Influence of various aluminum distributions on modification of ZSM-5 zeolite framework with cobalt ions in alkane catalytic cracking

HZSM-5 (HZ(1) and HZ(2)) zeolites synthesized with various framework aluminum distributions and also cobalt-modified H-form zeolites (Co/HZ(1) and Co/HZ(2)) were used to evaluate the production of light olefins in catalytic cracking of liquefied petroleum gas (LPG). The characterization of catalysts was carried out by X-ray diffraction (XRD), field-emission scanning electron microscopic (FE-SEM), Brunauer-Emmett-Teller (BET), X-ray fluorescence (XRF), Barrett-Joyner-Halenda (BJH), Thermal Gravimetric Analyzer (TGA), diffuse reflectance (DR) UV-visible and NH3-Temperature-Programmed Desorption (NH3-TPD) analyses. The results showed that the highest single aluminum proportion was 89.3% for NaZSM-5(1) synthesized with aluminum nitrate. The catalytic results indicated that the olefin yield increased from 30.8% to 39.3% and 24.7% to 41.4% after HZ(1) and HZ(2) modification with cobalt ions, respectively. After 240min of time on stream (TOS), the olefin yield decreased 33.92, 23.37, 48.24 and 21.39% for HZ(1), Co/HZ(1), HZ(2) and Co/HZ(2), respectively. The amount of coke deposited on catalyst decreased from 15.28% to 4.97% after modification of HZ(2). The highest stability and the highest ratio of propylene to ethylene (P/E) was found for Co/HZ(2). Consequently, the effect of HZ(2) (with higher close Al atoms) modification with cobalt ions on the olefin production and catalytic stability was greater than HZ(1) modification.