Synthesis, characterization and nhexane catalytic cracking activity of zinc-substituted aluminophosphate molecular sieves (ZnAPO-5)

Zinc-substituted aluminophosphate molecular sieves (ZnAPO-5, AFI topology) containing different zinc contents were synthesized by static hydrothermal method, using triethylamine as an organic template agent. The as-synthesized ZnAPO-5 molecular sieves were characterized by XRD, SEM, N2-adsorption, MAS-NMR and ICP-AES techniques. Experimental data indicate that Zn as a heteroatom was successfully incorporated into the framework of AlPO4-5. The resultant ZnAPO-5 molecular sieves with regular hexagonal prism morphology are of high crystallinity and purity. The n-hexane cracking over ZnAPO-5 was examined under different reaction conditions. It is found that ZnAPO-5 molecular sieves exhibit a moderate activity for the n-hexane cracking conversion in the temperature range of 723K~823K. The cracking results obtained show that the conversion level of n-hexane increased with increasing reaction temperature and contact time, and that the first order was determined in the nhexane concentration. Relations between rates and reaction temperature can be expressed in terms of Arrhenius formula in the whole temperature range. Based on the kinetic data and product distributions, monomolecular protolytic mechanism was concluded to prevail under the reaction conditions applied.