Hydroconversion of n-octane over different MoO₃ phase modified nanosized HZSM-5 zeolites

The n-octane hydroconversion catalysts were prepared by the impregnation of nanosized HZSM-5 with ammonium heptamolybdate or phosphomolybdic acid (PMA) precursors and were characterised by SEM, BET, FT-IR, UV–Vis, XRD, Py-IR and NH₃-TPD. The hydroconversion of n-octane over a little phosphorus doping on the n-octane hydroconversion activity of MoO₃/ZSM-5 catalysts has been investigated in order to obtain light isomers, alkanes and aromatic products with high octane number. In particular, the use of PMA increases the ability of aromatization and producing light iso-alkanes for nanosized HZSM-5 zeolites. The yield of total aromatics and i/n ratio over PMA-based MoO₃/ZSM-5 catalysts reached 31.7 and 3.3 after 10 h of continuous reaction, respectively. When 0.2 wt% of phosphorus is added to the catalyst prepared from heptamolybdate, the activity is suppressed. A mixture of monoclinic β-MoO₃ and orthorhombic α-MoO₃ favors increasing aromatization performance over nanosized HZSM-5 zeolites, and orthorhombic α-MoO₃ is beneficial to the production of light iso-alkanes. It could be attributed to the difference between orthorhombic α-MoO₃ and monoclinic β-MoO₃ as well as the structural dissimilarity between the two phases on nanosized HZSM-5 zeolites. The improved activity of n-octane hydroconversion over these catalysts and the mechanism of hydroconversion is discussed.