Pd or PdO: Catalytic active site of methane oxidation operated close to stoichiometric air-to-fuel for natural gas vehicles

Huang, Fujin; Chen, Jianjun; Hu, Wei; Li, Guangxia; Wu, Yang; Yuan, Shandong; Zhong, Lin; Chen, Yaoqiang

doi:10.1016/j.apcatb.2017.07.037

Cited by 101 publications

(59 citation statements)

References 46 publications

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“…The active phases of catalysts in methane combustion is still under dispute. Several authors had suggested PdO to be the active phase [2,7,12,33,38], while some suggested Pd to be the active phase [26,27,38]. Some researchers [2,4,7,29,39,40] have provided evidences for the existence of PdO x as an active phase during the catalytic combustion of methane.…”

Section: Active Phases and Tentative Mechanismmentioning

confidence: 99%

Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

et al. 2019

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5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD)) under identical conditions. Both catalysts had similar particle sizes and dispersions; the 5-Pd-VM catalyst had 0.5 wt% more Pd loading (4.6 wt%). The surfaces of both catalysts contained PdO and PdOx with about 7% more PdOx in 5-Pd-VM. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscope (SEM) images indicated presence of PdO/PdOx nanocrystals (8–10 nm) on the surface of the support. Size distribution by STEM showed presence of smaller nanoparticles (2–5 nm) in 5-Pd-VM. This catalyst was more active in the lower temperature range of 275–325 °C and converted 90% methane at 325 °C. The 5-Pd-VM catalyst was also very stable after 72-hour stability test at 350 °C showing 100% methane conversion, and was relatively resistant to steam deactivation. Hydrogen TPR of 5-Pd-VM gave a reduction peak at 325 °C indicating weaker interactions of the oxidized Pd species with the support. It is hypothesized that smaller particle sizes, uniform particle distribution, and weaker PdO/PdOx interactions with the support may contribute to the higher activity in 5-Pd-VM.

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Section: Active Phases and Tentative Mechanismmentioning

confidence: 99%

Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

et al. 2019

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“…Some researchers reported PdO as the active Pd species [2,6,7,9,27]. However, others attribute the highest catalytic activity to the Pd metallic state in methane-rich conditions [18,19,27] or to the ratio of Pd to PdO [20,21].…”

Section: Active Phase Of the Catalyst And Proposed Mechanismmentioning

confidence: 99%

“…The BE for Pd 3d5/2 peaks for a 3% PdO/γ-Al 2 O 3 catalyst were in the range 335.2-336.8 ev and assigned to Pd and PdO; a peak with BE of 337.8 ev was due to PdO 2 [3] To the best our knowledge, this is the first research report for the presence of both PdO and Pd native oxide (PdO x ) on the surface of the supported catalyst before reaction. In-situ XPS of a palladium catalyst on La-modified aluminum oxide confirmed PdO as the main surface compound in 'lean (oxygen rich)' conditions [27].…”

Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 99%

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Low-Temperature Activity and PdO-PdOx Transition in Methane Combustion by a PdO-PdOx/γ-Al2O3 Catalyst

et al. 2018

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Abstract:The search to discover a suitable catalyst for complete combustion of methane at low temperature continues to be an active area of research. We prepared a 5 wt % PdO-PdO x /γ-Al 2 O 3 catalyst by a modified Vortex-assisted Incipient Wetness Method. X-ray Photoelectron Spectroscopy showed that the original catalyst contained PdO (38%) and PdO x (62%) on the surface and indicated that PdO x originated from the interaction of PdO with the support. Scanning Transmission Electron Microscopy confirmed the catalyst had an average particle size of 10 nm and was well-dispersed in the support. The catalyst exhibited exceptional low-temperature activities with 90-94% methane conversion at 300-320 • C. The catalyst was active and stable after several catalytic runs with no signs of deactivation by steam in this narrow temperature range. However, the conversion decreased in the temperature range 325-400 • C. The surface composition changed to some extent after the reaction at 325 • C. A tentative mechanism proposes PdO x (Pd native oxide) as the active phase and migration of oxide ions from the support to PdO and then to PdO x during the catalytic oxidation. The high methane conversion at low temperature is attributed to the vortex method providing better dispersion, and to catalyst-support interaction producing the active phase of PdO x .

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“…Palladium and palladium oxide NPs are of very high interest for catalytic combustion [20,21] and more recently for the conversion of biomass molecules into hydrogen and added-value compounds [22][23][24][25]. In this context, the present study examines the MDs of the growth of Pd and PdO NPs in conditions matching those of the Gas Aggregation Source (GAS) setup.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of initial Pd and PdO nanocluster growth in a magnetron gas aggregation source

Brault

Chamorro‐Coral

Chuon

et al. 2019

Front. Chem. Sci. Eng.

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Molecular dynamics simulations are carried out for describing growth of Pd and PdO nanoclusters using the ReaxFF force field. The resulting nanocluster structures are successfully compared to those of nanoclusters experimentally grown in a gas aggregation source. The PdO structure is quasi-crystalline as revealed by HRTEM analysis for experimental PdO nanoclusters. The role of the nanocluster temperature in the MD simulated growth is highlighted.

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Pd or PdO: Catalytic active site of methane oxidation operated close to stoichiometric air-to-fuel for natural gas vehicles

Cited by 101 publications

References 46 publications

Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

Low-Temperature Activity and PdO-PdOx Transition in Methane Combustion by a PdO-PdOx/γ-Al2O3 Catalyst

Molecular dynamics simulations of initial Pd and PdO nanocluster growth in a magnetron gas aggregation source

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