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,