Mechanistic Aspects of n-Paraffins Hydrocracking: Influence of Zeolite Morphology and Acidity of Pd(Pt)/ZSM-5 Catalysts: Influence of zeolite morphology and acidity of Pd(Pt)/ZSM-5 catalysts

The influence of zeolite domain size, acidity, and metal type on n-decane and n-nonadecane hydroconversion was investigated for bifunctional Pd(Pt)/ZSM-5 zeolite (bulk, desilicated, thin and thick nanosheets). Decreasing the size of zeolitic domains to a few nanometers results in lower overall activity, higher skeletal isomerization yield, and an imbalance between metal and acid functions. These changes are attributed to a lower pore occupancy of olefinic intermediates due to the substantially larger external surface of nanosheets and higher desorption rates. Well-balanced bifunctional behavior and higher activity of nanosheet ZSM-5 can be achieved by strengthening the metal function or lowering the acidity. The influence on the isomerized and cracked product fractions is also discussed. Hydroconversion of n-nonadecane gave low yields of skeletal isomers over all Pd-loaded ZSM-5 catalysts and led to significant over-cracking due to the long intracrystalline residence times of the long hydrocarbon reactant.