Evaluation of commercial FCC catalysts for hydrocarbon conversion: I. Physicochemical characterization and n-hexane conversion Original Research Article

The physicochemical properties of six steam-stabilized, commercial FCC catalysts were compared in respect of their catalytic activity for n-hexane conversion. The conversion of n-hexane over these catalysts could be fully explained by three reaction pathways: protolytic cracking, protolytic dehydrogenation and hydride transfer. Matrix components did not contribute to the n-hexane conversion. A correlation of the acid strength distribution, measured by pyridine TPD showed that nearly all sites with high acid strength are located in the micropores of the zeolite component. 27Al–MAS–NMR distinction between octahedral-, tetrahedral- and pentacoordinated species seems to be unsuitable for the determination of different tetrahedral species in this kind of catalysts. The introduction of rare-earth metals into the zeolites increases the acid strength of the active sites manifested in sequential reactions of the primary formed alkyl surface species, i.e. β-scission and hydride-transfer reactions. The addition of water to the reactant stream decreases the conversion due to competitive adsorption, but does not change the amount, nor the nature of the active site.