用固体核磁共振方法研究CeO2-γ-Al2O3混合氧化物中的Al状态

摘要

用固体核磁共振技术研究了CeO2-γ-Al2O3混合体系中CeO2和γ-Al2O3两相间的相互作用.在混合物的27 Al MAS NMR中,除了四配位和六配位的Al位外,有一个尖锐的位于37处的峰,这个峰在高场处有一宽的肩峰.实验证实:位于高场的宽峰来自于γ-Al2O3中的五配位Al,而位于37处的尖峰则是由CeO2和γ-Al2O3 两相问的相互作用产生的,即Al取代了CeO2晶格中八配位的Ce.定量研究表明,这种Al取代的量是极其有限的,整个CeO2晶格只有1%的Ce能被Al取代.%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+.