S. Sivasanker

Studies on the synthesis of titanium silicalite, TS-1

Abstract A new procedure for the synthesis of titanium silicate-1 (TS-1) with high Ti (Si + Ti) ratios is being reported. The rationale for the method adopted and the reasons for the incorporation of more Ti (than reported by earlier workers) are discussed based on liquid-phase n.m.r. studies of the precursors and reaction mixture. The influence of various synthesis parameters like temperature, SiO 2 TiO 2 , DH − SiO 2 , and H 2 O SiO 2 , ratios, the silica source, and nature of organic additives on the synthesis of TS-1 is discussed. The TS-1 samples have been characterized by XRD, i.r. t.g./d.t.a., and SEM.

Catalytic properties of crystalline titanium silicalites III. Ammoximation of cyclohexanone

The ammoximation of cyclohexanone to cyclohexanone oxime over the titanium silicalite TS-1 with NH3 and H2O2 is reported. The ammoximation takes place at conversions exceeding 90% with selectivities greater than 99%. The influence of various catalyst and process parameters on the oximation reaction is reported. By-products from condensation reactions become significant at low concentrations of H2O2 and NH3. Possible mechanisms for the formation of the oxime and by-products are reported.

Characterization and catalytic properties of zeolite MCM-22

Characterization of MCM-22 was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis (TGA-DTA) and nuclear magnetic resonance (NMR). TGA-DTA and NMR studies indicate a strong interaction of the template with the zeolite framework. Adsorption studies indicate the internal void volume to be intermediate between the volumes of zeolite beta and ZSM-12. In catalytic reactions such as the isomerization of m-xylene, aromatization of n-hexane and transformation of methanol to hydrocarbons, the zeolite behaves like a large-pore zeolite, even though recent research has established that it is a medium-pore zeolite.

Hydroxylation of phenol over ts-2, a titanium silicate molecular sieve

Abstract The influence of different process parameters on the hydroxylation of phenol with H 2 O 2 over the titanium silicate molecular sieve TS-2 has been investigated. Apart from the primary products vis. , p - and o -dihydroxybenzenes, the corresponding quinones are also formed. Higher Ti contents in the catalyst (TS-2) and higher catalyst concentrations lower the formation of the secondary oxidation products. Solvents have an influence on the relative amounts of the two dihydroxybenzenes in the product. H 2 O 2 efficiency of up to 74% is obtainable at ∼ 28% phenol conversion to dihydroxybenzenes.

Catalytic properties of titanium silicalites: IV. Vapour phase beckmann rearrangement of cyclohexanone oxime

The transformation of cyclohexanone oxime into caprolactam has been studied over the titnaium silicalite TS-1 and the related MFI analogs, ZSM-5 and Silicalite-1. The incorporation of Ti increases the yield of caprolactam, besides lowering the deactivation rate. Both oxime conversion and selectivity for the lactam increase with increasing Ti content in the zeolite. The influence of temperature and feed rate (WHSV) on the yield of caprolactam over TS-1 has been investigated at different times on stream.

Spectroscopic investigation and catalytic activity of copper(II) phthalocyanine encapsulated in zeolite Y

Copper phthalocyanine (CuPc) encapsulated in zeolite Y was prepared by in situ ligand synthesis method by reacting Cu(II) exchanged NaY with 1,2-dicyanobenzene followed by Soxhlet extraction with several solvents. The encapsulated copper phthalocyanine, CuPcY(e) was characterized by chemical and thermal analyses, FT-IR, diffuse reflectance UV-Vis, and EPR spectroscopic techniques. The spectral studies unequivocally prove the encapsulation of CuPc in the α-cages of zeolite Y and suggest a distortion in the CuPc moiety. The encapsulated materials were more active than neat phthalocyanine in the epoxidation of styrene with tertiary butylhydroperoxide.

Ammoximation of cyclohexanone over a titanium silicate molecular sieve, TS-2

The catalytic activity and selectivity of the titanium silicate molecular sieve, TS-2 (having ZSM-11 structure), in the ammoximation of cyclohexanone and other carbonyl compounds with H2O2 and NH3 is reported in this paper. The studies were carried out at different temperatures and reactant concentrations and with different catalysts. TS-2 produces cyclohexanone oxime with high selectivities, while silicalite-2 and SiO2 produce large quantities of the condensation product, peroxydicyclohexylamine. Similarly, when the concentrations of cyclohexanone and H2O2 are larger than that of NH3, the formation of the byproducts is favoured. Based on the above results, mechanisms for the formation of cyclohexanone oxime and peroxydicyclohexylamine are presented.

Cr-MCM-41-catalyzed selective oxidation of alkylarenes with TBHP

A mild and efficient catalytic method for benzylic oxidation of alkylarenes to the corresponding carbonyl compounds in good yields is described using a catalytic amount of reusable solid, mesoporous chromosilicate (Cr-MCM-41) and 70% tert-butyl hydroperoxide (TBHP) as oxidant.

Hydroisomerization of n-hexane over Pt-SAPO-11 and Pt-SAPO-31 molecular sieves

Abstract SAPO-11 and SAPO-31, two medium pore molecular sieves, were synthesized from aqueous and non-aqueous (ethylene glycol) media. Their acidities (by TPD of pyridine) and their catalytic activities in the isomerization of n-hexane are compared. Samples synthesized from non-aqueous medium possess more acidity and higher activities than those obtained from aqueous medium. 29 Si MAS NMR studies suggest greater substitution of P5+ by Si4+ and lower concentration of silica islands in the samples synthesized from non-aqueous medium. Both SAPO-11 and -31 produce predominantly the monomethyl isomers due to their medium size pores. The activity studies were carried out over Pt-loaded samples in the presence of H2.

Benzylic oxidation with H2O2 catalyzed by Mn complexes of N,N′,N″-trimethyl-1,4,7-triazacyclononane: spectroscopic investigations of the active Mn species

Abstract Mn complexes of N,N′,N″-trimethyl-1,4,7-triazacyclononane (Mn–tmtacn) exhibit good catalytic activity, at ambient temperatures, for the benzylic oxidation of aromatics selectively to the corresponding alcohol and carbonyl compounds with H2O2 as oxidant in the presence of carboxylate buffers. The active Mn species in the reaction medium was investigated by UV–visible (UV–Vis), FT-IR–attenuated total reflectance (FT-IR–ATR) and electron spin resonance (ESR) spectroscopic techniques. The studies revealed the formation of terminal oxo- and μ-oxo-Mn(IV)–tmtacn complexes during the reaction. The oxo-manganese complexes and the nature of the carboxylic acid play an important role in the activation of the benzylic C–H bond.