| 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: | A series of ferrites having the general formula Zn1-xCoxFe2O4 (x=0, 0.2, 0.5, 0.8 and 1.0)were prepared by soft chemical route. The materials were characterized by adopting various physico-chemical methods. The reaction of aniline with methanol was studied in a fixed-bed reactor system as a potential source for the production of various methyl anilines. It was observed that systems possessing low ‘ x’ values are highly selective and active for N-monoalkylation of aniline leading to N-methylaniline. Reaction parameters were properly varied to optimize the reaction conditions for obtaining N-methylaniline selectively and in better yield. Among the systems Zn0.8Co0.2Fe2O4 is remarkable due to its very high activity and excellent stability. Under the optimized conditions N-methylaniline selectivity exceeded 98%. Even at a methanol to aniline molar ratio of 2, the yield of N-methylaniline was nearly 50%, whereas its yield exceeded 71% at the molar ratio of 5. ZnFe2O4, though executed better conversion than Zn0.8Co0.2Fe2O4 in the initial period of the run, deactivates quickly as the reaction proceeds. The Lewis acidity of the catalysts is mainly responsible for the good performance. Cation distribution in the spinel lattice influences their acido-basic properties and, hence, these factors have been considered as helpful parameters to evaluate the activity of the systems. |
| URI: | http://dyuthi.cusat.ac.in/purl/2249 |
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| Dyuthi-SS44.pdf | (385.6Kb) |
| Abstract: | The catalyst compositions of the Zn1−xCOxFe2O4 (x= 0, 0.2, 0.5, 0.8 and 1.0) spiel series possessing ‘x’ values, x less than or equal to 0.5, are unique for selective N-monomethylation of aniline using methanol as the alkylating agent. Since dimethyl carbonate (DMC) is another potential non-toxic alkylating agent, alkylation of aniline was investigated over various Zn–Co ferrites using DMC as the alkylating agent. The merits and demerits of the two alkylating agents are compared. Catalytic activity followed a similar trend with respect to the composition of the ferrospinel systems. DMC is active at comparatively low temperature, where methanol shows only mild activity. However, on the selectivity basis, DMC as an alkylating agent could not compete with methanol, since the former gave appreciable amounts of N,N-dimethylaniline (NNDMA) even at low temperature where methanol gave nearly 99% N-methylaniline (NMA) selectivity. As in the case of methanol, DMC also did not give any C-alkylated products. |
| URI: | http://dyuthi.cusat.ac.in/purl/2244 |
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| Dyuthi-SS42.pdf | (158.0Kb) |
| Abstract: | A comparative study on the anisole methylation with methanol over lanthanum-promoted Sn02 catalyst and its sulfate-doped analogue is presented. A maximum 2.6-xylenol selectivity of 82% was achieved at 400 degreeC under optimized conditions at an anisole conversion of 65% over lanthanum-promoted Sn02 catalyst. The sulfate modification resulted in the dealkylation of anisole to phenol followed by several unselective side reactions due to the creation of strong acid sites. The activity of lanthanum-modified tin oxide catalysts in the selective formation of 2.6-xylenol is ascribed to the presence of weak Lewis acid sites and comparatively stronger basic sites. |
| URI: | http://dyuthi.cusat.ac.in/purl/2170 |
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| Dyuthi-SS10.pdf | (241.3Kb) |
| 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: | Ferrospinels of nickel, cobalt and copper and their sulphated analogues were prepared by the room temperature coprecipitation route to yield samples with high surface areas. The intrinsic acidity among the ferrites was found to decrease in the order: cobalt> nickel> copper. Sulphation caused an increase in the number of weak and medium strong acid sites, whereas the strong acid sites were left unaffected. Electron donor studies revealed that copper ferrite has both the highest proportion of strong sites and the lowest proportion of weak basic sites. All the ferrite samples proved to be good catalysts for the benzoy lation of toluene with benzoyl chloride. copper and cobalt ferrites being much more active than nickel ferrite. The catalytic activity for benzoylation was not much influenced by sulphation, but it increased remarkably with calcination temperature of the catalyst. Surface Lewis acid sites, provided by the octahedral cations on the spinel surface, are suggested to be responsible for the catalytic activity for the benzoylation reaction. |
| URI: | http://dyuthi.cusat.ac.in/purl/2280 |
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| Dyuthi-SS63.pdf | (653.0Kb) |
| 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) |
