02367nas a2200217 4500008004100000022001400041245018500055210006900240260007300309300001000382490000600392520143600398653002601834653003001860653002301890653002301913653003701936100002201973700002601995856012802021 2007 eng d a1566-736700aDirect synthesis of H2O2 from H-2 and O-2 over Pd/H-beta catalyst in an aqueous acidic medium: influence of halide ions present in the catalyst or reaction medium on H2O2 formation0 aDirect synthesis of H2O2 from H2 and O2 over PdHbeta catalyst in aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcJAN a73-790 v83 a

The influence of different halide ions present in the catalyst or reaction medium on the performance of Pd/H-beta catalyst in the direct H2O2 synthesis in an aqueous acidic (0.03 M H3PO4) reaction medium at 27 degrees C and atmospheric pressure has been thoroughly investigated. The results showed a strong influence of both the bulk Pd oxidation state in the catalyst and the halide ions added to the reaction medium on the performance of the catalyst in the H-2 to H2O2 oxidation, H2O2 decomposition/hydrogenation reactions. The different ammonium halides impregnated reduced Pd/H-beta catalyst calcined in inert (N-2) and oxidizing (air) gaseous atmospheres also revealed that the bulk Pd oxidation state and nature of the halide ions present in the catalyst together control the overall performance of the catalyst in the H2O2 formation reaction. The presence of halide ions in reaction medium or in the catalyst significantly changes the selectivity for H2O2 formation in the direct H2O2 synthesis. Bromide ions are found to remarkably enhance the H2O2 selectivity in the direct H2O2 synthesis irrespective of the Pd oxidation state in the catalyst. The promoting action of Br- is attributed mainly to the large decrease in the H2O2 decomposition and hydrogenation activities of the catalyst and also inhibition for the non-selective H-2-to-water oxidation over the catalyst. (c) 2006 Elsevier B.V. All rights reserved.

10adirect H2O2 synthesis10aH-P supported Pd catalyst10aH2O2 decomposition10aH2O2 hydrogenation10apromoting action of bromide ions1 aSamanta, Chanchal1 aChoudhary, Vasant, R. uhttps://library.ncl.res.in/content/direct-synthesis-h2o2-h-2-and-o-2-over-pdh-beta-catalyst-aqueous-acidic-medium-influence02755nas a2200217 4500008004100000022001400041245015600055210006900211260007300280300001000353490000800363520186800371653002602239653002302265653002302288653002402311653002302335100002202358700002602380856013102406 2007 eng d a0926-860X00aDirect synthesis of H2O2 from H-2 andO(2) and decomposition/hydrogenation of H2O2 in an aqueous acidic medium over halide-modified Pd/Al(2)O3 catalysts0 aDirect synthesis of H2O2 from H2 andO2 and decompositionhydrogen aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcOCT a23-320 v3303 a

Direct synthesis Of H2O2 from its elements was carried out in an acidic aqueous reaction medium over halide-modified oxidized and reduced Pd/ Al2O3 catalysts under very mild conditions (at 27 degrees C and atmospheric pressure). The halide ions were introduced into the catalyst by incorporating halide ions into supported Pd/gamma-Al2O3 catalyst or via depositing halide ions on the support (gamma-Al2O3) prior to Pd deposition. The H2O2 decomposition and hydrogenation over the corresponding catalysts were also carried out under the reaction conditions similar to those employed for the H2O2 synthesis in order to elucidate the factors strongly affecting the H2O2 yield/selectivity in the direct H2O2 process. The performance of halide-modified Pd/Al2O3 catalysts in the direct H2O2 synthesis revealed that halide insertion in the catalyst system prior to or after Pd deposition on the support had comparable qualitative effect on the H2O2 formation. Both the Pd oxidation state and the nature of the halide ions had strong influences on the H-2 conversion (in direct H2O2 Synthesis process) and H2O2 decomposition and/or hydrogenation reaction. While the effect of Pd oxidation state on the H2O2 formation was significant for the catalytic system containing F- and Cl- ions, the influence of the Pd oxidation state was found less important for the catalyst system containing Br- ions; the H2O2 formation selectivity increased significantly due to the presence of Br- ions, irrespective of the Pd oxidation state. The nature of the H2O2 destruction pathway (i.e. hydrogenation and/or decomposition) in the presence of hydrogen over halide-modified Pd/Al2O3 catalysts was found to be strongly dependent upon the nature of the halide ions incorporated in the catalyst during halide-modification of the catalyst. (C) 2007 Elsevier B.V. All rights reserved.

10adirect H2O2 synthesis10aH2O2 decomposition10aH2O2 hydrogenation10ahalide-modification10aPd oxidation state1 aSamanta, Chanchal1 aChoudhary, Vasant, R. uhttps://library.ncl.res.in/content/direct-synthesis-h2o2-h-2-ando2-and-decompositionhydrogenation-h2o2-aqueous-acidic-medium-000820nas a2200217 4500008004100000022001400041245008900055210006900144260007300213300001400286490000600300520003200306653001800338653002600356653001200382653001300394100002300407700002500430700002900455856011800484 2007 eng d a1566-736700aTethered Pd-complex on solid support: catalyst for acid-free carbonylation reactions0 aTethered Pdcomplex on solid support catalyst for acidfree carbon aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcSEP a1386-13920 v83 a

{Palladium complex [

10adecomposition10adirect H2O2 synthesis10ahalides10aPromoter1 aSarkar, Bibbas, R.1 aMukhopadhyay, Kausik1 aChaudhari, Raghunath, V. uhttps://library.ncl.res.in/content/tethered-pd-complex-solid-support-catalyst-acid-free-carbonylation-reactions-0