02700nas a2200241   4500008004100000022001400041245009100055210006900146260007300215300001200288490000800300520186300308653000902171653002302180653001902203653001202222653001702234653001702251100002602268700001602294700002602310856012202336       2006                        eng d  a1381-116900aFactors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium0 aFactors influencing decomposition of H2O2 over supported Pd cata  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcDEC  a115-1200 v2603 a<p>Since H2O2 decomposition can result in selectivity/yield loss in the direct H2O2 synthesis process from H-2 and O-2 over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H2O2 decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H2O2 decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 degrees C. This study has shown that the H2O2 decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H2O2 decomposition activity decreased in the following order: hydroiodic acid &gt; hydrobromic acid &gt; hydrochloric acid &gt;&gt; acetic acid &gt; phosphoric acid &gt; sulfuric acid &gt; perchloric acid. The ability of the acid to decrease the H2O2 decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H2O2 decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H2O2 decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H2O2 decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H2O2. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H2O2 decomposition activity. (c) 2006 Elsevier B.V. All rights reserved.</p>10aacid10aH2O2 decomposition10aH2O2 synthesis10ahalides10aPd catalysts10apretreatment1 aChoudhary, Vasant, R.1 aSamanta, C.1 aChoudhary, Tushar, V.  uhttps://library.ncl.res.in/content/factors-influencing-decomposition-h2o2-over-supported-pd-catalyst-aqueous-medium-001322nas a2200253   4500008004100000022001400041245017700055210006900232260009500301300001000396490000800406520026600414653003600680653002300716653002300739653005100762653002700813100002100840700001900861700001900880700002500899700002300924856012100947       2006                        eng d  a0021-951700aRemarkably rapid regioselective synthesis of beta-enaminones using silica chloride in a heterogeneous as well as an ionic liquid in a homogeneous medium at room temperature0 aRemarkably rapid regioselective synthesis of betaenaminones usin  a525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USAbACADEMIC PRESS INC ELSEVIER SCIENCEcFEB  a37-460 v2453 a<p>{Silica chloride as a heterogeneous catalyst has been used for the regioselective synthesis of P-amino-a,P unsaturated esters and ketones. Similar regioselective synthesis was also performed using an ionic liquid 1-n-butyl imidazolium tetrafluoroborate [</p>10adirect oxidation of H-2 to H2O210aH2O2 decomposition10aH2O2 hydrogenation10aPromoting action of chloride or bromide anions10asupported Pd catalysts1 aGholap, Atul, R.1 aChakor, N., S.1 aDaniel, Thomas1 aLahoti, Rajgopal, J.1 aSrinivasan, K., V.  uhttps://library.ncl.res.in/content/remarkably-rapid-regioselective-synthesis-beta-enaminones-using-silica-chloride-102189nas a2200205   4500008004100000022001400041245016800055210006900223260007300292300001400365490000600379520132800385653002601713653002601739653002301765653002101788100002201809700002601831856012601857       2007                        eng d  a1566-736700aDirect formation of H2O2 from H-2 and O-2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system0 aDirect formation of H2O2 from H2 and O2 and decompositionhydroge  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcDEC  a2222-22280 v83 a<p>Formation of H2O2 from H-2 and O-2 and decomposition/hydrogenation of H2O2 have been studied in aqueous acidic medium over Pd/SiO2 catalyst in presence of different halide ions (viz. F-, Cl- and Br-). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H2O2 formation selectivity in the H-2 to H2O2 oxidation over the catalyst. The H2O2 destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br- was found to selectivity promote the conversion of H-2 to H2O2 by significantly reducing the H2O2 decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H2O2 formation by promoting the H-2 combustion to water and/or by increasing the rate of decomposition/hydrogenation of H2O2 over the catalyst. An optimum concentration of Br- ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H2O2, yield in the direct synthesis. (c) 2007 Elsevier B.V. All rights reserved.