(298a) Copper Speciation in Cu-Mordenite Catalysts for the Oxidation of Methane to Methanol

Authors: 
Brezicki, G., University of Virginia
Davis, R. J., University of Virginia
Kammert, J. D., University of Virginia
Paolucci, C., University of Virginia
Gunnoe, T. B., University of Virginia
Wang, Y., Fritz Haber Institute
Kröhnert, J., Fritz Haber Institute
Trunschke, A., Fritz-Haber-Institute of the Max-Planck-Society
Schlögl, R., Fritz Haber Insitute of the Max Planck Society
Methane from abundant natural gas reserves represents a valuable potential feedstock for the chemical industry, but the requirement of liquefying natural gas for storage and transport renders much of the gas present in remote deposits economically inaccessible. Copper-exchanged zeolite catalysts are capable of chemically converting CH4 to higher-value liquid CH3OH with high selectivity, but low yields have prevented industrial application and hampered active site characterization. Utilizing the H+ form of the zeolite instead of the Na+ form has been shown to increase CH3OH productivity, which should facilitate identification of the Cu active site, but the active site structure in Cu-H-MOR has not yet been unambiguously defined. Under conditions of high CH4 pressure, the C1 product yield during cyclic operation of the Cu-H-MOR catalyst was 0.42 mol (mol Cu)-1. Linear combination fitting of the Cu K-edge X-ray absorption spectrum of the Cu-H-MOR catalyst showed that 83% of the Cu was auto-reduced in He, which is assumed to be the redox-active fraction of Cu for CH3OH formation. Normalizing the product yield to the redox-active fraction of Cu gave a reaction stoichiometry of 0.50 mol (mol Cu)-1, consistent with the presence of dicopper active sites. The O2-activated dicopper sites were further characterized by EXAFS, UV-vis and resonance-Raman spectroscopy.
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