Pd catalyst supported on SiO2–Al2O3 xerogel for hydrocracking of paraffin wax to middle distillate

SiO2–Al2O3 xerogel supports (SA-X) with different SiO2 contents (X, wt%) were prepared by a sol–gel method. Pd catalysts supported on SA-X (Pd/SA-X) were then prepared by an impregnation method for use in the production of middle distillate (C10–C20) through hydrocracking of paraffin wax. Acidity of Pd/SA-X catalysts determined by NH3-TPD experiments showed a volcano-shaped trend with respect to SiO2 content. Acidity of the catalyst played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax increased with increasing acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that optimal acidity of the catalyst was required for maximum production of middle distillate. Among the catalyst tested, Pd/SA-40 catalyst with moderate acidity showed the highest yield for middle distillate. It was also found that high Pd dispersion of Pd/SA-X catalyst led to the enhanced selectivity for middle distillate in the hydrocracking of paraffin wax.