Spinel systems with the composition of Cu 1−x Zn x Cr 2 O 4 [x = 0 CCr, x = 0.25 CZCr-1, x = 0.5 CZCr-2, x = 0.75 CZCr-3 and x = 1 ZCr] were prepared by homogeneous co-precipitation method and were characterized by X-ray diffraction (XRD) and FT-IR spectroscopy. Elemental analysis was done by EDX, and surface area measurements by the BET method. The redox behavior of these catalysts in cyclohexane oxidation at 243 K using TBHP as oxidant was examined. Cyclohexanone was the major product over all catalysts with some cyclohexanol. 69.2% selectivity to cyclohexanol and cyclohexanone at 23% conversion of cyclohexane was realized over zinc chromite spinels in 10 h.
Iron and mixed iron aluminium pillared montrnorillonites prepared by partial hydrolysis method were subjected to room temperature
exchange with transition metals of the first series. The resulting materials were characterised by different spectroscopic techniques
and surface area measurements. About 1-3% transition metals were incorporated into the porous network. The structural
stability of the porous network was not affected by exchange. XRD and AI NMR spectroscopy evidenced the presence of iron
substituted Al13 like polymers in FeAl pillared systems. Acidity and basicity benefited much as a result of metal exchange. Acidity
and basicity were quantified by model reactions, viz., cumene cracking and cyclohexanol decomposition respectively. The presence
of basic sites in otherwise acidic pillared clays, though diminutive in amount can be of much importance in acid base catalysed
reactions.
Sreekumar, K; Thomas, Mathew; Mirajkar, S P; Sugunan, S; Rao, B S(Elsevier, 2000)
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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.
Jyothi, T M; Sugunan, S; Rao, B S(Catalysis Letters, 2000)
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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.
Rare earth exchanged Na–Y zeolites,
H-mordenite, K-10 montmorillonite clay and amorphous
silica-alumina were effectively employed for the
continuous synthesis of nitriles. Dehydration of benzaldoxime
and 4-methoxybenzaldoxime were carried
out on these catalysts at 473 K. Benzonitrile (dehydration
product) was obtained in near quantitative yield
with benzaldoxime whereas; 4-methoxybenzaldoxime
produces both Beckmann rearrangement (4-methoxyphenylformamide)
as well as dehydration products
(4-methoxy benzonitrile) in quantitative yields. The
production of benzonitrile was near quantitative under
heterogeneous reaction conditions. The optimal protocol
allows nitriles to be synthesized in good yields
through the dehydration of aldoximes. Time on stream
(TOS) studies show decline in the activity of the catalysts
due to neutralization of acid sites by the basic reactant
and product molecules and water formed during the
dehydration of aldoximes.
One-pot acetalizations of cyclohexanone. acetophenone and benzophenone were carried out using methanol over H-montmorillonite clay
(a mesoporous material). silica, alumina, and different zeolites such as HFAU-Y.HBeta, H-ZSM-5, and H-mordenite. In all the cases a single
product-the corresponding dimethylacetal-was obtained in high yields. Hemiacetal formation was not observed with any catalyst. A
comparison of catalytic activity indicated that montmorillonite K-10 is the most active catalyst for the reaction. As evidenced by the reaction
time studies, the catalyst decay is greater over the zeolite catalyst than over the clay.
Sugunan, S; Renuka, N K(Indian Journal of Chemistry, April , 2002)
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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
The electron-donor properties of Sm2O3 activated at 300, 500, and 800°C are reported from studies on the adsorption of electron acceptors of various electron affinities (electron affinity values in eV are given in parentheses): 7,7,8,8-tetracyanoquino-dimethane (2.84), 2,3,5,6-tetrachloro-1,4-benzoquinone (2.40), p-dinitrobenzene (1.77), and m-dinitrobenzene (1.26) in acetonitrile and 1,4-dioxane. The extent of electron transfer during the adsorption was determined from magnetic measurements. The acid-base properties of Sm2O3 at different activation temperatures are reported using a set of Hammett indicators. Electron donor-acceptor interactions at interfaces are important in elucidating the adhesion forces.
Sugunan, S; Jalaja, J M(Indian Journal of Chemistry, March , 1995)
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Abstract:
The electron donating properties of Ce02 and its mixed
oxides with alumina have been determined from the studies
of adsorption of electron acceptors of various electron
affinities on the surface of these oxides. The catalytic
activity of these oxides towards some reactions such as
oxidation of alcohols and reduction of ketones have been
Correlated with their surface electrondonor properties. The
surface acidity/basicity of these oxides have also been
determined by titration method using a set of Hammett
indicators.
The catalytic activity of Perovskite-type mixed oxides (LaCo03 . PrCo03 and SmCo03 ) for the
reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-Ponndorf-Verley reduction)
has been studied. The data have been correlated with the surface electron donor properties
of these mixed oxides.
Sugunan, S; Devika Rani, G(Indian Journal of Chemistry, November , 1993)
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Abstract:
The adsorption of electron acceptors, viz.,7,7,8,8-tetracyanoquinodimethane(TCNQ), 2,3,5,6-tetrachloro-p-
benzoquinone (chloranil) and p-dinitrobenzene
(PDNB) on the surface of three rare earth oxides Y2O3,
Nd203 and Pr6O11 has been studied in acetonitrile and
dioxan. From the radical concentration on the surface
determined using ESR spectral data, the electron donor
strength of the rare earth oxides are reported.
