Methane oxidation on Pd–Ceria: A DFT study of the mechanism over PdxCe1−xO2, Pd, and PdO

Mayernick, Adam D.; Janik, Michael J.

doi:10.1016/j.jcat.2010.11.006

Cited by 151 publications

(125 citation statements)

References 45 publications

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“…[16][17][18][19] The active phase of Pd for CH 4 combustion has been investigated by DFT calculations and in situ SXRD experiments. It was found that the PdO(101) facet develops preferentially during the oxidation of Pd(100) 17,18 and that the formation of PdO(101) coincides with increased rates of methane oxidation during reaction at millibar pressures. 19 In addition to these studies of PdO nanoparticles or surfaces, the gas-phase C-H bond activation of CH 4 by various single transition-metal-oxide ions and bare metal cations has been experimentally and theoretically investigated by a large number of groups.…”

Section: Introductionmentioning

confidence: 99%

“…19 In addition to these studies of PdO nanoparticles or surfaces, the gas-phase C-H bond activation of CH 4 by various single transition-metal-oxide ions and bare metal cations has been experimentally and theoretically investigated by a large number of groups. [16][17][18][19][20][21][22][23] Schwarz's group has systematically examined the efficiency and product branching ratio of the gas phase reactions of various transition metal oxide ions with methane. It was found that transition metal oxide ions ScO + , TiO + , VO + and CoO + do not react, while other transition metal oxide ions, MnO + , FeO + , NiO + , PtO + and OsO + , react with methane to give methanol.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

et al. 2017

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Abstract:A theoretical analysis was carried out on the mechanism of methane oxidation to methanol occurring on single site palladium oxide species [PdO] 2+ supported on a model of Al-MCM-41 silica. Both 6 and 8-membered ring structures were considered to represent the support.The energy profile for each elementary reaction was determined from density functional theory calculations with the OPBE functional. The calculated overall activation energies are close to the experimental values. Our calculations confirm that spin inversion can play a significant role in decreasing the barrier heights for the pathways. Indeed, in this type of reactions we could show a crossing between singlet and triplet reaction paths. We showed that the mechanism for the C-H bond cleavage and for the formation of methanol has a radical nature. According to our results, the [PdO] 2+ species located on a 8-membered ring of silica is more active than that deposited on a 6-membered ring. The calculated activation energies to cleave the methane C-H bond are 35 and 84 kJ/mol for the radical and ionic pathways, respectively. The activation barrier and the transition state geometry of this H-abstraction step are directly correlated with the optimal angle at which the substrate should approach the [Pd=O] 2+ moiety, with the elongation of the Pd-O oxo bond and finally with the energy of the π* acceptor orbital.2

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

et al. 2017

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“…In case of palladium, a Mars-vanKrevelen mechanism is proposed, where palladiums´ bulk oxygen is involved [23]. The formation of methyl species is commonly assumed as the overall rate determining reaction step [24].…”

Section: Introductionmentioning

confidence: 99%

Removal of oxygen from (bio-)methane via catalytic oxidation of CH 4 —Reaction kinetics for very low O 2 :CH 4 ratios

Ortloff

Bohnau

Graf

et al. 2016

Applied Catalysis B: Environmental

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“…[8,10] Ceria (CeO 2 ) is one of the most effective promoters for Pd oxidation among oxides used as a support and it can, therefore, play a pivotal role in enhancing catalytic stability and activity for methane combustion. [11,12] CeO 2 is known to have two beneficial functions: it provides oxygen for the catalytic combustion at low temperature by transferring oxygen to Pd [9,13,14] and it can improve the stability of the active PdO phase at high temperatures. [15][16][17] However, pure ceria has limited thermal stability, [18] and direct contact between the ceria and Pd is required for oxygen transfer.…”

Section: Introductionmentioning

confidence: 99%

Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water

et al. 2014

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The influence of water vapor on methane catalytic combustion was studied over a Pd@CeO2/Si‐Al2O3 catalyst, carefully designed to maximize Pd‐CeO2 interaction and prevent metal sintering and compared to a conventional impregnated catalyst with identical chemical composition. Although the nanostructured Pd@CeO2/Si‐Al2O3 catalyst is thermally stable, the addition of water to the reaction feed leads to a transient deactivation at low temperatures, consistent with the well documented competitive adsorption. In addition to this, the hierarchically structured catalyst exhibits an additional severe deactivation after methane oxidation in the presence of water vapor at 600 °C that can be reversed only by heating the catalyst above 700 °C. The presence of water in the reaction feed deactivates the conventional impregnated catalyst less severely and the activity largely returns upon water removal. Catalytic FTIR and CO‐chemisorption data indicate that this severe deactivation process in the hierarchical catalyst is due to the formation of stable OH groups on the surface of the ceria nanoparticles. These hydroxyl groups are suggested to significantly inhibit the oxygen spillover from the CeO2 nanoparticles to Pd, preventing its efficient re‐oxidation, as observed by operando X‐ray absorption near edge spectroscopy (XANES) experiments. At the same time, their presence can contribute to limit the gas phase accessibility of Pd, as indicated by the decrease of CO chemisorption capability. The presence of hydroxyls plays a minor role on the deactivation of the conventional catalyst at 600 °C.

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Methane oxidation on Pd–Ceria: A DFT study of the mechanism over PdxCe1−xO2, Pd, and PdO

Cited by 151 publications

References 45 publications

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

Removal of oxygen from (bio-)methane via catalytic oxidation of CH 4 —Reaction kinetics for very low O 2 :CH 4 ratios

Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water

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Methane oxidation on Pd–Ceria: A DFT study of the mechanism over PdxCe1−xO2, Pd, and PdO

Cited by 151 publications

References 45 publications

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

Oxidation of Methane to Methanol over Single Site Palladium Oxide Species on Silica: A Mechanistic view from DFT

Removal of oxygen from (bio-)methane via catalytic oxidation of CH 4 —Reaction kinetics for very low O 2 :CH 4 ratios

Methane Catalytic Combustion over Hierarchical Pd@CeO2/Si‐Al2O3: Effect of the Presence of Water

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Methane Catalytic Combustion over Hierarchical Pd@CeO₂/Si‐Al₂O₃: Effect of the Presence of Water