The Nuclearity of the Active Site for Methane to Methanol Conversion in Cu-Mordenite: A Quantitative Assessment
Dimitrios K. PappasAndrea MartiniMichael DyballaKaroline KvandeShewangizaw TeketelKirill A. LomachenkoRafał BaranPieter GlatzelBjørnar ArstadGloria BerlierCarlo LambertiSilvia BordigaUnni OlsbyeStian SvellePablo BeatoElisa Borfecchia
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Abstract:
The direct conversion of methane to methanol (MTM) is a reaction that has the potential to disrupt a great part of the synthesis gas-derived chemical industry. However, despite many decades of research, active enough catalysts and suitable processes for industrial application are still not available. Recently, several copper-exchanged zeolites have shown considerable activity and selectivity in the direct MTM reaction. Understanding the nature of the active site in these materials is essential for any further development in the field. Herein, we apply multivariate curve resolution analysis of X-ray absorption spectroscopy data to accurately quantify the fraction of active Cu in Cu-MOR (MOR = mordenite), allowing an unambiguous determination of the active site nuclearity as a dicopper site. By rationalizing the compositional parameters and reaction conditions, we achieve the highest methanol yield per Cu yet reported for MTM over Cu-zeolites, of 0.47 mol/mol.Keywords:
Mordenite
Even under normal pressures (1.5–3.0 atm), methanol is formed by the gas phase reaction of methane with oxygen in a flow quartz reactor at 425–490 °C with methanol selectivities exceeding 30% at a methane conversion of 5%.
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Dimethyl ether
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Methane can be converted to methanol over copper-exchanged mordenite at 200 °C. Methanol could be recovered at the end of the reactor. This multi-step reaction opens the possibility for methane to methanol conversion in a closed catalytic cyclic reaction system.
Mordenite
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Methanotrophs in enrichment cultures grew and sustained atmospheric methane oxidation when supplied with methanol. If they were not supplied with methanol or formate, their atmospheric methane oxidation came to a halt, but it was restored within hours in response to methanol or formate. Indigenous forest soil methanotrophs were also dependent on a supply of methanol upon reduced methane access but only when exposed to a methane-free atmosphere. Their immediate response to each methanol addition, however, was to shut down the oxidation of atmospheric methane and to reactivate atmospheric methane oxidation as the methanol was depleted.
Atmospheric methane
Methanotroph
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Mordenite
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X zeolite(X),4A zeolite(A),and natural mordenite(M) were chosen and ion exchanged with Li + and Ca 2+ in aqueous solutions respectively.The selectivity of N 2/O 2 was studied on ion exchanged zeolites using column gas chromatography.The results indicated that the ions contained in zeolites had some pronounced effects on the selectivity of N 2/O 2.CaX and CaA show especially high N 2/O 2 selectivity,and the Li + exchanged natural mordenite also has an obviously improvement on the selectivity of N 2/O 2.TGA and XRD analysis of the materials were carried out and the obtained results combined with structural characters of zeolites were discussed.
Mordenite
Ion chromatography
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Shape-selective synthesis of 2,6-diisopropoylnaphthalene is performed on zeolite mordenite by alkylation of naphthalene with isopropanol. Some modification methods such as ion exchange, de-aluminum, steam disposing, impregnation are used on H-mordenite in order to obtain higher activity and selectivity. The influence of reaction time and temperature along with impregnation on activity and selectivity is also discussed. On the mordenite impregnated with Cesium (Cs) a high conversion of 31.59% and a β-/α- selectivity of 6.8 as well as the selectivity of 2,6-/2,7- of 2.95 are reached.
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