| Abstract: | The present work undertakes the preparation and physico-chemical characterisation of iron promoted sulphated zirconia (SZ) with different amounts of iron loading and their application to Friedel-Crafts benzoylation of benzene, toluene and xylene under different experimental conditions, XRD and laser Raman techniques reveal the stabilisation of the tetragonal phase of zirconia and the existence of iron in highly dispersed form as Fe203 on the catalyst surface. The surface acidic properties were determined by ammonia temperature programmed desorption (TPD) and perylene adsorption, The results were supported by the TGA studies after adsorption of pyridine and 2,6-dimethylpyridine (2,6-DMP), Strong Lewis acid sites on the surface, which are evident from TPD and perylene adsorption studies. explain the high catalytic activity of the systems towards benzoylation. The experimental results provide evidence for the truly heterogeneous nature of the reaction. The studies also establish the resistance to deactivation in the metal incorporated sulphated systems. |
| URI: | http://dyuthi.cusat.ac.in/purl/2279 |
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| Dyuthi-SS62.pdf | (696.8Kb) |
| Abstract: | Sm2O3 - vanadia catalysts have been prepared by wet impregnation method using NH4VO3 solution. The surface properties of the prepared catalysts have been studied using FTIR. XRD. surface area and pore volume data. The acid-base properties of the system have been investigated by titrimetric method using Hammett indicators. adsorption of electron acceptors as well as decomposition of cyclohexanol. Phenol alkylation reaction by methanol has been carried out to investigate the catalytic activity. It has been observed that the selectivity of the products depends upon the composition of the supported system |
| URI: | http://dyuthi.cusat.ac.in/purl/2212 |
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| Dyuthi-SS15.pdf | (391.7Kb) |
| Abstract: | Physico-chemical characterization of DY203/V2O5 systems prepared through wet impregnation method has been carried out using various techniques like EDX, XRD, FTIR. thermal studies, BET surface area, pore volume and pore size distribution analysis. The amount of vanadia incorporated has been found to influence the surface properties of dysprosia. The spectroscopic results combining with X-ray analysis reveal that vanadia species exist predominantly as isolated amorphous vanadyl units along with crystalline dysprosium orthovanadate. Basicity studies have been conducted by adsorption of electron acceptors and acidity and acid strength distribution by temperature programmed desorption of ammonia. Cyclohexanol decomposition has been employed as a chemical probe reaction to examine the effect of vanadia on the acid base property of Dy2O3. Incorporation of vanadia titrates thc Lewis acid and base sites of Dy2O3, while an enhancement of Bronsted acid sites has been noticed. Data have been correlated with the catalytic activity of these oxides towards the vapour phase methylation of phenol |
| URI: | http://dyuthi.cusat.ac.in/purl/2175 |
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| Dyuthi-SS11.pdf | (825.9Kb) |
| Abstract: | The liquid-phase Friedel-Crafts acylation of toluene using benzoyl chloride as benzoylating agent has heen carried out over Nix, Mn(l-x)Fe2 O4 (x=O, 0.2, 0.4, 0.6, 0.8 and 1.0) type systems under different reaction conditions. It is observed that the systems with high 'x' values are effective for the conversion of BOC and the selective formation of 4-MBP. Selectivity for 4-MBP over MnFe2O4 is more than 90% under the optimized reaction conditions. Sites of moderate acidity is effective in calalyzing the benzoylation reaction. |
| URI: | http://dyuthi.cusat.ac.in/purl/2210 |
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| Dyuthi-SS14.pdf | (504.4Kb) |
| Abstract: | A series of supported vanadia systems have been prepared by excess solvent technique using La203 and DY203 as supports. Physical characterization has been carried out using XRD, FTIR, TG studies, BET surface area measurement, pore volume analysis etc. Cyclohexanol decomposition has been used as a test reaction for evaluating the acid base properties of the supported system. The oxidative dehydrogenation of ethylbenzene has been employed as a chemical probe reaction to examine the catalytic activity. The active species correspond to amorphous and crystalline tetrahedral vanadyl units in the supported system. |
| URI: | http://dyuthi.cusat.ac.in/purl/2211 |
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| Dyuthi-SS13.pdf | (624.7Kb) |
| Abstract: | The incorporation of transition metal oxide pillars such as those of iron and chromium along with Al2O3, pillars within the interlayers of a montmorillonite clay is investigated. The surface acidity of these catalysts has been evaluated for the first time employing the equilibrium adsorption of an electron donor, perylene, and the results are compared with those obtained by temperature programmed desorption of ammonia. The principle is based on the ability of a catalyst surface site to accept a single electron from an electron donor like perylene to form charge transfer complexes and the amount of adsorbed species is measured quantitatively by UV-vis spectroscopy. Fina1ly, an attempt has been made to correlate the acidity determined by the two independcnt methods and the catalytic activity of present systems in the benzoylation of toluene with benzoyl chloride. Incorporation of Fe and Cr has changed the properties of AI pitlared montmorillonite. Fe pillared systems have been found to be vcry good catalysts for benzoylation reaction |
| URI: | http://dyuthi.cusat.ac.in/purl/2213 |
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| Dyuthi-SS16.pdf | (817.0Kb) |
