Cu-Exchanged Ferrierite Zeolite for the Direct CH4 to CH3OH Conversion: Insights on Cu Speciation from X-Ray Absorption Spectroscopy

• Published in: Topics in catalysis 2019-08, Vol.62 (7-11), p.712-723
• Main Authors: Pappas, Dimitrios K., Borfecchia, Elisa, Lomachenko, Kirill A., Lazzarini, Andrea, Gutterød, Emil S., Dyballa, Michael, Martini, Andrea, Berlier, Gloria, Bordiga, Silvia, Lamberti, Carlo, Arstad, Bjørnar, Olsbye, Unni, Beato, Pablo, Svelle, Stian
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Activation; Aluminum; Catalysis; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Conversion; Copper; Industrial Chemistry/Chemical Engineering; Methane; Original Paper; Pharmacy; Physical Chemistry; Reduction; Silicon; Speciation; Spectrum analysis; X ray absorption; X-ray spectroscopy; Zeolites
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-019-01160-7

The direct stepwise transformation of CH 4 to CH 3 OH over Cu-exchanged zeolites has been an intensively researched reaction as it can provide a solution for the utilization of this abundant feedstock. Up to date a commercial process is far from realization, which is why an understanding of the Cu speciation in zeolites as a function of reaction conditions as well as the development of a mechanistic view of the reaction are necessary to further advance the field. Herein we study Cu-exchanged ferrierite zeolite for the direct CH 4 to CH 3 OH conversion by utilizing X-ray absorption spectroscopy (XAS), in order to assess the local structure and electronic properties of Cu through the reaction. A Cu-FER sample with a Cu/Al = 0.20 and Si/Al = 11 was subjected to three reaction cycles yielding ultimately 96 µmol C H 3 OH / g zeolite . Normalized to the Cu loading, this accounts for 0.33 mol C H 3 OH /mol Cu , making the sample comparable to very active Cu-MOR materials reported in the literature. During O 2 activation, a transient self-reduction regime of Cu II to Cu I ions was identified; eventually leading to mostly framework interacting Cu II species. CH 4 loading leads to a reduction of these Cu II containing species; which are finally partially reoxidized during H 2 O-assisted CH 3 OH extraction. The speciation after CH 4 activation as well as H 2 O-assisted CH 3 OH extraction was assessed via linear combination fitting analysis of the XAS data.