Catalytic cracking of n-octane on small-pore zeolites

The small-pore zeolites Alpha (LTA), chabazite (CHA), NU-3 (LEV), Rho (RHO), Sigma-1 (DDR), ZK-5 (KFI) and ZSM-58 (DDR) were hydrothermally synthesized and characterized by XRD, elemental analysis, Al-27 MAS NMR spectroscopy and n-octane adsorption. The Bronsted acid forms of the zeolites were used as catalysts for cracking of n-octane in a continuously operated fixed-bed reactor. For comparison, n-octane cracking experiments were performed on the medium-pore zeolite H-ZSM-5 (MFI) and the large-pore zeolite H-Beta (*BEA). In agreement with prior work on catalytic cracking of short-chain n-alkanes, it was found that the contribution of monomolecular Haag-Dessau cracking increases, as the pores are getting narrower. However, if a long-chain n-alkane, such as n-octane, is used as reactant, the typical products of both monomolecular and bimolecular cracking are observed on all 8-ring zeolites. For various small-pore zeolites, a pronounced influence of the pore dimensions was observed. Selectivities to C-1 and C-2 products were shown to increase with decreasing size of the pore windows and increasing spatial constraints of the pore systems. (c) 2005 Elsevier Inc. All rights reserved.