</p>10aBr- catalyst promoter10adirect H2O2 formation10aH2O2 decomposition10aPd/SiO2 catalyst1 aSamanta, Chanchal1 aChoudhary, Vasant, R.  uhttps://library.ncl.res.in/content/direct-formation-h2o2-h-2-and-o-2-and-decompositionhydrogenation-h2o2-aqueous-acidic-002367nas 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<p>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.</p>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<p>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.</p>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-003284nas a2200241   4500008004100000022001400041245018000055210006900235260007300304300001200377490000800389520231000397653002302707653002302730653002702753653002202780653002902802653001802831100002602849700002202875700001802897856012702915       2007                        eng d  a0926-860X00aFormation from direct oxidation of H-2 and destruction by decomposition/hydrogenation of H2O2 over Pd/C catalyst in aqueous medium containing different acids and halide anions0 aFormation from direct oxidation of H2 and destruction by decompo  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcFEB  a234-2430 v3173 a<p>Direct oxidation of H-2 by O-2 to H2O2 and decomposition/hydrogenation of H2O2 (at 27 degrees C and atmospheric pressure) over Pd/C catalyst in an aqueous acidic reaction medium have been thoroughly investigated using different mineral acids (viz. 0.1 N H2SO4, H3PO4, H3BO3, HNO3, HCl, HBr or HI) and/or halide anions (viz. F-, Cl-, Br- or I-), covering their wide concentration range (0-24 mmol/dm(3)), in the reaction medium. In the absence of any externally added halide, appreciable H2O2 formation in the H2 oxidation occurred only when the medium contained HCl. However, the rates of H2O2 decomposition and hydrogenation are greatly reduced because of the presence of any acid; the influence on the H2O2 decomposition was, however, much larger for the halo acids. In the presence of acid (0.1 N H3PO4 or H2SO4), the H-2-to-H2O2 formation reaction is greatly enhanced by the externally added halide anions up to their optimum concentrations. However, above the optimum halide anion concentration, it is inhibited more than the H-2-to-water formation (parallel) reaction, causing a decrease in both the H2O2 yield and selectivity. Whereas, the H-2 conversion and H2O2 destruction activities of the catalyst are decreased continuously with increasing the halide anion (except F-) concentration. Among the halides, chloride is the best halide promoter for Pd/C catalyst in the H-2-to-H2O2 oxidation. At the optimum Cl-concentration (5.4 mmol/dm(3)), both the H-2 conversion and H2O2 yield are passed through a maximum and the H2O2 decomposition is greatly inhibited with increasing the phosphoric acid concentration. In the absence of either the chloride anions or the acid (or both) in the reaction medium, only a little or no H2O2 is formed in the H-2 oxidation and also the rate of H2O2 destruction is very fast, particularly in the presence of H-2; the rapid destruction of H2O2 is mainly due to its decomposition rather than its hydrogenation. The best H-2-to-H2O2 oxidation results are obtained at the optimum concentrations of both the acid and halide anions. In the presence of acid and chloride (or bromide) promoter, the H2O2 hydrogenation dominates the H2O2 destruction and hence the net H2O2 formation is mainly controlled by the H2O2 hydrogenation. (c) 2006 Published by Elsevier B.V.