Invertase was adsorbed onto micro-porous acid-activated montmorillonite clay (K-10) by two procedures, namely adsorption and covalent binding. The immobilized enzymes were characterized by XRD, surface area measurements and 27Al NMR. XRD measurements revealed an expansion of clay layers due to immobilization which suggests that intercalation had taken place. Surface area measurements also support this observation. 27Al NMR showed that interaction of enzyme with tetrahedral and octahedral Al changes with the immobilization procedure. Sucrose hydrolysis was performed in a batch reactor. The immobilized enzymes showed enhanced pH and thermal stabilities. Optimum pH and temperature were found to increase upon immobilization. The effectiveness factor (η) and Michaelis constant (Km) suggest that diffusional resistances play a major role in the reaction. The immobilized invertase could be stored in buffer of pH 5 and 6 at 5 °C without any significant loss in activity for 20 days.
Invertase was immobilized on acid activated montmorillonite via two independent procedures, adsorption and covalent binding. The immobilized enzymes were characterized by XRD, NMR and N2 adsorption measurements and their activity was tested in a fixed bed reactor. XRD revealed that the enzyme was situated on the periphery of the clay and the side chains of different amino acid residues were involved in intercalation with the clay matrix. NMR demonstrated that tetrahedral Al was linked to the enzyme during adsorption and the octahedral Al was involved during covalent binding. Secondary interaction of the enzyme with Al was also observed. N2 adsorption studies showed that covalent binding of enzymes caused pore blockage since the highly polymeric species were located at the pore entrance. The fixed bed reactor proved to be efficient for the immobilized invertase. The optimum pH and pH stability improved upon immobilization. The kinetic parameters calculated also showed an enhanced efficiency of the immobilized systems. They could be used continuously for long period. Covalently bound invertase demonstrated greater operational stability.
Glucoamylase was immobilized on acid
activated montmorillonite clay via two different procedures
namely adsorption and covalent binding. The
immobilized enzymes were characterized by XRD,
NMR and N2 adsorption measurements and the
activity of immobilized glucoamylase for starch
hydrolysis was determined in a batch reactor. XRD
shows intercalation of enzyme into the clay matrix
during both immobilization procedures. Intercalation
occurs via the side chains of the amino acid residues,
the entire polypeptide backbone being situated at the
periphery of the clay matrix. 27Al NMR studies
revealed the different nature of interaction of enzyme
with the support for both immobilization techniques.
N2 adsorption measurements indicated a sharp drop in
surface area and pore volume for the covalently bound
glucoamylase that suggested severe pore blockage.
Activity studies were performed in a batch reactor. The
adsorbed and covalently bound glucoamylase retained
49% and 66% activity of the free enzyme respectively.
They showed enhanced pH and thermal stabilities. The
immobilized enzymes also followed Michaelis–Menten
kinetics. Km was greater than the free enzyme that was
attributed to an effect of immobilization. The immobilized
preparations demonstrated increased reusability
as well as storage stability.
Glucoamylase from Aspergillus Niger was immobilized on montmorillonite clay (K-10) by two procedures, adsorption and covalent binding. The immobilized enzymes were characterized using XRD, surface area measurements and 27Al MAS NMR and the activity of the immobilized enzymes for starch hydrolysis was tested in a fixed bed reactor (FBR). XRD shows that enzyme intercalates into the inter-lamellar space of the clay matrix with a layer expansion up to 2.25 nm. Covalently bound glucoamylase demonstrates a sharp decrease in surface area and pore volume that suggests binding of the enzyme at the pore entrance. NMR studies reveal the involvement of octahedral and tetrahedral Al during immobilization. The performance characteristics in FBR were evaluated. Effectiveness factor (η) for FBR is greater than unity demonstrating that activity of enzyme is more than that of the free enzyme. The Michaelis constant (Km) for covalently bound glucoamylase was lower than that for free enzyme, i.e., the affinity for substrate improves upon immobilization. This shows that diffusional effects are completely eliminated in the FBR. Both immobilized systems showed almost 100% initial activity after 96 h of continuous operation. Covalent binding demonstrated better operational stability.
The effect of residual cations in rare earth metal modified faujasite–Y zeolite has been monitored using magic angle spinning NMR spectral analysis and catalytic activity studies. The second metal ions being used are Na+, K+ and Mg+. From a comparison of the spectra of different samples, it is concluded that potassium and magnesium exchange causes a greater downfield shift in the 29Si NMR peaks. Also, lanthanum exchanged samples show migration behavior from large cages to small cages, which causes the redistribution of second counter cations. It is also observed that Mg2+ causes the most effective migration of lanthanum ions due to its greater charge. The prepared systems were effectively employed for the alkylation of benzene with 1-octene in the vapor phase. From the deactivation studies it is observed that the as-exchanged zeolites possess better stability towards reaction condition over the pure HFAU zeolite.
Suja, H; Deepa, C S; Sreeja Rani, K; Sugunan, S(Indian Journal of Chemistry, August , 2003)
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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.
Cyclohexanol decomposition activity of supported vanadia catalysts is ascribed to the high surface area, total acidity and interaction between supported vanadia and the amorphous support. Among the supported catalysts, the effect of vanadia over various wt% V2O5 (2–10) loading indicates that the catalyst comprising of 6 wt% V2O5 exhibits higher acidity and decomposition activity. Structural characterization of the catalysts has been done by techniques like energy dispersive X-ray analysis, X-ray diffraction and BET surface area. Acidity of the catalysts has been measured by temperature programmed desorption using ammonia as a probe molecule and the results have been correlated with the activity of catalysts.
Invertase was immobilised on microporous montmorillonite K-10 via adsorption and covalent binding. The immobilised enzymes were tested for sucrose hydrolysis activity in a batch reactor. Km for immobilised systems was greater than free enzyme. The immobilised forms could be reused for 15 continuous cycles without any loss in activity. After 25 cycles, 85% initial activity was retained. A study on leaching of enzymes showed that 100% enzyme was retained even after 15 cycles of reuse. Leaching increased with reaction temperature. Covalent binding resisted leaching even at temperatures of 70 °C.