Alkali-activation reactivity of chemosynthetic Al2O3-2SiO2 powders and their 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra

Pure Al2O3-2SiO(2) powders were prepared by sol-gel and coprecipitation methods, and their alkali-activation reactivities were compared. The alkali-activation reactivity of the powder prepared by the sol-gel method was higher than that of the powder prepared by the coprecipitation method. The powders were investigated by Al-27 and Si-29 magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) to understand the relationship between their structure and alkali-activation reactivity. The Al-27 MAS NMR data showed that the five-coordinate Al content of the powder prepared by the sol-gel method was higher than that of the powder prepared by coprecipitation. The higher content of five-coordinate Al corresponded to higher alkali-activation reactivity. The Si-29 MAS NMR data showed that for the powder prepared by the sol-gel method, silicon was replaced by aluminum at secondary coordination sites of the central Si atoms during calcination. However, for the powder prepared by single-batch coprecipitation, the main change was from a low degree of polycondensation to a high degree of polycondensation. (C) 2015 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.