New Evidence for a Dicopper Core within Zeolite Mordenite Side Pockets

• Published in: Journal of physical chemistry. C 2022-03, Vol.126 (12), p.5550-5554
• Main Authors: Crawford, James M, Carreon, Moises A
• Format: Article
• Language: English
• Subjects: C: Chemical and Catalytic Reactivity at Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c10774

Zeolite confinement of metal sites has been widely shown to modify thermocatalytic activity and selectivity. Recently, copper–zeolite combinations have been reported as top performers for the selective catalytic reduction of NO x , direct decomposition of NO to nitrogen, and direct conversion of methane to methanol. The physical and chemical identity of these sites remains disputed, but with the advent of operational analysis, arguments have been made for many active site definitions. Tools including X-ray absorption spectroscopy, DRIFTS, UV–vis–NIR, and resonance Raman have been reported for active site characterization, all providing unique spectroscopic insights. Additionally, chemisorption has been employed to map the acidity of some Cu–zeolites. In this report, we add to the characterization toolkit by proposing a convenient method to evaluate the average nuclearity (copper atoms per occupied framework entity) of activated metal–zeolite combinations, specifically Cu-CHA, Cu-MFI, and Cu-MOR. This was successfully achieved by combining high-resolution microporosity data, zeolite framework arguments, chemisorption analysis, and bulk chemical compositions. In many cases, strong agreement is found between literature-reported copper nuclearity and the proposed physiochemical analysis. The proposed approach could be used in the context of many metal–zeolite combinations as a meaningful characteristic of the active site.