Effects of ZSM-5 Modification with Manganese and Iron Cations on n-Dodecane/2-Methylthiophene Conversion Pathway

This study investigates the effects of modifying ZSM-5 zeolites with iron and manganese via ion exchange. It focuses on how this modification alters the physicochemical properties of the zeolites and influences the conversion pathway of a n-dodecane/2-methylthiophene (5000 ppm S) feedstock in catalytic cracking. For all modified zeolites, which had SiO2/Al2O3 ratios of 23 and 80 and metal loadings up to 1.94 wt %, the decrease in micropore volume and specific surface area did not exceed the margin of error. The modification of ZSM-5 with either Fe or Mn led to significant improvements, with the SiO2/Al2O3 playing a key role. Acidity, confirmed by NH3-TPD measurements and quantum-chemical (DFT) simulations, increased in concentration (by 89%) and strength for the zeolite with SiO2/Al2O3 = 23. Catalytic performance was enhanced with both modifier metals and for both zeolites, but more profoundly for the SiO2/Al2O3 = 23 variant: the yield of light olefins increased by 45% (compared to 26% for the SiO2/Al2O3 = 80 zeolite), while the sulfur content in liquid products was reduced by 46% (compared to 33%).