Fluid catalytic cracking (FCC) is one of the most dominant processes for heavy feedstock conversion. By using ReaxFF dynamic simulations, the catalytic pyrolysis of hexadecane was investigated with the presence of ZSM-5, hydrated ZSM-5, and hydrated Al/ZSM-5 catalysts under high temperatures. Multimolecular simulation results showed that the hydrated ZSM-5 catalyst has good catalytic reactivity at higher temperatures, and the surface hydroxyl group could promote the yield of ethylene. The hydrated Al/ZSM-5 catalyst was more suitable for the production of small molecules under lower temperatures, and the introduction of aluminum would increase the yield of C-3 similar to C-4 and prevent the formation of C-O bonds. The unimolecular simulations confirmed that the introduction of aluminum in the hydrated Al/ZSM-5 catalyst would be beneficial to the dehydrogenation of reactant molecules. Thermal stability simulations of catalysts revealed that the introduction of aluminum into the ZSM-5 catalyst could stabilize the Si-O structure and inhibit the formation of a C-O bond.