Enhanced light olefins production via n-pentane cracking using modified MFI catalysts

n-pentane catalytic cracking was studied over a series of MFI zeolites with varying SiO₂/Al₂O₃ ratios (30, 80, 280, 500, and 1500) using a fixed-bed reactor operated at temperature 550-650 °C. Other MFI zeolites (SiO₂/Al₂O₃ = 280) with various crystal morphology and size (such as large crystal and nano size) were also synthesized and tested for n-pentane cracking. The effects of MFI zeolite modification with ammonia and phosphorus on its physiochemical properties and catalytic activity were investigated. Among the parent MFI zeolites, MFI (280) demonstrated high selectivity (51%) towards light olefins (C₃ ⁼/C₂ ⁼ = 0.7) at 650 °C with undesired C₁-C₄ alkanes (38%). Surface modified MFI (280) zeolites of different crystal size and morphology showed improvement towards propylene selectivity by suppressing undesired reactions. Phosphorous-modified MFI zeolite with a large crystal size was found to improve light olefin selectivity (52.2%) with C₃ ⁼/C₂ ⁼ = ∼1.3 and reduce undesired C₁-C₄ alkanes (8%) formation due to suppressed strong acidic sites. The characterization and evaluation results for the modified MFI (280) revealed that the incorporation of phosphorous created moderate acidic sites, which were stabilized by some non-framework aluminum species, thereby leading to suppressing the formation of undesired C₁-C₄ alkanes with improved light olefins selectivity.