Catalysts were degassed under vacuum at 160 °C for 5 h, and then, the sur­face area of catalysts was measured using a surface analyzer. The pore size distributions and pore volume were determined. Scanning electron microscope (SEM) was used for determination of surface morphology and shape of catalyst particles.

Collector

Furnace

I hermocouplc

Fig. 1 Schematic diagram of experimental apparatus

1.3 Preparation of ZSM-5 and SBA-15 Catalysts

The catalysts were activated by calcination at 420 °C in nitrogen for 1 h, cooled to 350 °C, and then calcined further in air at 540 °C for 12 h. After this, the catalysts were crushed into powder. Both polyethylene and catalyst powder were sieved to ensure that particle sizes remained around 60-150 mesh and then blended by grind­ing the desired amount of catalyst and polyethylene according to a certain ratio.