Probing the active sites of aluminated mesoporous molecular sieve MCM-41 by secondary synthesis in the conversion of cyclohexanol

Salasiah Endud, University Technology Malaysia
Hadi Nur, University Technology Malaysia
Halimaton Hamdan, University Technology Malaysia

Abstract

The active sites of H-Al-MCM41 aluminated by secondary synthesis have been probed by the conversion of cyclohexanol and compared with those of H-Al-MCM-41 prepared by direct synthesis, purely silceous MCM-41, AlPO4-5 and HZM-5. Conversion of cyclohexanol produces cyclohexene, cyclohexanone and 3-methylpentane in the presence of Bronsted, basic and Lewis acid sites respectively, whereas cyclohexanol is converted to polyaromatic compounds in the presence of very strong acid sites as those found in H-ZSM-5. The formation cyclohexene as the only product of conversion over H-Al-MCM-41 prepared by direct and secondary synthesis indicates the presence of Bronsted acid sites in both systems, which is not observed in the purely sliceous MCM-41 and AlPO4-5 samples. The larger amount of cyclohexanone formed over H-Al-MCM-41 by secondary synthesis suggests that there is a highre degree of Bronsted acidity in this system than that of H-Al-MCM-41 by secondary synthesis. However the strength of acidity in H-Al-MCM-41 by secondary synthesis is a weaker than that of HZSM-5. In addition, the results of this reaction, suppoted by IR spectroscopy study, do not indicate the presence of Lewis acidity in H-Al-MCM-41 prepared by secondary synthesis.