Investigation of coke deposits on Al-MCM-41

Carbonaceous compounds deposited on aluminosilicate mesoporous molecular si eves of the MCM-41 type during conversion of cyclohexene at various tempera tures were investigated using TGA; DRIFT, UV-vis, and C-13 Solid State NMR spectroscopies; and a sorption technique. The chemical composition of the d eposits is not significantly affected by the Al content of Al-MCM-41 and de pends mainly on the temperature and the duration of the reaction. At lower applied temperatures, both aliphatic and aromatic compounds are formed; the y are relatively weakly bound to the surface of the material. After a longe r reaction period, some deposits appear that are strongly bound to the surf ace. At higher temperatures, a fraction of the coke migrates out of the por es. Then, part of the coke (most likely aliphatics) desorbs and moves away, while the other part (presumably aromatics) adsorbs on the external surfac e of the sieve. The coke remaining both in the pores and on the external su rface mostly forms multilayered polyaromatic structures that are strongly b ound to the surface of the material. The water sorption capacity of the stu died materials decreases with the content of the deposits.