Production of Middle Distillate Through Hydrocracking of Paraffin Wax over NiMo/SiO2–Al2O3 Catalysts: Effect of SiO2–Al2O3 Composition on Acid Property and Catalytic Performance of NiMo/SiO2–Al2O3 Catalysts

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SiO2–Al2O3 supports with different composition were prepared by a precipitation method in order to control the acid property of SiO2–Al2O3 supports. NiMo/SiO2–Al2O3 catalysts were then prepared by an impregnation method and sulfided for use in the production of middle distillate through hydrocracking of paraffin wax. It was revealed that MoS2 phase was dominantly formed in the NiMo/SiO2–Al2O3 catalysts, while Ni–Mo–S phase was not detected due to its fine dispersion. Acidity of NiMo/SiO2–Al2O3 catalysts measured by NH3–TPD experiments showed a volcano-shaped curve with respect to SiO2 content. Acidity of the catalysts played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax was monotonically increased with increasing acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. Thus, optimal acidity of NiMo/SiO2–Al2O3 catalysts was required for the maximum production of middle distillate through hydrocracking of paraffin wax.