DFT calculations on selectivity enhancement by Br addition on Pd catalysts in the direct synthesis of hydrogen peroxide

Lee, Min Woo; Jo, Deok Yeon; Han, Geun-Ho; Lee, Kwan‐Young

doi:10.1016/j.cattod.2021.09.030

Cited by 7 publications

(4 citation statements)

References 48 publications

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“…H 2 O and O 2 reactant species were expected to adsorb molecularly and form H 2 O* and O 2 *, and O* was expected to form through O 2 * dissociation. Activated hydroxyl (OH*, Figure d) has been considered as the final intermediate in the H 2 O 2 formation. − Adsorbed OH species will not desorb directly as gas phase OH radicals due to the considerable energy requirements. Another intermediate during the direct formation of hydrogen peroxide is a hydroperoxyl (OOH*) species (Figure e).…”

Section: Resultsmentioning

confidence: 99%

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Wei,

Movick,

Obata

et al. 2024

J. Phys. Chem. C

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There has been an increase in demand worldwide for efficient use of natural gas. Thus, studies have been investigating the oxidative coupling of methane (OCM) to higher hydrocarbons, which can directly form a C−C bond in a single reactor at high temperatures. However, the OCM reaction still has a drawback of low product selectivity due to overoxidation of the C 2 products. Among the OCM catalysts investigated, alkali-based catalysts, especially Na 2 WO 4 and K 2 WO 4 , have demonstrated a high C 2 yield via a unique response to H 2 O, one of the dominant products of the OCM reaction. It was postulated that the catalyst forms highly reactive OH radicals from O 2 and H 2 O, which is responsible for its high selectivity and conversion rate. Previous studies with near-ambient-pressure X-ray photoelectron spectroscopy suggested the involvement of alkali (su)peroxide formation. Based on this, density functional theory calculation was applied to examine an unmolten K 2 WO 4 surface (in contrast to molten Na 2 WO 4 ). To construct the crystal structure for calculation, in situ Xray diffraction measurement was used, which provided the crystal phase of hexagonal K 2 WO 4 at temperatures relevant to OCM. This phase resulted from the transformation of monoclinic K 2 WO 4 under ambient conditions. Generally, a stable surface was found to occur with K atoms on the outer surface rather than with the O-or W-exposed surfaces. After considering various intermediates with different positions, a plausible surface pathway that leads to H 2 O 2 through adsorptions of H 2 O and O 2 was suggested. The calculation results support the hypothesis of the involvement of OH radicals in the OCM through a unique water-activation pathway.

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Section: Resultsmentioning

confidence: 99%

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Wei,

Movick,

Obata

et al. 2024

J. Phys. Chem. C

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“…Regarding the H 2 O 2 decomposition reaction, it seems that the presence of Br − or Cl − highly inhibits the decomposition rate of H 2 O 2 to H 2 O. Too high concentrations of halide ions can cause the leaching of active metals and also deactivate the catalysts by adsorption on the active species [109]. The utilization of halide ions was also studied by incorporating them onto the catalyst surface.…”

Section: In Situ Generated H 2 Omentioning

confidence: 99%

Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Kang,

Park

2024

Catalysts

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Methane is an abundant and relatively clean fossil fuel resource; therefore, its utilization as a chemical feedstock has a major impact on the chemical industry. However, its inert nature makes direct conversion into value-added products difficult under mild conditions. Compared to the gas-phase selective oxidation of methane, there have been several recent advances in the liquid-phase conversion of methane. This review categorizes the reports on the liquid-phase selective oxidation of methane according to the solvent and oxidant used. The advantages and disadvantages of each approach are discussed. High yields of methyl bisulfate as a methanol precursor can be achieved using SO3 in sulfuric acid; however, more attention should be paid to the separation process and overall economic analysis. However, the aqueous-phase selective oxidation of methane with in situ generated H2O2 is quite promising from an environmental point of view, provided that an economical reducing agent can be used. Based on the current state-of-the-art on this topic, directions for future research are proposed.

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“…4−6 Various Pd-based catalysts were designed by previous reports to inhibit the dissociation of the O−O bonds at the Pd active site. Priyadarshini et al 7 and Lee et al 8 found that Br can shield the high-energy sites (edges and corners) on the Pd surface, reducing the activation energy for O 2 * dissociation provided by Pd, effectively suppressing the dissociation of the O−O bond. Freakley et al 9 found that SnO 2 can encapsulate a portion of low-coordination small Pd nanoparticles, reducing the number of Pd atoms on the high-energy sites.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Pd Catalytic Activity by Amine Group Modification for Efficient Direct Synthesis of H₂O₂

Ye,

Lin,

et al. 2024

ACS Appl. Mater. Interfaces

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A great deal of research has been carried out on the design of Pd-based catalysts in the direct synthesis of H 2 O 2 , mainly for the purpose of improving the H 2 O 2 selectivity by weakening the activation energy on the Pd active site and thus inhibiting the dissociation of the O−O bonds in O 2 *, OOH*, and HOOH*. However, this often results in insufficient activation energy for the reaction between H 2 and O 2 on Pd, leading to difficulties in improving both the selectivity and productivity of H 2 O 2 simultaneously. Based on this, this study reports an efficient catalyst composed of amine-functionalized SBA-15-supported Pd. The strong metal−support interaction not only makes the PdNPs highly dispersed with more Pd active sites but also improves the stability of the catalyst. The amine group modification increases the proportion of Pd 0 , further enhancing Pd activity and promoting the adsorption and conversion of H 2 and O 2 on Pd, thereby significantly increasing H 2 O 2 productivity. Additionally, the density-functional theory simulation results showed that due to the hydrogen-bonding force between the amine group and H 2 O 2 , this particular anchoring effect would make the hydrogenation and decomposition of H 2 O 2 effectively suppressed. Ultimately, both the selectivity and productivity of H 2 O 2 are improved simultaneously.

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DFT calculations on selectivity enhancement by Br addition on Pd catalysts in the direct synthesis of hydrogen peroxide

Cited by 7 publications

References 48 publications

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Enhancing Pd Catalytic Activity by Amine Group Modification for Efficient Direct Synthesis of H₂O₂

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DFT calculations on selectivity enhancement by Br addition on Pd catalysts in the direct synthesis of hydrogen peroxide

Cited by 7 publications

References 48 publications

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Modeling of Active Sites and Mechanism of Oxidative Coupling of Methane over Alkali Tungstate Catalysts

Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Enhancing Pd Catalytic Activity by Amine Group Modification for Efficient Direct Synthesis of H2O2

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Product

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Enhancing Pd Catalytic Activity by Amine Group Modification for Efficient Direct Synthesis of H₂O₂