Chemo-, regio- and stereo-selective aerial oxidation of limonene to the endo-1,2-epoxide over Mn(Salen)-sulfonated SBA-15

Mn(Salen) complexes immobilized on sulfonic acid-functionalized SBA-15 molecular sieves (SBA-15-pr-SO3-Mn(Salen)) catalyze the Mukaiyama-type oxidation of R-(+)-limonene selectively to the 1,2-epoxide with molecular oxygen at 298 K (Salen=N,N-ethylenebis(salicylidenaminato)). The endo-diastereomer is formed with a diasteromeric excess of 39.8%. This catalyst exhibited higher catalytic activity than "neat" Mn(Salen) complexes directly supported on SBA-15 or zeolite-Y. A change in the oxidation state of Mn from +3 in the "neat" complex to +2 when immobilized on the sulfonated surface is a probable cause for the observed enhancement of catalytic activity. A part of the Mn complexes was leached out of the solid phase during the reaction

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

An EPR study of Ti3+ in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti4+ is reduced to Ti3+ by dry hydrogen above 673 K. Ti ions in TS-1 and TiMCM-41 are located in tetragonally elongated Td and those of ETS-10 and ETS-4 in a tetragonally compressed Oh geometric positions. Reduction at 873 K revealed the presence of two non-equivalent Ti3+ sites in TS-1 and TiMCM-41. Ti4+ 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 Ti3+ with O2 or H2O2 results in a diamagnetic titanium(IV) hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti3+ 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 H2 and O2 (instead of H2O2) 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

Zeolite-encapsulated manganese(III)salen complexes

Manganese(III) complexes of [N,N'-ethylenebis(salicylidene-aminato)] (salen), [N,N'-ethylenebis(5-chloro-salicylidene-aminato)] (Cl<SUB>2</SUB>Salen), [N,N'-ethylenebis(5-bromo-salicylidene-aminato)] (Br<SUB>2</SUB>Salen) and [N,N'-ethylenebis(5-nitro-salicylidene-aminato)] [(NO<SUB>2</SUB>)<SUB>2</SUB>Salen] have been encapsulated in the supercages of zeolite X by the zeolite synthesis method. The catalysts have been characterized by FTIR, UV-Vis and EPR spectroscopic techniques, XRD, SEM, thermal and elemental analysis, as well as nitrogen adsorption and cyclic voltammetric studies. The extent of encapsulation of the Mn(III)Salen complexes in zeolite X varies with the nature of the substituent group on the aromatic ring. While bromo groups enhance encapsulation, substitution with -NO<SUB>2</SUB> groups decreases the amounts of Mn(III) complexes encapsulated in the cavities of the zeolites. Cyclic voltammetric data indicate that the zeolite matrix facilitates the reduction of Mn(III) to Mn(II), suggesting that it behaves like an electron-withdrawing substituent. The aerobic oxidation of styrene to benzaldehyde, styrene oxide and phenylacetaldehyde over these catalysts is also reported

An Experiment in Deploying Next Generation Network Protocols

This paper presents IP(dmux) - a network-layer infrastructure that serves as a general-purpose deployment vehicle for next-generation network protocols. For each new network protocol, IP(dmux) provides a network-level access path between any end-user and the (approximately) closest router supporting the new protocol. IP(dmux) thus ensures that even partial deployments of new protocols are easily accessible by the global Internet user population. We present the design and implemention of IP(dmux) which we then use to experiment with three next-generation IP architectures - IPv6, FRM (a new protocol for global network-layer multicast) and i3 (a rendezvous-based network architecture). Our experiences suggest new networklayer architectures can easily leverage IP(dmux) to aid their deployment. Moreover, our evaluation through simulation, measurement and wide-area deployment indicates that even small-sized IP(dmux) deployments can yield reasonable endto- end performance for partially deployed next generation architectures

