Mechanistic study on the methane activation over various supported molybdenum carbide catalysts with isotopic tracer methods

Naito, Shuichi; Takada, Akiko; Tokizawa, Satoshi; Miyao, Toshihiro

doi:10.1016/j.apcata.2005.04.011

Cited by 21 publications

(10 citation statements)

References 16 publications

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“…280−320 ppm can probably be attributed to the initial β-Mo 2 C impurity phase and/or partial sintering of the catalyst to bulk β-Mo 2 C. Interestingly, a dramatic decrease in the signal-tonoise ratio is likely due to an exchange of the carbide carbon during the WGS reaction, yielding a substitution of 13 C by 12 C form the feed. A similar participation of the carbide carbon was previously observed in CO hydrogenation, 58 methane partial oxidation, 59 and methane dry reforming 60…”

Section: ■ Results and Discussionsupporting

confidence: 82%

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

et al. 2019

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MXenes, a recently discovered family of two-dimensional (2D) materials, are promising catalysts and supports for applications in heterogeneous catalysis; however, the thermal stability of MXenes and their surface chemistry are not fully explored. Here, we report that 2D molybdenum carbide Mo2CT x remains stable and shows no appreciable sintering up to ca. 550–600 °C in a reducing environment, as assessed by a combined in situ X-ray absorption near-edge spectroscopy (XANES) and powder X-ray diffraction (XRD) study during a temperature-programmed reduction (TPR) experiment. At higher temperatures, the passivating oxo, hydroxy, and fluoro groups defunctionalize the molybdenum-terminated surface, inducing a transformation to bulk β-Mo2C that is complete at ca. 730 °C. We demonstrate that Mo2CT x is a highly stable and active catalyst for the water–gas shift reaction with a selectivity >99% toward CO2 and H2 at 500 °C. The conversion of carbon monoxide on Mo2CT x starts to decline at temperatures that are associated with the decrease of the interlayer distance between the carbide sheets, as determined by the XRD-probed TPR, indicative of increasing mass transfer limitations at these conditions. Our results provide an insight into the thermal stability and reducibility of Mo2CT x and serve as a guideline for its future catalytic applications.

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Section: ■ Results and Discussionsupporting

confidence: 82%

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

et al. 2019

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“…However, the formation mechanism of coal tar in the CRMP process is not yet clear. Catalytic conversion of methane, especially CO 2 reforming of methane to produce H 2 and CO for Fischer−Tropsch synthesis, has been studied in the field of heterogeneous catalysis. − The stable isotope analysis was also reported to explain the mechanism of the CO 2 reforming of methane (CRM) process. − In their studies, with deuterated methane (CD 4 ) and CH 4 used in the CRM process, CH 3 D, CH 2 D 2 , and CHD 3 can be detected.…”

Section: Introductionmentioning

confidence: 99%

Isotope Analysis for Understanding the Tar Formation in the Integrated Process of Coal Pyrolysis with CO₂ Reforming of Methane

et al. 2010

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In our previous studies, a higher tar yield can be obtained from a novel integrated process of coal pyrolysis with CO2 reforming of methane (CRMP) than the traditional coal pyrolysis process. However, the tar formation mechanism in the CRMP process was not yet clear. In this work, deuterated methane (CD4) was used to investigate the formation mechanism of coal tar in the integrated process through analyzing the chemical compounds of coal tar with gas chromatography and mass spectrometry (GC/MS) analysis. The results showed that deuterium was detected in the main compounds of tar with the existing form of [•D] and [•CD3]. Deuterium in CD4 took part in the formation of coal tar compounds, indicating that the atmosphere took an important role in the formation of coal tar. When the formation process of certain compounds was analyzed, it can be deduced that the higher coal tar yield in the CRMP process can be attributed to the interaction of free radicals formed from the CO2 reforming of methane and from the cracking of the coal chemical structure in pyrolysis.

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“…• refining the calibration at low temperatures (Larson and Hall, 1965;Robertson et al, 1975;Golden et al, 2001;Naito et al, 2005); • experiments to retrieve kinetics associated with the breaking and reforming of C-H bonds (Koepp, 1978;Lyon and Hulston, 1984;Reeves et al, 2012); • construction of numerical models to test hypotheses regarding biophysical controls on isotopologue abundances. Through this work, we have also realized that there is much more information to be extracted from simple gas chemistry and conventional stable isotope data than has perhaps been widely appreciated; or that has been somewhat overlooked in the rush to develop and deploy new technologies.…”

Section: Discussionmentioning

confidence: 99%

The geochemistry of methane isotopologues

Wang¹

2017

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This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12 CH 4 , 13 CH 4 , 12 CH 3 D, and 13 CH 3 D record the formation, transport, and breakdown of methane in selected settings.Chapter 2 reports precise determinations of 13 CH 3 D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13 CH 3 D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped-and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H 2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13 CH 3 D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow-and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300• C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O 2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13 C/ 12 C and D/H isotope fractionation factors alone.: Shuhei Ono, Ph.D. Acknowledgments I fear that this section will not do justice to the people I have not the space to thank individually. Alas, here goes. To those whose names are not specifically listed here, thank you too. I wish first to thank Shuhei Ono. The work this thesis represents could not have happened without his bold vision and the license to explore and question that working in his lab afforded. His unbridled optimism, breadth of scientific curiosity, personal integrity, and accessibility to his personnel are traits I one day hope to emulate. I thank him for his nonjudgmental yet appropriately measured support of many of my ideas-even those that led nowhere-, for believing in me even when I found it difficult to do so myself, and for teaching me to change pump oil, build vacuum lines, and drink Icelandic vodka.I also wish to thank my thesis committee members Jeff Seewald, Roger Summons, and John Pohlman, for their in...

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Mechanistic study on the methane activation over various supported molybdenum carbide catalysts with isotopic tracer methods

Cited by 21 publications

References 16 publications

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

Isotope Analysis for Understanding the Tar Formation in the Integrated Process of Coal Pyrolysis with CO₂ Reforming of Methane

The geochemistry of methane isotopologues

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Mechanistic study on the methane activation over various supported molybdenum carbide catalysts with isotopic tracer methods

Cited by 21 publications

References 16 publications

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo2CTx: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo2CTx: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

Isotope Analysis for Understanding the Tar Formation in the Integrated Process of Coal Pyrolysis with CO2 Reforming of Methane

The geochemistry of methane isotopologues

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Product

Resources

About

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

In Situ XANES/XRD Study of the Structural Stability of Two-Dimensional Molybdenum Carbide Mo₂CT_x: Implications for the Catalytic Activity in the Water–Gas Shift Reaction

Isotope Analysis for Understanding the Tar Formation in the Integrated Process of Coal Pyrolysis with CO₂ Reforming of Methane