Identifying the location of Cu ions in nanostructured SAPO-5 molecular sieves and its impact on the redox properties

Jörg Radnik, Thi Thuy Hanh Dang, Suresh Gatla, Vikram Singh Raghuwanshi, Dragomir Tatchev, Armin Hoell

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Combining X-ray Absorption Fine Spectroscopy (XAFS) with Anomalous Small-Angle X-ray Scattering (ASAXS) determines the location of Cu2+ ions in silicoaluminophosphate (SAPO-5) frameworks prepared by hydrothermal crystallization or impregnation. As expected, for the hydrothermally prepared sample, incorporation in the SAPO-5 framework was observed. For the first time preferential location of Cu2+ ions at the inner and outer surfaces of the framework is determined. Temperature-Programmed Reduction (TPR) and X-ray Photoelectron Spectroscopy (XPS) investigations demonstrated that such Cu2+ is stable in an argon (Ar) atmosphere up to 550 °C and can only be reduced under a hydrogen atmosphere. In contrast, Cu2+ deposited by impregnation on the pure SAPO-5 framework can be easily reduced to Cu+ in an Ar atmosphere. At lower Cu amounts, mononuclear tetrahedrally coordinated Cu species were formed which are relatively stable in the monovalent form. In contrast, at higher Cu amounts, CuO particles were found which change easily between the mono- and bivalent species.

Original languageEnglish
Pages (from-to)6429-6437
Number of pages9
JournalRSC Advances
Issue number12
Publication statusPublished - 22 Feb 2019
Externally publishedYes

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