02461nas a2200205   4500008004100000022001400041245025900055210006900314260007300383300001000456490000800466520149200474653003101966653002201997653002902019653003402048100002602082700001802108856012902126       2007                        eng d  a0926-860X00aDirect oxidation of H-2 to H2O2 over Br and F-promoted Pd/Al2O3 in aqueous acidic medium: influence of the concentration of Br and F and the method of incorporation of the two halogens in the catalyst on their beneficial synergetic effect on the net H2O20 aDirect oxidation of H2 to H2O2 over Br and Fpromoted PdAl2O3 in   aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcOCT  a79-850 v3293 a<p>Influence of the addition of F (0-1.1 mmol/g) in the pre-brominated Pd/Al2O3 (Br loading = 0.13 mmol/g) and also that of Br (0.13 mmol/g) in the pre-fluorinated Pd/Al2O3 (F loading = 0.53 mmol/g) on the net H2O2 formation in the H-2-to-H2O2 oxidation (with H-2/O-2 mole ratio of 1.0) over the halogenated catalysts in aqueous acidic (0.1 M H3PO4) medium have been investigated. In both the cases, the highest synergetic effect (resulting in the highest net H2O2 formation) produced by the addition of other halogen is observed at its optimum concentration (viz. 0.13 mmol Br/g in the fluorinated Pd/Al2O3 and 0.13 mmol F/g in the pre-brominated Pd/Al2O3). The beneficial synergetic effect of the two halogens is also found to be strongly influenced by the way of incorporation of the two halogens in the catalyst. The enhancement in the net rate of H2O2 formation due to the synergetic effect for the different methods of Pd/Al2O3 halogenation is in the following order: simultaneous bromination and fluorination &lt; first fluorination and then bromination &lt; first bromination and then fluorination. The fluorination (at optimum concentration of 0.13 mmol F/g) of the pre-brominated (0.13 mmol Br/g) Pd/Al2O3 led to the best catalyst for the H-2-to-H2O2 oxidation with 100% H-2 conversion and 78% H2O2 yield/selectivity. The destruction of H2O2 by its decomposition and/or hydrogenation over the halogenated catalysts has also been studied. (c) 2007 Published by Elsevier B.V.</p>10aF and Br-promoted Pd/Al2O310aHydrogen peroxide10aoxidation of H-2-to-H2O210asynergetic effect of F and Br1 aChoudhary, Vasant, R.1 aJana, Prabhas  uhttp://library.ncl.res.in/content/direct-oxidation-h-2-h2o2-over-br-and-f-promoted-pdal2o3-aqueous-acidic-medium-influence-003283nas a2200241   4500008004100000022001400041245018000055210006900235260007300304300001200377490000800389520231000397653002302707653002302730653002702753653002202780653002902802653001802831100002602849700002202875700001802897856012602915       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  uhttp://library.ncl.res.in/content/formation-direct-oxidation-h-2-and-destruction-decompositionhydrogenation-h2o2-over-pdc