EVALUATION OF COMMERCIAL FCC CATALYSTS FOR HYDROCARBON CONVERSION I -PHYSICOCHEMICAL CHARACTERIZATION AND N-HEXANE CONVERSION

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 cou ld be fully explained by three reaction pathways: protolytic cracking, protolytic dehydrogenation and hydride transfer. Matrix components di d not contribute to the n-hexane conversion. A correlation of the acid strength distribution, measured by pyridine TPD showed that nearly al l sites with high acid strength are located in the micropores of the z eolite component. Al-27-MAS-NMR distinction between octahedral-, tetra hedral- and pentacoordinated species seems to be unsuitable for the de termination of different tetrahedral species in this kind of catalysts . The introduction of rare-earth metals into the zeolites increases th e acid strength of the active sites manifested in sequential reactions of the primary formed alkyl surface species, i.e. beta-scission and h ydride-transfer reactions. The addition of water to the reactant strea m decreases the conversion due to competitive adsorption, but does not change the amount, nor the nature of the active site. (C) 1998 Elsevi er Science B.V.