Structure and base properties of calcined hydrotalcites |
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| Authors: | LIU Hai-Chao YANG Xi-Yao RAN Guo-Peng MIN En-ZeResearch Institute of Petroleum Processing Beijing China |
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| Affiliation: | LIU,Hai-Chao YANG,Xi-Yao RAN,Guo-Peng MIN,En-ZeResearch Institute of Petroleum Processing,Beijing 100083,China Department of Chemistry,Peking University,Beijing 100871,China LIU,Jian-Ke YING,Pin-Liang XIN,Qin LI,CanState Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian,Liaoning 116023,China |
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| Abstract: | 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)0, and its amount increases with the Mg/Al molar ratio 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 Al(t) may be mainly from the surface Al. Temperature-programmed desorption (TPD) of CO2 shows that the number of basic sites of Mg(Al)O 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)O samples, the base strength depends on the Mg/Al molar ratio and calcination temperature. |
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| Keywords: | Hydrotalcites base property catalyst MAS-NMR FT-IR. |
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