Mechanistic insights into coke suppression and enhanced olefin selectivity in mixed metal oxide-modified SAPO-34 for high-performance methanol-to-olefins catalysis
Armin Abbasi, Jafar Towfighi Darian, Mahdi Pourmand, Masoud Safari Yazd
Abstract
• Higher olefin selectivity : SPM achieves 85.7 % total olefin selectivity, surpassing SP (76.6 %). • Extended catalyst lifespan : SPM maintains stability nearly twice as long as SP. • Optimized propylene yield : SPM enhances P/E ratio (2.9 vs. 1.5 in SP). • Improved porosity and acidity : Enhanced mass transfer reduces coke formation. • Effective coke suppression : MD simulations confirm reduced coke precursor formation and promoted coke oxidation. The methanol-to-olefins (MTO) process is a key catalytic route for light olefin production, yet challenges related to catalyst deactivation and coke formation persist. In this study, we investigate the catalytic performance of SAPO-34 (SP) and a modified SAPO-34 catalyst incorporating a mixed metal oxide of indium oxide and cerium oxide (SPM) to enhance selectivity, stability, and coke resistance. A combination of experimental and theoretical approaches, including catalyst characterization, MTO catalytic testing, and molecular dynamics (MD) simulations, was employed to elucidate the impact of mixed metal oxide incorporation on catalyst properties. The results indicate that SPM exhibits significantly higher total olefin selectivity (85.7 %) compared to SP (76.6 %), with improved stability and a catalytic lifetime approximately twice as long. Furthermore, SPM demonstrates a higher propylene-to-ethylene (P/E) ratio, reaching 2.9 at the initial stage compared to 1.5 for SP. The incorporation of mixed metal oxides enhances mesoporosity and modifies acid site distribution, reducing excessive secondary reactions and mitigating coke formation. MD simulations confirm that SPM inhibits the formation of formaldehyde species, a key coke precursor, while promoting coke oxidation, thereby extending catalyst lifespan. These findings suggest that mixed metal oxide incorporation is an effective strategy for optimizing SAPO-34-based catalysts for sustainable MTO applications.