Meeting Program — February 2015
Department of Chemical and Biomolecular Engineering
University of Delaware
Methanotrophic bacteria containing particular methane monooxygenase (pMMO), a Cu-containing enzyme, or soluble methane monooxygenase (sMMO), an iron-metalloenzyme can oxidize methane to methanol selectively at ambient conditions 1. The zeolite Cu-ZSM-5 was reported to activate the methane C-H bond—with a homolytic bond dissociation energy of 104 kcal/mol— at temperatures as low as 120 °C 2 after pretreatment in O2 3. The reactive copper species are believed to contain extra-lattice oxygen, and in the case of Cu-ZSM-5, to be a mono-μ-oxo-dicopper complex ([Cu—O—Cu]2+) 4. Although a correlation was found between the concentration of mono-μ-oxo-dicopper species and the amount of methanol produced by Cu-ZSM-5 5, no such correlation was found for other zeolites that produce methanol such as Cu-mordenite and Cu-ferrierite 2. We have recently showed methanol production on copper (II) exchanged small pore zeolites including SSZ-13 (CHA), SSZ-16 (AFX) and SSZ-39 (AEI) with yields as high as 39 μmol CH3OH/g and CH3OH/Cu ratios up to 0.09 (the largest reported to date).6 Here, copper species in these small pore zeolites were investigated with UV–vis and Raman spectroscopy after O2-treatment at a temperature of 450 °C. No evidence of mono-μ-oxo-dicopper species was found in the spectra of Cu-SSZ-13,Cu-SSZ-16 and Cu-SSZ-39 6, however Cu—Oextralattice vibrations at 574 cm-1 were detected in Raman spectra of Cu-SSZ-13 and Cu-SSZ-39 zeolites which is indicative of a different CuxOy active species responsible for methanol production in small pore zeolites.
1. Hanson, R. S.; Hanson, T. E., Methanotrophic Bacteria. Microbiological Reviews
1996, 60, 439–471.
2. Smeets, P. J.; Groothaert, M. H.; Schoonheydt, R. A., Cu based zeolites: A UV–vis
study of the active site in the selective methane oxidation at low temperatures.
Catal. Today 2005, 110 (3–4), 303–309.
3. Groothaert, M. H.; Smeets, P. J.; Sels, B. F.; Jacobs, P. A.; Schoonheydt, R. A.,
Selective Oxidation of Methane by the Bis(mu-oxo)dicopper Core Stabilized on
ZSM-5 and Mordenite Zeolites. Journal of American Chemical Society 2005, 127,
4. Woertink, J. S.; Smeets, P. J.; Groothaert, M. H.; Vance, M. A.; Sels, B. F.;
Schoonheydt, R. A.; Solomon, E. I., A [Cu2O]2+ core in Cu-ZSM-5, the active site in
the oxidation of methane to methanol. Proceedings of the National Academy of
Sciences of the United States of America 2009, 106 (45), 18908–13.
5. Beznis, N. V.; Weckhuysen, B. M.; Bitter, J. H., Cu-ZSM-5 Zeolites for the Formation
of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator
Species. Catal. Lett. 2010, 138 (1–2), 14–22.
6. Wulfers, M. J.; Teketel, S.; Ipek, B.; Lobo, R. F., Conversion of Methane to Methanol
on Copper Containing Small Pore Zeolites and Zeotypes. Chem Commun 2015, xx,