Karuna Chaudhari

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.

Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation

An EPR study of Ti 3+ in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti 4+ is reduced to Ti 3+ by dry hydrogen above 673 K. Ti ions in TS-1 and TiMCM-41 are located in tetragonally elongated T d and those of ETS-10 and ETS-4 in a tetragonally compressed O h geometric positions. Reduction at 873 K revealed the presence of two non-equivalent Ti 3+ sites in TS-1 and TiMCM-41. Ti 4+ ions in a tetrahedral geometry are more difficult to reduce than in an octahedral symmetry. The effects of cation exchange and Pt impregnation, on the geometry and reducibility of titanium in ETS-10, are also examined. Interaction of a tetrahedrally coordinated Ti 3+ with O 2 or H 2 O 2 results in a diamagnetic titanium(IV) hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti 3+ forms a paramagnetic titanium(IV) superoxo species. The higher catalytic activity of TS-1 and TiMCM-41 in selective oxidation reactions is probably a consequence of the formation of the hydroperoxy species on their surface during the catalytic reaction. The presence of Pt in the vicinity of Ti enables the use of H 2 and O 2 (instead of H 2 O 2 ) to generate the active hydroperoxy site. The absence of formation of titanium hydroperoxy species in ETS-4 and ETS-10 is the cause of their inactivity in selective oxidation reactions.

Immobilization of Cr(salen) moiety in MCM-41 and studies on its catalytic properties

Abstract The [Cr III (salen)] + complex moiety is immobilized in MCM-41 matrix to obtain a new hybrid catalytic system; to test its activity, epoxidation of norbornene and hydroxylation reaction of 1-naphthol are carried out by using TBHP ( tert -butylhydroperoxide) as oxidant.

Vapour phase O‐methylation of 2‐naphthol over the solid bases alkali‐loaded silica and Cs‐loaded MCM‐41

O‐alkylation of 2‐naphthol has been investigated in the vapour phase over alkali‐loaded fumed silica and Cs‐MCM‐41. Both SiO2 and MCM‐41 had low C‐alkylation activities and no O‐alkylation activity. The introduction of alkali ions considerably increases 2‐naphthol conversion with 2‐methoxynaphthalene being the major product. The activity of the catalysts increases with alkali loading and the basicity of the metal (Cs > K > Na > Li). Very high conversion (∼99%) of 2‐naphthol and selectivity (>95%) for 2‐methoxynaphthalene are obtained over Cs‐loaded fumed silica and MCM‐41. A small amount of 1‐methyl‐2‐hydroxynaphthalene is also formed over the Li‐, Na‐ and K‐loaded silica.

Synthesis, characterization and catalytic properties of titanium containing mordenite

Abstract A novel titanium containing zeolite mordenite has been synthesized hydrothermally using 1,4 diaza bicyclo 2,2,2 octane (DABCO) as a templating agent for the first time. Physicochemical characterization of the sample showed that Ti atoms are part of the framework, probably in tetrahedral co-ordination. These zeolites have been found to be active catalysts in phenol hydroxylation with hydrogen peroxide as an oxidant.

Fischer-Tropsch synthesis: effect of water on activity and selectivity for a cobalt catalyst

The addition of water to the syngas (H2O/CO = 0.74) feed for an unsupported cobalt catalyst utilized in a CSTR, where all of the catalyst is exposed to a common feed composition, resulted in an increase in CO conversion. Conversion remains constant during a three-day period, showing that the promotional effect was not of a transitory nature. At the same time the CO hydrogenation increased, the hydrogenation to produce methane decreased as did the secondary hydrogenation of ethene. The addition of higher fractions of H2O/CO led to permanent deactivation of the catalyst for CO conversion but the decrease in hydrogenation to methane and of alkene products remained.

SYNTHESIS AND CATALYTIC PROPERTIES OF MESOPOROUS TIN SILICATE MOLECULAR SIEVES

The synthesis of mesoporous tin-silicates analogous to MCM-41 is reported, for which characterization studies indicate the incorporation of tin in the framework; the Sn-MCM-41 samples have excellent catalytic properties in the selective oxidation of aromatics and hydroxylation of phenol and 1-naphthol with peroxides.

Site preference and reducibility of substituted ferric iron in Fe-ETS-10

Fe-ETS-10 titanosilicates (Si/Fe = 25 and 50) were synthesized and characterized. Based on in situ Mossbauer studies substitution of iron into octahedral sites can be suggested. Upon hydrogen treatment at 670 K temporary stabilization of ferrous state can be detected: this valency change can probably be applied for catalyzing mild oxidation.

n-DBA-VPI-5 : Synthesis and characterization

Abstract Optimization of the synthesis of an ultra-large pore aluminophosphate VPI-5 using di- n-butylamine (n-DBA-VPI-5) has been done. The sample synthesized was characterized by XRD, SEM, FTIR, TGA-DTA, NMR and sorption studies. The extra-large pores (larger than 10) in VPI-5 were confirmed by adsorption measurements. N 2 adsorption at 77K shows mesopores with pore diameter of36 alongwith the micropores of n-DBA-VPI-5.

Synthesis, characterization and catalytic properties of vanadium containing VPI-5

A novel vanadium containing molecular sieve with VPI-5 structure has been synthesized XRD, UV-vis, ESR, NMR and sorption studies suggest that the vanadium ions are in the framework positions. V-VPI-5 is found to be active in the catalytic oxidation of large organic molecules such as 2-methyl naphthalene in the presence of both organic peroxides and H 2 O 2 .