Structure and base properties of calcined hydrotalcites  

作　　者：刘海超 杨锡尧 冉国鹏 闵恩泽 刘建科 应品良 辛勤 李灿 

机构地区：[1]Research Institute of Petroleum Processing, Beijing 100083, China [2]Department of Chemistry, Peking University, Beijing 100871, China [3]State Key Laboratory of Catalysis , Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian, Liaoning 116023, China

出　　处：《Chinese Journal of Chemistry》1999年第4期319-330,1,共12页中国化学（英文版）

摘　　要：Five hydrotalcites with Mg/Al molar ratio range of 3–15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar do and the Calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that A(t) may be mainly from the surface Al. Temperature-programmed desorption (IPD) of CO2 shows that the number of basic sites of Mg(Al)0 samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of basic sites: weak basic OH? sites and strong basic O2 sites on the Mg(Al)0 samples, the base strength depends on the Mg/Al molar do and calcination temperature.Five hydrotalcites with Mg/Al molar ratio range of 3–15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar do and the Calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that A(t) may be mainly from the surface Al. Temperature-programmed desorption (IPD) of CO2 shows that the number of basic sites of Mg(Al)0 samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of basic sites: weak basic OH? sites and strong basic O2 sites on the Mg(Al)0 samples, the base strength depends on the Mg/Al molar do and calcination temperature.

关 键 词：HYDROTALCITES base property CATALYST MAS-NMR 

分 类 号：O611[理学—无机化学]