 and 800°C are reported from the studies on adsorption of electron acceptors of various electron affinity (7. 7, 8, 8-tetracyanoquinodimethane. 2, 3. 5, 6-tetrachloro-l, 4-benzoquin one. p-dinitrobenzene. and m-dinitrobenzene) in three solvents (acetonitrile, 1,4-dioxan and ethyl acetate). The extent of electron transfer during adsorption is understood from magnetic measurements and ESR spectral data. The corresponding data on mixed oxides of Pr and Al are reported for various compositions, The acid / base properties of these oxides are determined using a set of Hammett indicators. |
URI: | http://dyuthi.cusat.ac.in/purl/2288 |
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Dyuthi-P00069.pdf | (261.9Kb) |
Abstract: | The surface acidity and basicity of binary oxides of Zr with Ce and La are determined using a series of Hammet indicators and Ho,,max values are reported. The generation of new acid sites habe been ascribed to the charge imbalance of M1-O-M2 bonds, where M1 and M2 are metal atoms. Both Bronsted and Lewis acid sites contribute to the acidity of the oxides |
URI: | http://dyuthi.cusat.ac.in/purl/2290 |
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Dyuthi-SS72.pdf | (177.0Kb) |
Abstract: | The electron donor properties of Nd2O3 activated at 300, 500 and 800°C were investigated through studies on the adsorption of electron acceptors of various electron affinities - 7, 7, 8,8-tetracyanoquinodimethane (2.84 eV). 2, 3, 5, 6-tetrachloro-l , 4-benzoquinone (2.40 eV). p-dinitrobenzene (1.77 eV), and m-dinitrobenzene (1.26 eV) in solvents acetonitrile and 1, 4-dioxan. The extent of electron transfer during adsorption has been found from magnetic measurements and electronic spectral data. The corresponding data on mixed oxides of neodymium and aluminium are reported for various. compositions. The acid-base properties of catalysts were also determined using a set of Hammett indicators. |
URI: | http://dyuthi.cusat.ac.in/purl/2228 |
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Dyuthi-SS32.pdf | (270.0Kb) |
URI: | http://dyuthi.cusat.ac.in/purl/1719 |
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Dyuthi-T0016.pdf | (1.710Mb) |
Abstract: | The pillared montmorillonite has been prepared by exchanging Na+ in the interlayer of montmorillonite with Al hydroxy cation followed by calcination. Pillared clays are also prepared after exchanging Na' ions with Ce, La, Sm-ions and then pillarcd with aluminium oxides, The surface characterisation of the prepared catalysts has been done using XRD and surface area measurements. To probe the acidic property of the system, temperature programmed desorption (TPD) of NH, has been done. Toluene alkylation by benzyl chloride has been carried out for the evaluation of catalytic activity. The most active system is found to be mixed Al/Zr pillarcd montrnorillonite. |
URI: | http://dyuthi.cusat.ac.in/purl/2161 |
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Dyuthi-P0006.pdf | (270.4Kb) |
Abstract: | The acidity of the various rare-earth exchanged zeolite-Y catalysts has been examined by titration method using Hammett indicators and is correlated with the catalytic activity of the samples in the benzylation of 0-xylene. |
URI: | http://dyuthi.cusat.ac.in/purl/2164 |
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Dyuthi-SS08.pdf | (168.8Kb) |
Abstract: | Surface acidity/Basicity of mixed oxides of La and Zn activated at three different temperatures were determined. The data have been correlated with the catalytic activity for liquid phase reduction of cyclohexanone in isopropanol. |
URI: | http://dyuthi.cusat.ac.in/purl/2309 |
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Dyuthi-SS78.pdf | (288.8Kb) |
Abstract: | The surface acidity/ basicity of TiO2 (rutile) and its sulphate modified form have been determined by titration method using Hammett indicators after activation at different temperatures. The electron donating properties of these oxides are also studied from the adsorption of electron acceptors of different electron affinity values. The data have been correlated with the catalytic activity of these oxides towards esterification of acetic acid using n-butanol, reduction of cyclohexanone in isopropanol and oxidation of cyclohexanol in benzophenone. Catalytic activity for esterification and oxidation reaction parallels the acidity while that for reduction reaction parallels the basicity of these oxides. |
URI: | http://dyuthi.cusat.ac.in/purl/2162 |
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Dyuthi-P0007.pdf | (215.2Kb) |
Abstract: | The changes in surface acidity/basicity and catalytic activity of cerium oxide due to surface modification by sulphate ion have been investigated. Electron donor properties of both the modified and unmodified oxides have been studied using electron acceptors of various electron affinity values, viz. 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro--l, 4-benzoquinone. p-dinitrobenzene and m-dinitrobenzene in order to find out whether the increase in acidity on suphation is due to the generation of new acidic sites or they are formed at the expense of some of the basic sites. The surface acidity/basicity has been determined using a set of Hammett indicators. The data have been correlated with the catalytic activity of the oxides for esterification of acetic acid using l-butanol, reduction of cyclohexanone with 2- propanol and oxidation of cyclohexanol using benzophenone. |
