Comparative study of naphtha cracking over SAPO-34 and HZSM-5: Effects of cerium and zirconium on the catalytic performance

Thermal catalytic cracking of naphtha over 2 wt% cerium and/or zirconium modified SAPO-34 and HZSM-5 catalysts was investigated. XRD patterns of probed catalysts demonstrated that structure of SAPO-34 and HZSM-5 remained intact in the presence of cerium and/or zirconium. Measurement of the acidity with NH3-TPD showed that the density of weak, middle and strong acid sites was higher in SAPO-34 compared to HZSM-5. The middle and strong acid sites of both catalysts increased after modification. The yield of propylene (26.23 wt%) was higher in HZSM-5 catalyst whereas SAPO-34 produced more ethylene (17.05 wt%). The yield of ethylene and propylene on SAPO-34 boosted in the following order: Ce–Zr/SAPO-34 > Ce/SAPO-34 > Zr/SAPO-34 > SAPO-34, which was synchronized with middle and strong acid sites concentration. The yield of ethylene and propylene on HZSM-5 increased after modification with cerium and zirconium and attained to 14.96 wt% and 34.32 wt%, respectively. Deactivation tests were carried out during 8 h time-on-stream over SAPO-34, Ce–Zr/SAPO-34, HZSM-5 and Ce–Zr/HZSM-5 catalysts. HZSM-5 exhibited superior performance compared to SAPO-34 and results showed lifetime amelioration after modification of both catalysts with cerium and zirconium.