The effect of Fe, P and Si/Al molar ratio on stability of HZSM-5 catalyst in naphtha thermal-catalytic cracking to light olefins

To investigate the effect of Si/Al ratio, Fe and P loadings on the stability of HZSM-5 in the catalytic cracking of naphtha, experimental tests were done over 20 h time on stream on modified HZSM-5 with different Si/Al molar ratios. NH3-TPD and TPO analyses showed that the more number of weak acid sites, the greater amount of coke is formed. According to TPO and XRD results, it was demonstrated that dealumination had a significant role in catalytic stability. Among catalysts, Fe(6)-P(2)/HZSM-5(25) showed the highest catalytic stability (1.86 wt.% propylene reduction).

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► HZSM-5 with lowest Si/Al ratio, moderate Fe and highest P shows highest stability.
► Framework Al can be stabilized by suitable amount of P by considering Si/Al ratio.
► Weak acidity leads to coke formation while strong acidity leads to propylene yield.