URI: | http://dyuthi.cusat.ac.in/purl/2165 |
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Dyuthi-SS09.pdf | (305.5Kb) |
Abstract: | The surface electron donor properties of sulphate modified stannic oxide have been determined from the adsorption of electron acceptors of various electron affinities on the oxide surface. The acid base properties of stannic oxide have been determined by titration method using Hammett indicators. Catalytic activities of the oxide for esterification of acetic acid using n-butanol.reduction of cyclohexanone in 2-propanol and oxidation of cyclohexanol with benzophenone have been studied. The data have been correlated with the surface electron donor properties of these oxides. The activity for reduction and oxidation decreases and that for esterification reaction increases on modification with sulphate ion. It has heen found that electron donating capacity decreased when stannic oxide was modified with sulphate ion. |
Description: | Note:Indian Journal of Chemistry Vol. 37A, August 1998, pp. 669 - 673 |
URI: | http://dyuthi.cusat.ac.in/purl/2146 |
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Dyuthi-P0004.pdf | (329.8Kb) |
URI: | http://dyuthi.cusat.ac.in/purl/1725 |
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Dyuthi-T0017.pdf | (1.946Mb) |
Abstract: | Alkylation of phenol with methanol has been carried out over Sn-La and Sn-Sm mixed oxides of varying compositions at 623 K in a vapour phase flow reactor. It is found that the product selectivity is greatly influenced by the acid-base properties of the catalysts. Ortho-cresol formation is favoured over catalysts with weak acid sites whereas formation of 2,6-xylenol occurs in the presence of stronger acid sites. The cyclohexanol decomposition reaction and titrimetric method using Hammett indicators have been employed to elucidate the acid-base properties of the catalysts. |
Description: | Indian Journal of Chemistry Vol. 38A, December 1999, pp. 1253-1255 |
URI: | http://dyuthi.cusat.ac.in/purl/2147 |
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Dyuthi-P0005.pdf | (224.0Kb) |
Abstract: | The electron donating properties of La2O3 activated at 300, 500 and 800·C and its mixed oxides with alumina are reported from the studies on adsorption of electron acceptors of varying electron affinity on La203. The electron acceptors with their electron affinity values given in parenthesis are: 7,7,8,8-tetracyanoquinodimethane (2.84 eV), 2,3,5,6-tetrachloro-I,4-benzoquinone (2.40 eV) and p-dinitrobenzene(l.77eV). The basicity of the oxide has been determined by titration with n-butylamine and Ho.max values are reported. The limit of electron transfer from the oxide to the electron acceptor is between 2.40 and 1.77 eV. It is observed that La203 promotes the surface electron properties of alumina without changing its limit of electron transfer. |
URI: | http://dyuthi.cusat.ac.in/purl/2217 |
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Dyuthi-SS22.pdf | (236.1Kb) |
Abstract: | In this paper, a novel application of solid acid catalysts in the Beckmann rearrangement of E,E-cinnamaldoxime in the synthesis of an important heterocyclic compound; isoquinoline is reported. E,E-Cinnamaldoxime under ambient reaction conditions on zeolite catalysts underwent Beckmann rearrangement to produce isoquinoline in yields of ca. 86–95%. Cinnamonitrile and cinnamaldehyde were formed as by-products. LaH-Y zeolite produces maximum amount of the desired product (yield 95.6%). However, the catalysts are susceptible for deactivation due to the basic nature of the reactants and products, which neutralize the active sites. H-Y zeolite is more susceptible (22% deactivation in 10 h) for deactivation compared to the cerium-exchanged counterpart (18% deactivation in 10 h). Thus, the optimal protocol allows isoquinoline to be synthesised in excellent yields through the Beckmann rearrangement of cinnamaldoxime. The reaction is simple, effective, does not involve any other additives, and environmentally benign. |
URI: | http://dyuthi.cusat.ac.in/purl/2315 |
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Dyuthi-SS83.pdf | (457.2Kb) |
