Catalytic Cracking of n-Dodecane over P-Modified MFI Zeolites Synthesized by Steam-Assisted Conversion: Effect of SiO₂/Al₂O₃ Ratio

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with different SiO₂/Al₂O₃ ratios synthesized by steam-assisted crystallization (SAC) and modified with phosphorus (4 wt % loading). Their physicochemical properties were characterized by X-ray diffraction analysis, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, ammonia temperature-programmed desorption, and MAS NMR spectroscopy. Both the parent and P-modified MFI zeolites were then subjected to catalytic tests in cracking of n-dodecane. The yield of light olefins was enhanced only in two cases: when MFI zeolites with SiO₂/Al₂O₃ ratios of 30–70 were modified with 4 wt % phosphorus and when parent MFI zeolites with SiO₂/Al₂O₃ ratios of 100–220 were used. It was further found that, in terms of catalytic performance in the cracking of n-dodecane, the MFI zeolites synthesized by SAC were comparable to a commercially available MFI zeolite synthesized under hydrothermal conditions. Moreover, in contrast to the commercially available zeolite, phosphorus modification of the SAC-synthesized zeolite enhanced the yield of C₂–C₄ olefins.