Isomorphous substitution of iron in the framework of zeolite ZSM-23

A crystalline ferrisilicate having the framework structure of ZSM-23 zeolite has been synthesized and characterized. The presence of iron in the zeolite lattice framework has been confirmed by spectroscopic (XRD, framework IR, ESR, and XPS), DTA/TG, magnetic susceptibility, ion exchange, and catalytic activity results. Chemical analysis and XPS show the absence of any significant quantity of Al(SiO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB> &gt; 1400) in the ferrisilicate. XRD patterns of the as-synthesized as well as the calcined Fe/ZSM-23 matched well with that of ZSM-23 (MTT topology). Framework IR bands of ZSM-23 are shifted toward lower frequencies on incorporation of iron in the framework. The white color of the as-synthesized as well as that of calcined samples of Fe/ZSM-23, ESR (g=4.4), and magnetic susceptibility (&#956;=5.4-5.8, BM) data indicate that Fe-O-Fe interactions (due to oxides of iron like Fe<SUB>2</SUB>O<SUB>3</SUB> or Fe<SUB>3</SUB>O<SUB>4</SUB>) are absent, and that well dispersed Fe 31 ions are present in a magnetically dilute environment. Fe/ZSM-23 exhibits significant ion exchange capacity and catalytic activity/shape selectivity in the metaxylene isomerization reaction. Fe<SUP>2+</SUP> ions in zeolite lattice positions account for the ion exchange capacity and shape selective catalytic activity of this crystalline ferrisilicate

Transition metal-silicate analogs of zeolites

The synthesis and characterization of three transition metal (Fe3+, Ti4+ and V4+)-silicate molecular sieves are discussed. The key factors for a successful incorporation of these metal ions in the growing silicate network during gel preparation/hydrothermal synthesis (e.g. avoidance of insoluble/sparingly soluble metal hydroxides/oxyhydroxides (Fe3+ and Ti4+) and alkali metal ions (Ti4+ and V4+/5+)) as well as the effects of post synthesis drying, calcination etc. on the stability of these metal ions in the framework are evaluated. Various spectroscopic and other techniques which are required to provide general as well as specific structural and textural information about the fate of these transition metal ions are discussed

Acidic and catalytic properties of the Ca-Pt-H-mordenite system

The acid strength distribution and catalytic behavior (activity, selectivity, and deactivation in the reactions of ortho-xylene) of H-mordenite (HM), calcium mordenite (CaM), platinum H-mordenite (PtHM), calcium platinum H-mordenite (CaPtHM) and calcium platinum H-dealuminated-mor-denite (DCaPtHM) have been studied. Measurement of the isosteric heats of adsorption of NH3 indicate that the concentration of strong acid sites in these catalysts follow the order: HM &gt; DCaPtHM &gt; CaPtHM &gt; PtHM &gt; CaM. Their initial activity for the conversion of ortho-xylene decreases as HM &gt; DCaPtHM &gt; PtHM &gt; CaPtHM &gt; CaM. The selectivity of these catalysts in yielding isomeric xylenes rather than non-C8 aromatics by disproportionation reaction decreases in the following order: CaM &gt; DCaPtHM &gt; HM &gt; CaPtHM &gt; PtHM. The catalyst undergo deactivation due to coke formation in the following order: HM &gt; DCaPtHM &gt; CaPtHM &gt; PtHM=CaM. An attempt is made to correlate the observed catalytic behavior with the acidic and steric features of the catalysts

Selective oxidations over zeolite- and mesoporous silica-based catalysts: selected examples

Selective oxidation of hydrocarbons/terpenes in the liquid phase are reported over three categories of zeolite- and mesoporous silica-based catalysts: (1) transition metal complexes (metal phthalocyanines, copper acetate dimers and Co/Mn acetate trimer) encapsulated in zeolite-Y, (2) transition metal complexes (Mn-Salen), grafted on SBA-15, and (3) transition metal ions in framework positions of zeolites and mesoporous molecular sieves like Ti-silicates. Upon heterogenization, the metal complexes exhibited enhanced catalytic acitivity/selectivity. The causes for the enhanced catalytic activity/product selectivity have been explored. Dimer formation (copper acetate) or geometric distortion in the zeolite cavities (metal phthalocyanines) and consequent changes in energy levels and redox potentials are shown to modify the catalytic activity (in the selective oxidation of hydrocarbons) of the encapsulated metal complexes. In the case of Mn-Salen grafted on SBA-15, increasing the acidity of the siliceous surface (by -SO3H groups, for example) leads to a more facile reduction of the Mn ions and, thereby, enhanced catalytic activity in the selective epoxidation of limonene. When Ti ions are introduced in framework positions, reactive metal-oxo species are formed on contact with H2O2 or O2, which influence the mode of O-O cleavage (heterolytic/homolytic) and product selectivity. The structure–function relationships in these catalysts are reported