Production of middle distillate through hydrocracking of paraffin wax over Pd/SiO2–Al2O3 catalysts

Pd/SiO2–Al2O3 catalysts (Pd/SA-X) with different SiO2 contents (X, wt%) were prepared for use in the production of middle distillate (C10–C20) through hydrocracking of paraffin wax. The effect of SiO2 content of Pd/SA-X catalysts on their physicochemical properties and catalytic performance in the hydrocracking of paraffin wax was investigated. High surface area and well-developed mesopores of Pd/SA-X catalysts improved the dispersion of Pd species on the SiO2–Al2O3 support. Acidity of Pd/SA-X catalysts determined by NH3-TPD experiments showed a volcano-shaped trend with respect to SiO2 content. Conversion of paraffin wax increased with increasing acidity of the catalyst, while selectivity for middle distillate decreased with increasing acidity of the catalyst. Yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that acidity of Pd/SA-X catalysts played an important role in determining the catalytic performance in the hydrocraking of paraffin wax. Among the catalyst tested, Pd/SA-69 with moderate acidity showed the highest yield for middle distillate.