EFFECT OF ZEOLITE CRYSTALLITE SIZE ON Pt/KL CATALYSTS USED FOR THE AROMATIZATION OF n-OCTANE

Abstract

The effects of varying zeolite crystallite size in n-octane aromatization over Pt/KL have been studied on a series of catalysts. Various KL zeolites were synthesized via microwave-hydrothermal treatment, which allows for good control of crystallite morphology. Zeolites with different crystallite sizes were prepared by varying aging time (17–24 h), amount of barium (0–445 ppm), and seeding (0–8 wt%). The results showed that higher aging time resulted in smaller zeolite crystallite size, whereas the addition of barium resulted in larger crystallite size. Moreover, the addition of seeding reduced the crystallite size from 1.47 to 0.94 μm. Pt supported on different zeolite catalysts (Pt/KL) was prepared by vapor phase impregnation (VPI). The fresh catalysts were characterized by DRIFTS of adsorbed CO and volumetric hydrogen chemisorption. The results indicated that Pt clusters are well dispersed inside the zeolite channel in all the catalysts prepared. The aromatization of n-octane was tested on the different catalysts at 500°C and atmospheric pressure. It was found that the catalytic activity of all catalysts dropped rapidly after about 200 min on stream due to coke plugging inside the pore of the KL zeolite. It was also observed that less ethylbenzene (EB) and o-xylene (OX) were obtained as the conversion increased because both EB and OX are converted to smaller molecules such as benzene, toluene, etc., by secondary hydrogenolysis. Furthermore, the EB/OX ratio increases with zeolite crystallite size due to an enhanced preferential conversion of the larger OX molecules compared to the narrower EB as their path through the pores is restricted.

Keywords:

• Microwave-hydrothermal treatment technique
• n-Octane aromatization
• Zeolite

Acknowledgment

This work was supported by the Thailand Research Fund (TRF), the Petroleum and Petrochemical Technology Consortium (PPT) through CU-PPC of the Petroleum and Petrochemical College, Chulalongkorn University, and Ratchadapiseksomphot Endowment Fund of Chulalongkorn University. We gratefully acknowledge the Oklahoma Center for Advancement of Science and Technology (OCAST) for providing financial support of the work accomplished at the University of Oklahoma.

Notes

*Axx represents aging time of xx h, Cxx represents crystallization time of h, Bx represents the amount of barium with 115, 230, and 345 ppm, where x = 1, 2, and 3, respectively, and Sx represents the seeding used of x wt%.

**Synthesized by using conventional hydrothermal treatment.