Fabrication of active, stable, and regenerable catalysts is the main purpose of researchers in which spinel-type catalysts can provide some excellent properties to utilize in chemical processes. However, some effective parameters on their properties and performance must be deeply evaluated. herefore, in this study, the effect of Ni/Al ratio on the properties and performance of Ni-NiAl 2 O 4 catalyst synthesized by solution combustion method was investigated. The sulfated structure of the samples was used as solid acid catalysts for the esterification of oleic acid. Various characterization techniques were carried out on SO42−/Ni-NiAl2O4 composites, and the results revealed that the increase of nickel concentration led to the formation of NiO and metal Ni which bonded strongly with sulfate groups during the impregnation process. The strong bands between Ni cations and sulfate group increase sharply the surface area (from 28.6 m2s−1 for Ni/Al ratio = 1 to 35.4 m 2 s −1 for Ni/Al ratio = 1.75) and the activity of the samples, consequently. However, higher amounts of Ni cations (Ni/Al ratio of 2) led to agglomerated particles that were detected on the surface which filled the porosities. It can cause to reduce the surface area and activity of SO 4 /Ni-NiAl 2 O 4 nanocatalyst. The sample fabricated by 1.75 times of Ni/Al ratio presented the highest surface area, pore diameter (the most of pores are greater than 8 nm), less roughness and uniform particle size that converted more than 95% of oleic acid to ester at the conditions of 120 °C, 9 molar ratio of methanol to oleic acid, 3 wt% of catalyst and 4 h of reaction time. It was also remained active for four uses and was successfully regenerated after deactivation by reloading the sulfate group.

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