A.V. Ramaswamy

Photoemission studies of polymorphic CaCO3 materials

Abstract The surface analysis of polymorphic calcium carbonate (CaCO3) compounds, namely, calcite, aragonite, and vaterite were carried out by X-ray photoelectron spectroscopy (XPS). XPS results clearly demonstrate that vaterite is different from the other two and exhibit a low binding energy (BE) for all its constituent elements. It is attributed to the perpendicular orientation of CO32− to ab plane in vaterite. Aragonite shows less calcium and more oxygen and indicates the surface is carbonate terminated. Intergrowth of calcite and aragonite and natural dolomite samples were also analysed and compared with the above CaCO3 compounds. Ca:Mg=3 suggest that the dolomite surface is dominated by Ca.

Hydroxylation of phenol over Sn-silicalite-1 molecular sieve : solvent effects

Tin-silicalite-1 (MFI) prepared by hydrothermal synthesis has been used as catalyst in the hydroxylation of phenol with aqueous H2O2. Isolated Sn4+ ions which are probably attached to the defect silanols are active in this reaction. At optimum conditions, a H2O2 efficiency of 70% and a ortho to para product ratio of 1.6 have been achieved. The solvent used has a strong influence on the activity. The UV-Vis spectral studies indicate that acetone and acetonitrile probably coordinate strongly with Sn4+ centers preventing the solvolysis of the SiOSn units and the formation of peroxo intermediate. Methanol probably causes the cleavage of SiOSn bond to form SiOH and SnOMe species. Water was found to be an efficient solvent. The formation of EPR active radical ion in presence of H2O2 and H2O and its attenuation in presence of acetone, acetonitrile and methanol support the above conclusion.

Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions

Abstract Tin-containing, medium pore molecular sieves (Si/Sn ratios above 40) with MEL structure have been syntheszed hydrothermally and characterized by a variety of techniques. Changes in unit cell volume (XRD) account for about 20% of Sn 4+ ions in possible tetrahedral positions. 119 Sn MAS-NMR spectra, however, indicate that these are mostly in octahedral coordination. Framework IR spectra show an absorption at 970 cm −1 which is associated with Si O Sn vibration. Despite the uncertainty of the environment of the Sn 4+ ions in the silicalite structure, these tin-silicates are found to be quite active in the hydroxylation of phenol and toluene with aqueous H 2 O 2 as oxidant. The product distribution suggests that most of the Sn 4+ ions are located within the channels of the MEL structure.

Factors affecting the preparation of alumina pillared montmorillonite employing ultrasonics

In the preparation of alumina pillared clays, the intercalation step is shown to be completed within a few minutes using ultrasonics, and such materials show enhanced textural properties and improved thermal stability. The role of ultrasonics and various preparative parameters that govern the preparation of alumina pillared montmorillonite are presented. This includes the effect of exchangeable cations (Na, Ca, La), three different pillaring precursors, the concentration of pillaring species, and the concentration of the clay in suspension. It is shown that the exchangeable cations and their mode of binding influence the diffusional rates of the pillaring species. When different pillaring precursors are employed, not much variation in the textural properties of pillared clays is noticed. However, their optimum concentration is essential. It is also observed that this method can handle a concentrated clay suspension for pillaring with alumina. From the kinetics of calcium exchange experiments during pillaring, it was observed that the exchange under conventional conditions is completed instantaneously, while under ultrasonic treatment only 26% of Ca2+ exchange took place instantaneously and further exchange occurred only after ultrasonic treatment. From these observations, it is proposed that the role of ultrasonics in the present synthesis is the acceleration of diffusion of the intercalating aluminium pillaring species followed by an ion exchange process.

Acylation of alcohols, thiols and amines with carboxylic acids catalyzed by yttria-zirconia-based Lewis acid

Abstract A simple and efficient method has been developed for the acylation of alcohols, amines and thiols using yttria–zirconia-based Lewis acid as catalyst and carboxylic acids as acylating agent. The reaction was found to be chemoselective for the amino alcohol, 2-mercapto ethanol and 1,2-diol. Thus, using this method, acylation of an amino group in the presence of OH group, of OH group in the presence of SH, and of a primary OH group in the presence of secondary OH group has been achieved with excellent selectivity.

