A novel synthesis of highly active and highly stable non-noble-nickel-modified persulfated Al₂O₃@ZrO₂ core-shell catalysts for n-pentane isomerization

The non-noble metal modified sulfated zirconia was found easy to deactivate. Herein, highly active and highly stable non-noble core-shell Ni-S₂O₈²⁻/Al₂O₃@ZrO₂ catalysts (Ni-SA@Z-x, x = Al content in wt%) have been successfully prepared and investigated for n-pentane isomerization. The results showed that the core-shell Ni-SA@Z-30 provided a sustained high isopentane yield (63.1%) with little or no deactivation within 5000 min at a mild reaction pressure of 2.0 MPa, which can be attributed to the following factors: (ⅰ) carbon deposition was greatly suppressed by the large pore size and huge pore volume; (ⅱ) the loss of sulfur entities was suppressed because the small and highly dispersed tetragonal ZrO₂ particles can bond with the S species strongly; (ⅲ) strong Brønsted acidity can be maintained well after the isomerization. The pore structures and acid nature of the core-shell Ni-SA@Z-x are entirely different from those of the normal structure Ni-S₂O₈²⁻/ZrO_2-Al₂O₃, even though the Al content and the compositions of the individual components are the same. The Al₂O₃ cores endow the catalysts with high internal surface area and high mechanical strength. Meanwhile, the ZrO₂ shell, which consists of more and smaller tetragonal ZrO₂ particles because of the large surface area of the Al₂O₃ core, promotes the formation of more stable sulfur species and stronger binding sites.