| Abstract: | Preparation of simple and mixed ferrospinels of nickel, cobalt and copper and their sulphated analogues by the room temperature coprecipitation method yielded fine particles with high surface areas. Study of the vapour phase decomposition of cyclohexanol at 300 °C over all the ferrospinel systems showed very good conversions yielding cyclohexene by dehydration and/or cyclohexanone by dehydrogenation, as the major products. Sulphation very much enhanced the dehydration activity over all the samples. A good correlation was obtained between the dehydration activities of the simple ferrites and their weak plus medium strength acidities (usually of the Brφnsted type) determined independently by the n-butylamine adsorption and ammonia-TPD methods. Mixed ferrites containing copper showed a general decrease in acidities and a drastic decrease in dehydration activities. There was no general correlation between the basicity parameters obtained by electron donor studies and the ratio of dehydrogenation to dehydration activities. There was a leap in the dehydrogenation activities in the case of all the ferrospinel samples containing copper. Along with the basic properties, the redox properties of copper ion have been invoked to account for this added activity. |
| URI: | http://dyuthi.cusat.ac.in/purl/2278 |
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| Dyuthi-SS61.pdf | (215.1Kb) |
| Abstract: | Iron pillared Montmorillonite has been synthesised and it is then wet impregnated with vanadia with different vanadia composition. These catalysts are characterised using conventional techniques such as XRD analysis,FTIR analysis and surface area and pore volume measurements. Acidity is measured using spectrophotometric monitoring of adsorption of perylene, thermogravimetric desorption of 2.6 dimethylpyridine and temperature programmed desorption of ammonia. Activity studies are done in the liquid phase. It has been concluded that Lewis acidic sites are responsible for the benzylation of toluene when the benzylating agent is benzyl chloride while Bronsted acidic sites are responsible when the reagent is benzyl alcohol. |
| URI: | http://dyuthi.cusat.ac.in/purl/2215 |
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| Dyuthi-SS18.pdf | (676.6Kb) |
| 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: | The present work investigates on the applicability of metal promoted sulphated zirconia catalysts for the hydroxylation of phenol under mild conditions. The percentage conversion and product distribution was highly sensitive towards the reaction parameters like the catalyst composition, reaction temperature, H202/ phenol ratio and the solvent used. |
| URI: | http://dyuthi.cusat.ac.in/purl/2218 |
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| Dyuthi-SS19.pdf | (643.1Kb) |
| Abstract: | Preparation and physico-chemical characterization or phosphate modified zirconia systems and their application to Friedel-Crafts benzylation and benzoylation of toluene have been reported. The influence of transition metals on the surface properties and catalytic activity has also been discussed. |
| URI: | http://dyuthi.cusat.ac.in/purl/2283 |
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| Dyuthi-SS65.pdf | (243.3Kb) |
| Abstract: | The present work attempts a systematic examination of the effect of sulphate content on the physico-chemical properties and catalytic activity of sulphated zirconia and iron promoted sulphated zirconia systems. Sulphate content is estimated by EDX analysis. The amount of sulphate incorporated has been found to influence the surface area, crystal structure and the acid strength distribution. Ammonia TPD and adsorption studies using perylene have enabled the determination of surface acidic properties. The results are supported by the thermodesorption studies using pyridine and 2,6-dimethylpyridine. The catalytic activity towards benzoylation reaction has been correlated with the surface acidity of the systems. |
| URI: | http://dyuthi.cusat.ac.in/purl/2281 |
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| Dyuthi-SS64.pdf | (1.319Mb) |
| Abstract: | Iron, aluminium and mixed iron aluminium pillared clays have been prepared by partial hydrolysis method and doped with IO% Mo, V and Cr. The samples have been characterised by XRD, FTIR and surface area and pore Volume measurements. The surface acid site distribution has been determined by temperature programmed desorption of ammonia. Vanadia incorporated systems show maximum acidity. Benzylation of o-xylene has been done as probe reaction to test catalytic activity. Benzyl chloride is a superior benzylating agent compared to benzyl alcohol in activity and selectivity. Cent percent selectivity towards monobenzylated product is obtained in all the cases. Fe pillared systems exhibit maximum activity. The catalytic activities of the systems can be correlated with the amount of strong add sites. The effects of various reaction variables on the reaction have been studied. Presence of moisture has a diminishing effect on the reaction rate. |
| URI: | http://dyuthi.cusat.ac.in/purl/2248 |
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| Dyuthi-SS41.pdf | (593.7Kb) |
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