Sn-ZSM-12, a new, large pore MTW type tin-silicate molecular sieve: synthesis, characterization and catalytic properties in oxidation reactions

A new large pore tin-silicate analogue of zeolite ZSM-12 (MTW topology) with Si/Sn molar ratio >70 has been synthesized hydrothermally using a new template, hexamethylene bis(benzyl dimethyl ammonium hydroxide). This material exhibits an expansion in unit cell volume (XRD), an IR band at 970 cm−1 and a charge transfer band at 205 nm in the UV-Vis region indicating the presence of Si-O-Sn units with Sn4+ centers in Td configuration. Sn-ZSM-12 catalyzes the oxidation of phenol,m-cresol andm-xylene using dilute H2O2 as an oxidizing agent.

Oxidation of ethylbenzene over Ti-, V- and Sn-containing silicalites with MFI structure

The oxidation of ethylbenzene has been carried out over TS-1, VS-1 and Sn-silicalite-1 (MFI structure) using H2O2 as oxidant at 333–353 K. The major products were 1-phenylethanol and acetophenone arising from the oxidation of the side chain. Aromatic ring hydroxylation leads to the formation of ortho-andpara-hydroxy ethylbenzene as a minor side reaction. The differences in the product selectivities could be explained on the basis of the reaction intermediates. Among the three metallo-silicates, Sn-silicalite-1 is found to be the most active with an H2O2 efficiency of about 60 mol.%. The influence of various reaction parameters on the conversion and selectivity of ethylbenzene over Sn-silicalite-1 is reported.

Immobilization and characterization of copper chlorophthalocyanine on alumina-pillared montmorillonite

Alumina-pillared montmorillonite (Al-PILC) has been used as the host material for the immobilization of copper-tetra decachlorophthalocyanine (Cu-Cl14Pc) complex using ultrasonic technique. Thermogravimetric (TG)/DTG analysis, BET surface area, XRD, FT-IR and UV–VIS spectroscopic techniques have been used to characterize samples containing different concentrations of copper (0.104–0.152 wt.%) in Al-PILC. The studies reveal that Cu-Cl14Pc is present in the porous structure of Al-PILC and that the immobilized samples prepared by ultrasonication contain better-dispersed Cu-Cl14Pc compared to the sample prepared by normal agitation method. The catalytic activity for the hydroxylation of phenol to catechol and hydroquinone using the immobilized Cu-Cl14Pc and H2O2 is reported. The immobilized copper is the active center in the hydroxylation. The method of preparation and dispersion of Cu-Cl14Pc influence the catalytic activity.

Benzoylation of 1,2-dimethoxybenzene with benzoic anhydride and substituted benzoyl chlorides over large pore zeolites

Abstract The benzoylation of 1,2-dimethoxybenzene (veratrole) with benzoic anhydride and substituted benzoyl chlorides has been investigated in the liquid phase (chlorobenzene as solvent) over the H-forms of various zeolites. H-Y and H-BEA have been shown to be efficient catalysts in such a reaction, and led to the selective formation of the corresponding dimethoxybenzophenones. The effect of various experimental parameters on the initial rate of the reaction of veratrole with benzoic anhydride over H-Y zeolite has been studied, leading to propose a suitable mechanism based on the difference of adsorptions of the aromatic substrate and the acylating agent. Moreover, the study of the reaction of veratrole with a series of substituted benzoyl chlorides (4-CH3, 4-OCH3, 4-tert-butyl, 4-Cl, 2-Cl and 2-Br benzoyl chlorides, respectively) over the same H-Y zeolite led to conclude that, due to the high reactivity of the aromatic substrate, the electrophilicity of the acylating agent does not play a relevant role under the given heterogeneous conditions.

In situ 119Sn-Mössbauer spectroscopic study on MR, MEL, and MTW tin silicalites

MFI, MEL, and MTW analogue tin silicalites were studied by in situ Mossbauer spectroscopy to complement previous studies. Series of 77 and 300 K spectra were obtained from synthesized, reduced, and oxidized samples. Intensity changes of components as a function of temperature (d lnA/dT values) were also considered in addition to the usual spectral parameters (isomer shift and quadrupole splitting) to evaluate the spectra. The data obtained for Sn(IV) support neither the octahedral nor the extraframework emplacement; instead, dominance of tetrahedral coordination is supported. Upon reduction in hydrogen a Sn(II) component is formed and can be stabilized. A significant portion of Sn(II) can be reoxidized to the Sn(IV) state by a subsequent medium oxidation. In view of the respective d lnA/dT values and the stabilization of Sn(II), the structural change of edge-sharing [SnO4/2] tetrahedra is suggested to form Si-O-Sn(II)-O-Si bridges. The existence of these bridges also can be correlated with the catalytic activity of tin silicalites observed in mild oxidation processes.