Exchanged oxo-Cu2+cations in mordenite zeolites: Evidencing the truly active in the stepwise conversion of methane to methanol from in situ DRS-UV-vis analyses performed during activation and reaction

Author(s)

Picinini, Monize ; dos Santos, Mateus Gonsalves ; Bueno, Jose Maria C. ; Urquieta-Gonzalez, Ernesto A.

• Document type: Journal article
• Source: MOLECULAR CATALYSIS; v. 579, p. 14-pg., 2025-05-15.

Abstract

After activation, Cu2+-exchanged zeolites generate exchanged oxo-Cu2+ cations that absorb UV-vis radiation in all of the d-d and LMCT transitions range. On the other hand, based on great experimental and/or theoretical data, bi- or trinuclear exchanged oxo-Cu2+-zeolites with attributed absorption UV-vis bands centered between 20,000 and 35,000 cm-1, are the mainly considered as the potential active species to directly convert methane to methanol (MTM) in a stepwise process, which obviously leads to low copper specific activities (TON). What about the others generated oxo-Cu2+ cations? To elucidate this question, we developed a systematic study using catalytic evaluation data of oxo-Cu2+ mordenites and in situ DRS-UV-vis analyses performed during air activation at 550 degrees C and MTM conversion at 200 degrees C. The obtained data allowed to confirm that the less-generated oxo-Cu2+ cations related to absorption DRS-UV-vis bands centered at wavenumbers lower than 33,000 cm-1, are the effectively active species to directly oxidize the methane molecule to methanol, but also evidencing that the most generated oxo-Cu2+ cations are poorly active, thus explaining the reported low copper TON values of activated Cu2+-exchanged zeolites. This finding must stimulate the involved scientific community to find more effective activation procedures that can promote the formation of such more active oxo-Cu2+ cations. (AU)

• FAPESP's process: 21/12394-0 - Sustainable synthetic methods employing catalysis, benign solvents, safer reagents, and bio-renewable feedstock
• Grantee: Arlene Gonçalves Corrêa
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 18/01258-5 - Novel chemical catalytic and photocatalytic processes for the direct conversion of methane and CO2 to products
• Grantee: José Maria Correa Bueno
• Support Opportunities: Research Projects - Thematic Grants