Drastic increase of selectivity for H2O2 formation in direct oxidation of H2 to H2O2 over supported Pd catalysts due to their bromination

Choudhary, Vasant R.; Samanta, Chanchal; Gaikwad, A. G.

doi:10.1039/b405415f

Cited by 63 publications

(50 citation statements)

References 7 publications

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“…The increase of the concentration of Br -anions significantly decrease the rate of H 2 O 2 conversion, in agreement with literature results [4,27,36,40]. The exponential-type decrease of the rate constant on increasing Br ) concentration is more consistent with the indication that Br ) on the surface may block the sites for the dissociation of O 2 [36,40] rather that the interaction of bromide anions with palladium change its electronic properties [27], because in the latter case a linear or volcano-type dependence should be expected.…”

Section: Decomposition Versus Reductive Pathway In H 2 O 2 Conversionsupporting

confidence: 82%

“…The exponential-type decrease of the rate constant on increasing Br ) concentration is more consistent with the indication that Br ) on the surface may block the sites for the dissociation of O 2 [36,40] rather that the interaction of bromide anions with palladium change its electronic properties [27], because in the latter case a linear or volcano-type dependence should be expected. Alternative explanation is that Br ) anions, which can acts as electron scavenger, will inhibit radical-type decomposition pathways [5].…”

Section: Decomposition Versus Reductive Pathway In H 2 O 2 Conversionsupporting

confidence: 61%

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The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

et al. 2006

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The kinetic behavior in the direct synthesis of H 2 O 2 with Pd-Me (Me = Ag, Pt) catalysts prepared by depositing the noble metals by electroless plating deposition (EPD) or deposition-precipitation (DP) methods on a-Al 2 O 3 asymmetric ceramic membrane with or without a further surface coating by a carbon thin layer is reported. The effect of the second metal with respect to Pd-only catalysts considerably depends on the presence of the carbon layer on the membrane support. Several factors in the preparation of these membranes as well as the reaction conditions (temperature, concentration of Br ) , pH) determine the selectivity in H 2 O 2 formation, influencing the rate of the consecutive reduction of H 2 O 2 (which is faster with respect to H 2 O 2 decomposition on the metal surface) and/or of direct H 2 + O 2 conversion to H 2 O. Defective Pd sites are indicated to be responsible for the two unselective reactions leading to water formation (parallel and consecutive to H 2 O 2 formation), but the rate constants of the two reactions are differently influenced from the catalytic membrane characteristics. Increasing the noble metal loading on the membrane not only increases the productivity to H 2 O 2 , but also the selectivity, due to the formation of larger, less defective, Pd particles.

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Section: Decomposition Versus Reductive Pathway In H 2 O 2 Conversionsupporting

confidence: 82%

Section: Decomposition Versus Reductive Pathway In H 2 O 2 Conversionsupporting

confidence: 61%

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

et al. 2006

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“…In particular, the influence of the addition of the halides and acids was studied on a macroscopic level as recently reported 27,28 . For instance, Choudhary et al 27 studied the impregnation of bromide on a 5% Pd/Al 2 O 3 catalyst and found an optimum, in terms of the catalyst activity/selectivity.…”

Section: Introductionmentioning

confidence: 98%

“…For instance, Choudhary et al 27 studied the impregnation of bromide on a 5% Pd/Al 2 O 3 catalyst and found an optimum, in terms of the catalyst activity/selectivity. More or less, it was found to be equal to 0.42 Br-to-Pd molar ratio.…”

Section: Introductionmentioning

confidence: 98%

Revealing the role of bromide in the H₂O₂ direct synthesis with the catalyst wet pretreatment method (CWPM)

et al. 2016

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A tailor-made Pd 0 /K2621 catalyst was subjected to post synthesis modification via a wet treatment procedure. The aim was the understanding of the role of promoters and how -if any -improvements could be qualitatively related to the catalyst performance for the H 2 O 2 direct synthesis. The Catalyst Wet Pretreatment Method (CWPM) was applied in different methanolic solutions containing H 2 O 2 , NaBr and H 3 PO 4 , either as single modifiers or as a mixture. The catalyst was characterized by Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). It was concluded that the modified catalysts give rise to higher selectivities compared to the pristine reference catalyst thus opening a possibility to exclude the addition of the undesirable selectivity enhancers in the reaction medium. This work provides original evidence on the role of promoters, especially bromide, allowing the formulation of a new reaction mechanism for one of the most ISCRE 24 -Foundations and

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“…For a catalyst to be viable for the direct synthesis reaction, it must exhibit high H 2 selectivity towards H 2 O 2 , and if the H 2 O 2 produced during the direct synthesis process is to be subsequently used as an oxidant, the H 2 O 2 solution must be free of the halide and acid additives that Pd catalysts typically require in the reaction medium in order to achieve adequate activity and selectivity [4][5][6][7][8][9][10]. The addition of Au into Pd catalysts was shown to provide materials that were extremely active for the direct synthesis process [11][12][13] and yet still worked well in the absence of any acid and halide stabilisers.…”

Section: Introductionmentioning

confidence: 99%

The effect of heat treatment on the performance and structure of carbon-supported Au–Pd catalysts for the direct synthesis of hydrogen peroxide

Edwards

Pritchard

Piccinini

et al. 2012

Journal of Catalysis

101

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a b s t r a c tThe direct synthesis of hydrogen peroxide using supported gold palladium catalysts prepared by incipient wetness impregnation is described and discussed. The effect of an acid pre-treatment step on the activated carbon support prior to the deposition of the metals, together with the effect of the calcination temperature, has been investigated. The acid pre-treated samples all show superior activity to those materials prepared with the omission of this acid pre-treatment stage. The calcination temperature affects both the re-usability and hydrogenation activity of the catalysts. Detailed characterisation using X-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy is described. The enhanced activity is associated with a higher surface concentration of palladium in the acid pre-treated samples which is principally present as Pd 2+ . Calcination of the catalysts at 400°C is required to achieve re-usable and stable catalysts, and this is associated with the morphology and dispersion of the metal nanoparticles. The surface ratio of Pd 0 /Pd 2+ is found to be an important factor controlling the hydrogenation of hydrogen peroxide, and a series of controlled reduction and re-oxidation of a sample show how the Pd 0 /Pd 2+ surface ratio can influence the relative rates of hydrogen peroxide synthesis and hydrogenation.

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Drastic increase of selectivity for H2O2 formation in direct oxidation of H2 to H2O2 over supported Pd catalysts due to their bromination

Cited by 63 publications

References 7 publications

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

Revealing the role of bromide in the H₂O₂ direct synthesis with the catalyst wet pretreatment method (CWPM)

The effect of heat treatment on the performance and structure of carbon-supported Au–Pd catalysts for the direct synthesis of hydrogen peroxide

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Drastic increase of selectivity for H2O2 formation in direct oxidation of H2 to H2O2 over supported Pd catalysts due to their bromination

Cited by 63 publications

References 7 publications

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

Revealing the role of bromide in the H2O2 direct synthesis with the catalyst wet pretreatment method (CWPM)

The effect of heat treatment on the performance and structure of carbon-supported Au–Pd catalysts for the direct synthesis of hydrogen peroxide

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Revealing the role of bromide in the H₂O₂ direct synthesis with the catalyst wet pretreatment method (CWPM)