Abstrakt

Characterization and cracking activity of MoO3-SiO2 catalysts

F.Sh.Mohamed, M.R.Mostafa

Pure silica and a series of MoO3/SiO2 catalysts with different MoO3 loadings( 2-16wt%) were prepared using the standard incipient wetness technique. The catalysts were characterized using XRD and FTIR techniques. The textural properties were determined from nitrogen adsorption at 77K. the acidic properties of these catalysts were measured by the amine titration method. The cracking of cumene was investigated over these catalysts. XRD data revealed the amorphous nature of the catalyst up to 6 wt%MoO3 loading and the formation of crystalline MoO3 phase on amorphous silica support were detected only for the catalyst with higherMoO3 loading. Loading SiO2 with higherMoO3 (9wt%) leads to a significant change in texture, surface acidity and catalytic activity of the prepared catalysts. Catalysts with higher MoO3 loading showmuch higher acid strength compared to the catalysts with lowerMoO3 loading(6 wt%). The cracking activity has been related to the strength of the acid sites presented on the catalyst surface. Cracking of cumene over the investigated catalyst necessitates the presence of strong acid sites. These sites are evidently Bronsted acid sites on which the cracking process probably proceeds via a carbonium ion mechanism.