Hydroisomerization of n-octane over nickel-tungsten supported on silica-alumina catalysts

The hydroisomerization of n-octane over Ni-WOx/silica-alumina based catalysts has been investigated in a down flow fixed-bed quartz reactor by changing operating conditions such as time on stream, reaction temperature, SiO2/Al2O3 and H-2/n-octane ratio, andspace velocity. This study aims to understand the activity and selectivity properties of the prepared catalysts and to analyze the relationship between the metal content, the acidity (nature and strength) of the samples, and the main reaction paths. It was found that all catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. On increasing the nickel loading, conversion increases as does selectivity to isomerization, which reaches a maximum and then decreases. Moreover, the obtained results showed that the H-2 partial pressure and SiO2/Al2O3 ratio positively affect isomerization selectivity while the opposite effect was observed for activity (conversion). In addition, the main reaction pathways in n-octane hydroconversion over the prepared solids were found to be isomerization, cracking, and hydrogenolysis. At steady-state conditions (after 100 min TOS), the catalyst with 15% of nickel and 10% of tungsten (WT(15,10)) showed the best results (69% of selectivity at 32.5% conversion).