The 27 Al State in CeO2-γ-A12O3 Mixed Oxides Determined by Solid-State NMR Spectroscopy
用固体核磁共振方法研究CeO2-γ-Al2O3混合氧化物中的Al状态

In this work, CeO2-γ-Al2O3 mixed oxides were studied by solied 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 tera- and hexa-coordinated 27Al sites. It was demon-strated that the sharp peak at ca.37 ppm originates from the 27Al atomes residing in the lattice of CeO2 with an eigh-fold coordinatio, 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 cell so that the overall charge balance of the systerm is maintained. Further-more,it was shown that the concentration of Al substitution is limited, and only about 1% of the total CeO2 can be replaced by Al3+.