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NMR and acidity studies of dealuminated metakaolin and their correlation with cumene cracking

1994; Elsevier BV; Volume: 8; Issue: 5 Linguagem: Inglês

10.1016/0169-1317(94)90022-1

1872-9053

JoséCarlos D. Macedo, Cláudio J. A. Mota, S DEMENEZES, V CAMORIM,

CO2 Sequestration and Geologic Interactions

Metakaolin is obtained by dehydroxylation of kaolin; its dealumination is carried out with sulfuric acid. 29Si MAS NMR studies show that a three-dimensional framework of SiO4 is formed with an increase in kaolin calcination temperature. On the other hand, 27Al MAS NMR shows that calcination temperatures up to 850°C bring on a decrease of the hexa-coordinated aluminum nuclei, while tetra- and penta-coordinated aluminum nuclei are being formed. In the range of temperatures studied, the amount of Brönsted sites are not constant and decrease up to 850°C, probably because the metakaolin structure undergoes less collapse during acid attack. A synergism between Lewis and Brönsted sites is suspected. Thus, it is suggested that penta-coordinated aluminum nuclei, which are strong Lewis sites, increase the strength of Brönsted sites. Consequently, cumene cracking activity increases.