Abstract: In this work, CeO₂-γ-Al₂O₃ mixed oxides were studied by solid-state NMR techniques to understand the interaction between CeO₂ and γ-Al₂O₃. The ²⁷Al magic angle spinning (MAS) NMR spectra of the mixed oxides showed a sharp peak at ca. 37 ppm and a highfield shoulder, in addition to the signals from tetra- and hexa-coordinated ²⁷Al sites. It was demonstrated that the sharp peak at ca. 37 ppm originates from the ²⁷Al atoms residing in the lattice of CeO₂ with an eightfold coordination, representing the interaction between CeO₂ and γ-Al₂O₃; the highfield broad shoulder peak arises from penta-coordinated Al sites originally present in γ-Al₂O₃. It was postulated that four ^_Al3+ ions have replaced the three Ce⁴⁺ ions in three CeO₂ crystal cells so that the overall charge balance of the system is maintained. Furthermore, it was shown that the concentration of Al substitution is limited, and only about 1% of the total CeO₂ can be replaced by Al³⁺.

Key words: ²⁷Al MAS NMR, CeO₂, γ-Al₂O₃, substitution, MQMAS NMR