Evolution of active sites during selective oxidation of methane to methanol over Cu-CHA and Cu-MOR zeolites as monitored by operando XAS

Borfecchia, Elisa; Pappas, Dimitrios; Dyballa, Michael; Lomachenko, Kirill A.; Negri, Chiara; Signorile, Matteo; Berlier, Gloria

doi:10.1016/j.cattod.2018.07.028

Cited by 70 publications

(124 citation statements)

References 54 publications

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“…In contrast, the methoxy species and molecularly adsorbed methanol demonstrate high stability to over‐oxidation at high temperature, probably due to the low mobility of these species and hence disabling their diffusion and reaction over the Cu II ‐oxo active sites. Other products, such as aromatic or aliphatic compounds, were not observed at high temperature, which is consistent with previous studies reporting the exclusive formation of methanol and carbon oxides during methane oxidation over copper‐exchanged mordenite …”

Section: Resultssupporting

confidence: 92%

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Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

2019

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The reaction of methane with copper‐exchanged mordenite with two different Si/Al ratios was studied by means of in situ NMR and infrared spectroscopies. The detection of NMR signals was shown to be possible with high sensitivity and resolution, despite the presence of a considerable number of paramagnetic CuII species. Several types of surface‐bonded compounds were found after reaction, namely molecular methanol, methoxy species, dimethyl ether, mono‐ and bidentate formates, CuI monocarbonyl as well as carbon monoxide and dioxide, which were present in the gas phase. The relative fractions of these species are strongly influenced by the reaction temperature and the structure of the copper sites and is governed by the Si/Al ratio. While methoxy species bonded to Brønsted acid sites, dimethyl ether and bidentate formate species are the main products over copper‐exchange mordenite with a Si/Al ratio of 6; molecular methanol and monodentate formate species were observed mainly over the material with a Si/Al ratio of 46. These observations are important for understanding the methane partial oxidation mechanism and for the rational design of the active materials for this reaction.

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Section: Resultssupporting

confidence: 92%

“…Numerous copper‐exchanged zeolites, including CuMFI, CuMOR, CuFAU, CuMAZ, and CuCHA, were tested and revealed different methanol yields and selectivity per cycle. The research targeting the achievement of the highest methanol productivity allowed to obtain the methanol productivity close to the theoretical limit .…”

Section: Introductionmentioning

confidence: 99%

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

2019

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“…Different zeolites are known to possess the active Cu site motifs capable of the conversion. Cu–MOR,–,, Cu‐ZSM‐5,, and Cu‐SSZ‐13,,, exhibit high yields with the maximum being 0.47, 0.21 and 0.172 (molCH 3 OH/molCu) for each topology respectively. Due to the stoichiometric nature of the process, the CH 3 OH output is inevitably dictated by the density and nuclearity of the active sites.…”

Section: Introductionmentioning

confidence: 98%

“…Initially the materials are activated at high temperature, typically above 400 °C, in the presence of O 2 leading to the formation of Cu‐oxo species . Then CH 4 is loaded at lower temperature (200 °C) and finally CH 3 OH is extracted online by introducing steam to the reactor ,,,…”

Section: Introductionmentioning

confidence: 99%

Understanding and Optimizing the Performance of Cu‐FER for The Direct CH₄ to CH₃OH Conversion

et al. 2018

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Cu‐exchanged zeolites with the Ferrierite topology were investigated in the direct CH4 to CH3OH conversion. Samples with a systematic compositional variation in terms of Na/Al and Cu/Al ratios where synthesized by liquid ion exchange. The presence of Na is observed to be beneficial for the Cu exchange and thereby higher Cu loadings were achieved. The overall performance of Cu‐FER samples depends on Cu loading as well as the conditions of the reaction. Elevated O2 activation temperature as well as long CH4 loading times are proven to enhance the CH3OH yield of the Cu‐FER sample with Cu/Al=0.2. In addition, the productivity depends on the Cu/Al ratio, at low values the sample is almost inactive indicating a Cu threshold that needs to be surpassed. We employed X‐ray absorption and IR of adsorbed CO spectroscopies in order to rationalize the performance as well as the effect of Cu/Al ratio. From the in situ spectroscopies we ultimately establish structure‐activity relationships between the reducibility of Cu species and the CH3OH yield.

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“…10,11 The field advanced greatly over the years, and promising results were obtained mainly with copper based catalysts, either on zeolites 12,13 or metal-organicframework 14 supports. Generally, this process requires high temperatures and operating pressures.…”

Section: Introductionmentioning

confidence: 99%

Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

et al. 2019

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Summary Natural gas from stranded sources is being predominantly flared, and there is a growing demand for new technologies for its utilisation, where electrification, flexibility, and modularity play an important role. Plasma‐activated methane partial oxidation reaction was studied in a designed dielectric barrier discharge ionisation reactor unit, producing value‐added platform chemicals, namely, methanol, formaldehyde, intermediate formic acid, acetic acid, and paraformaldehyde at ambient temperature and atmospheric pressure. The effects of various process parameters, such as voltage, total convertible gas flow rate, and reagent ratio relationship, were considered. In addition, coupling of the following catalytic materials with plasma was examined: alumina (Al2O3), chabazite, ferrierite, microporous beta zeolite, silica (SiO2) glass beads, ZSM‐5 (MFI), Fe on H‐ZSM‐5 and Al2O3, Mo on H‐ZSM‐5, TiO2 and SiO2, and Pd on Al2O3. In the liquid product, 21.5% CH3OH, 20.4% CH2O, 0.3% HCOOH, and 2.4% CH3COOH were measured when using pure plasma, and a maximum aggregate yield of the organic oxygenate compounds of 5.21 mol.% was achieved. The usage of shaped silicate surface increased the selectivity towards synthesised oxygen‐containing structures, while the application of alumino‐silicate mixture constituents reduced it. It was determined that elementary covalently bonded carbon was formed inside pores when pure zeolites were used. Fe‐ and Pd‐based heterogeneous catalysts favoured the complete exothermic combustion of CH4 feedstock reactant species, and the liquid product consisted only of water in the Pd‐ case. The utilisation of Mo/H‐ZSM‐5 resulted in a 46% increased yield of formalin. A mechanism for the role of Mo was proposed, where Mo oxidises methanol to formaldehyde and the metal is reoxidised in plasma.

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Evolution of active sites during selective oxidation of methane to methanol over Cu-CHA and Cu-MOR zeolites as monitored by operando XAS

Cited by 70 publications

References 54 publications

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

Understanding and Optimizing the Performance of Cu‐FER for The Direct CH₄ to CH₃OH Conversion

Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

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Evolution of active sites during selective oxidation of methane to methanol over Cu-CHA and Cu-MOR zeolites as monitored by operando XAS

Cited by 70 publications

References 54 publications

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

Understanding and Optimizing the Performance of Cu‐FER for The Direct CH4 to CH3OH Conversion

Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

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Product

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Understanding and Optimizing the Performance of Cu‐FER for The Direct CH₄ to CH₃OH Conversion