Selective Oxidation of Methane by the Bis(μ-oxo)dicopper Core Stabilized on ZSM-5 and Mordenite Zeolites

Abstract

This work reports on the capability of the O2-activated Cu-ZSM-5 and Cu-MOR zeolites to selectively convert methane into methanol at a temperature of 398 K. A strong correlation between (i) the activity and (ii) the intensity of the 22 700 cm-1 UV-vis band, assigned to the bis(mu-oxo)dicopper core, is found (i) as a function of the reaction temperature, (ii) as a function of the Cu loading of the zeolite, and (iii) in comparison to other Cu materials. These three lines of evidence firmly support the key role of the bis(mu-oxo)dicopper core in this selective, low-temperature hydroxylation of methane.

A [Cu 2 O] 2+ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol

“…1 blue). These isotope-sensitive vibrations involve the active oxygen species, as the reaction of the 18 O 2 -generated active site with CH 4 results in CH 3 18 OH formation (5 ). An intense isotope-insensitive feature is also observed at 514 cm Ϫ1 with a shoulder near 540 cm Ϫ1 .…”

“…O 2 and He treatments at 450°C were done following procedures reported in ref. 5. The UV-vis spectra after interaction of a dehydrated Cu-ZSM-5 (Cu/Al ϭ 0.54, dehydrated at 450°C in He) with N 2O and O2 at temperatures Ͻ250°C were recorded after the sample was flushed at room temperature with O 2 or N2O (5 min, 100vol.% O2 or N2O flow of 50 mL⅐min Ϫ1 ) and heated under this closed atmosphere (5°C min Ϫ1 to the indicated temperature).…”

“…Recently, an O 2 -activated zeolite Cu-ZSM-5 has been shown to convert methane to methanol at low temperatures (100°C) with selectivity Ͼ98% (5). Reactivity only occurs at a small fraction of the total copper sites in the zeolite (5). Researchers have attempted to determine the identity of the active copper-oxygen core, although the challenge of distinguishing it from spectator sites has not been overcome and no consensus has been reached as to its structure (6 -8).…”

Direct Methylation of Benzene with Methane Catalyzed by Co/MFI Zeolite

“…(2)), was found to proceed on H‐ and Na‐MFI and its ion exchanged formed with Co, Mn and Cu salts;32,33 the valence of transition elements has not been mentioned in the papers. Also for the partial oxidation of methane into methanol, zeolite‐supported transition metal species were reported to show the catalytic activity 34, 35, 36, 37, 38. It has been known that zeolite (mainly MFI)‐supported metal species are active also for combustion of methane,39 reduction of NO x with methane,40 aromatization of methane14 and the activation of methane at low temperature 41.…”

How fracking is upending the chemical industry

“…In 2005, however, a team led by Robert Schoonheydt at the University of Leuven in Belgium, found 4 that copper seeded onto a porous material called a zeolite could unite oxygen and methane to make methanol at less than 200 °C. Crucially, the methanol became trapped in the zeolite's pores, preventing further reactions.…”