Abstract: | In this venture three distinct class of catalysts such as, pillared clays and transition metal loaded pillared clays , porous clay heterostructures and their transition metal loaded analogues and DTP supported on porous clay heterostructures etc. were prepared and characterized by various physico chemical methods. The catalytic activities of prepared catalysts were comparatively evaluated for the industrially important alkylation, acetalization and oxidation reactions.The general conclusions drawn from the present investigation are Zirconium, iron - aluminium pillared clays were synthesized by ion exchange method and zirconium-silicon porous heterostructures were Summary and conclusions 259 prepared by intergallery template method. Transition metals were loaded in PILCs and PCHs by wet impregnation method. Textural and acidic properties of the clays were modified by pillaring and post pillaring modifications. The shift in 2θ value to lower range and increase in d (001) spacing indicate the success of pillaring process. Surface area, pore volume, average pore size etc. increased dramatically as a result of pillaring process. Porous clay heterostructures have higher surface area, pore volume, average pore diameter and narrow pore size distribution than that of pillared clays. The IR spectrum of PILCs and PCHs are in accordance with literature without much variation compared to parent montmorillonite which indicate that basic clay structure is retained even after modification. The silicon NMR of PCHs materials have intense peaks corresponding to Q4 environment which indicate that mesoporous silica is incorporated between clay layers. Thermo gravimetric analysis showed that thermal stability is improved after the pillaring process. PCH materials have higher thermal stability than PILCs. In metal loaded pillared clays, up to 5% metal species were uniformly dispersed (with the exception of Ni) as evident from XRD and TPR analysis. Chapter 9 260 Impregnation of transition metals in PILCs and PCHs enhanced acidity of catalysts as evident from TPD of ammonia and cumene cracking reactions. For porous clay heterostructures the acidic sites have major contribution from weak and medium acid sites which can be related to the Bronsted sites as evident from TPD of ammonia. Pillared clays got more Lewis acidity than PCHs as inferred from α- methyl styrene selectivity in cumene cracking reaction. SEM images show that layer structure is preserved even after modification. Worm hole like morphology is observed in TEM image of PCHs materials In ZrSiPCHS, Zr exists as Zr 4+ and is incorporated to silica pillars in the intergallary of clay layers as evident from XPS analysis. In copper loaded zirconium pillared clays, copper exists as isolated species with +2 oxidation state at lower loading. At higher loading, Cu exists as clusters as evident from reduction peak at higher temperatures in TPR. In vanadium incorporated PILCs and PCHs, vanadium exist as isolated V5+ in tetrahedral coordination which is confirmed from TPR and UVVis DRS analysis. In cobalt loaded PCHs, cobalt exists as CoO with 2+ oxidation state as confirmed from XPS. Cerium incorporated iron aluminium pillared clay was found to be the best catalyst for the hydroxylation of phenol in aqueous media due to the additional surface area provided by ceria mesopores and its redox properties. Summary and conclusions 261 Cobalt loaded zirconium porous clay heterostructures were found to be promising catalyst for the tertiary butylation of phenol due to higher surface area and acidic properties. Copper loaded pillared clays were found to be good catalyst for the direct hydroxylation of benzene to phenol. Vanadium loaded PCHs catalysts were found to be efficient catalysts for oxidation of benzyl alcohol. DTP was firmly fixed on the mesoporous channels of PCHs by Direct method and functionalization method. DTP supported PCHs catalyst were found to be good catalyst for acetalization of cyclohexanone with more than 90% conversion. |
URI: | http://dyuthi.cusat.ac.in/purl/4977 |
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Dyuthi-T2048.pdf | (6.606Mb) |
Abstract: | Surface acidity of phosphate modified La2O3,CeO2 and SnO2 has been estimated by titrimetric Method using Hammett Indicators.Mixed Oxides of tin and lanthanum have also been prepared and subjected to phosphate modification.Surface characterizartion of the samples has been carried out using XRD, surface area,thermal analysis and IR spectroscopy. Phosphate content in the samples has been chemically estimated. The catalytic activity for benzylation and esterification reaction has also been investigated. |
URI: | http://dyuthi.cusat.ac.in/purl/2214 |
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Dyuthi-SS17.pdf | (406.4Kb) |
Abstract: | Vapour phase methylation of phenol is carried out over La2O3 supported vanadia systems of various composition. The structural features and physico chemical characterisation of the catalysts are investigated. Orthovanadates are formed in addition to surface vanadyl species on the metal oxide support. No V2O5 crystallites are detected. The acid base properties of the oxides are studied by Hammett indicator method and decomposition of cyclohexanol.The data are correlated with the catalytic activity and selectivity of the products. Ring alkylation is found to be predominant over these catalysts. |
URI: | http://dyuthi.cusat.ac.in/purl/2203 |
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Dyuthi-SS12.pdf | (327.2Kb) |
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