</p>10aH2O2 decomposition10aH2O2 hydrogenation10ahalide anion promoters10aHydrogen peroxide10aoxidation of H-2-to-H2O210aPd/C catalyst1 aChoudhary, Vasant, R.1 aSamanta, Chanchal1 aJana, Prabhas  uhttps://library.ncl.res.in/content/formation-direct-oxidation-h-2-and-destruction-decompositionhydrogenation-h2o2-over-pdc02138nas a2200217   4500008004100000022001400041245010900055210006900164260006900233300001200302490000800314520131400322653001301636653002601649653002301675653002301698653002101721100002201742700002601764856013001790       2008                        eng d  a1385-894700aDirect oxidation of H-2 to H2O2 over Pd/CeO2 catalyst under ambient conditions: influence of halide ions0 aDirect oxidation of H2 to H2O2 over PdCeO2 catalyst under ambien  aPO BOX 564, 1001 LAUSANNE, SWITZERLANDbELSEVIER SCIENCE SAcMAR  a126-1320 v1363 a<p>Direct oxidation of H-2 by O-2 to H2O2 and decomposition/hydrogenation of H2O2 have been investigated over Pd/CeO2 catalyst in presence of different halide ions. All reactions were carried out in an aqueous acidic (0.03 M H3PO4) medium at room temperature (25 degrees C) and atmospheric pressure. When different halide ions were added directly to the reaction medium or incorporated in the catalyst, the activity/selectivity of Pd/CeO2 catalyst in the H-2 to H2O2 oxidation changed significantly, depending upon the nature of the halide ions. Different ammonium halides impregnated reduced Pd/CeO2 catalyst calcined under inert (flowing nitrogen) and oxidizing (static/flowing air) gaseous atmospheres revealed that bulk oxidation state of Pd and the nature of the halide ions incorporated into the catalyst cooperatively control the activity/selectivity of catalyst in H-2 to H2O2 oxidation. Both H2O2 decomposition and hydrogenation were found to affect strongly depending upon the nature of the halide ions present in the reaction medium or in the catalyst. Among the different halides, bromide was found the most effective promoter for enhancing the H2O2 yield/selectivity in H-2 to H2O2 oxidation, irrespective of the Pd oxidation state in the catalyst. (c) 2007 Elsevier B.V. All rights reserved.</p>10aBr- ions10aH-2 to H2O2 oxidation10aH2O2 decomposition10aH2O2 hydrogenation10aPd/CeO2 catalyst1 aSamanta, Chanchal1 aChoudhary, Vasant, R.  uhttps://library.ncl.res.in/content/direct-oxidation-h-2-h2o2-over-pdceo2-catalyst-under-ambient-conditions-influence-halide-002497nas a2200217   4500008004100000022001400041245016500055210006900220260007300289300001000362490000800372520160500380653002701985653002302012653002302035653002302058653002202081100002602103700001802129856013202147       2009                        eng d  a0926-860X00aDirect H-2-to-H2O2 oxidation over highly active/selective Br-F-Pd/Al2O3 catalyst in aqueous acidic medium: Influence of process conditions on the H2O2 formation0 aDirect H2toH2O2 oxidation over highly activeselective BrFPdAl2O3  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcJAN  a35-420 v3523 a<p>The influence of the O-2/H-2 mote ratio in the gaseous feed and also those of other reaction conditions [viz. concentration of H3PO4 (0-5 mol/dm(3)). temperature (5-50 degrees C, gas (H-2 and O-2) space velocity (5.8-23.4 h(-1)) and reaction time (0.1-8 h)] on the H2O2 formation in the H-2-to-H2O2 oxidation over the Br(1 wt%)-F(1 wt%)-Pd(5 wt%)/Al2O3 catalyst in an aqueous acidic (H3PO4) medium have been thoroughly investigated. The effects of the O-2/H-2 ratio, reaction temperature and acid concentration on the destruction of H2O2 by its decomposition and/or hydrogenation reactions over the catalyst in the acidic reaction medium have also been studied. The net H2O2 formation (H2O2 yield) over the catalyst passed through a maximum with increasing the acid concentration, the temperature or the O-2/H-2 feed ratio. However, it decreased markedly with increasing the gas space velocity or the reaction period. The H2O2 decomposition and hydrogenation activities of the catalyst increased appreciably with increasing the reaction temperature and decreased with increasing the acid concentration. The H2O2 destruction during the H-2-to-H2O2 oxidation increased with increasing the concentration of H-2 (relative to that of O-2) due to the increased H2O2 hydrogenation rate over the catalyst. The net H2O2 formation in the H-2-to-H2O2 oxidation decreased sharply with increasing the initial amount of H2O2 present in the reaction mixture. The presence of H2O2 and the higher H-2/O-2 ratios have detrimental effects on the net formation of H2O2. (C) 2008 Elsevier B.V. All rights reserved.</p>10aBr-F-Pd/Al2O3 catalyst10aH2O2 decomposition10aH2O2 hydrogenation10ahydrogen oxidation10aHydrogen peroxide1 aChoudhary, Vasant, R.1 aJana, Prabhas  uhttps://library.ncl.res.in/content/direct-h-2-h2o2-oxidation-over-highly-activeselective-br-f-pdal2o3-catalyst-aqueous-acidic-0