Ni catalyst on ZSM-22 nanofibers bundles with good catalytic performance in the hydroisomerization of n-dodecane

Abstract

Developing non-noble catalyst with high performance is significant in the hydroisomerization of long-chain n-alkane to iso-alkanes. In this study, nanofiber-bundled ZSM-22 without any additives was successfully synthesized and used to prepare Ni catalyst (Ni/NB-HZSM-22, Ni loading 1.0 wt%) for hydroisomerization of n-dodecane (n-C12). The obtained Ni/NB-HZSM-22 catalyst exhibited much higher intrinsic catalytic activity (TOF = 0.077 s−1) than a conventional needle-shaped ZSM-22 supported Ni catalyst (Ni/C-HZSM-22, 0.026 s−1), especially higher isomerization selectivity (TOFiso, 0.071 s−1) than the Ni/C-HZSM-22 catalyst (0.021 s−1). Additionally, the Ni/NB-HZSM-22 catalyst had lower cracking/iso-dodecanes (iso-C12, 0.08) and di-branched/mono-branched (0) ratios than the Ni/C-HZSM-22 catalyst (0.25 and 0.07) after extrapolation of the n-C12 conversion to zero. This is mainly attributed to the nanofiber–bundled NB-HZSM-22 with well-crystallized structures and suitable acidity, leading to good synergistic catalysis between metal and acidic function for the Ni/NB-HZSM-22 catalyst. Although the Ni catalyst on the parent NB-ZSM-22 was less active, it had a similar optimal iso-C12 yield compared to the Ni/NB-HZSM-22 catalyst. In addition, the Ni/NB-HZSM-22 catalyst showed a maximum iso-C12 yield of 74.8%, which was much better than the Ni/C-HZSM-22 catalyst (58.7%), and showed comparable performance to a Pt catalyst on the NB-HZSM-22 (76.7%). These results suggested that the Ni catalyst on the NB-HZSM-22 was a promising candidate for the hydroisomerization catalyst.