Surface potential charge modulation and sequential etching strategies for optimizing SAPO-34 catalysts in the MTO process: Mechanistic insights into catalytic performance

The methanol-to-olefins (MTO) process over SAPO-34 catalysts is significantly influenced by surface potential charge, affecting methanol adsorption, intermediate spillover, and coke formation. This study investigates the catalytic performance and mechanistic behavior of SAPO-34 catalysts modified through acidic (SP34-A), basic (SP34-B), and sequential acid-base (SP34-AB) etching, with the unmodified SAPO-34 (SP34-P) serving as a reference. The impact of surface potential charge on catalyst performance was examined using molecular dynamics (MD) simulations, NH₃-TPD acidity measurements, and zeta potential analysis. The results reveal that a highly negative surface charge (SP34-A, −67 mV) intensifies methanol adsorption but limits spillover efficiency, promoting formaldehyde accumulation and increasing coke deposition, ultimately reducing catalyst lifetime. In contrast, a positive surface charge (SP34-B, +22 mV) enhances spillover and moderates adsorption strength, reducing coke formation and extending catalyst stability. The sequential acid-base etched catalyst (SP34-AB, +16.9 mV) achieves a well-balanced surface charge, optimizing methanol adsorption, spillover behavior, and diffusion efficiency. This balance minimizes secondary reactions, extends catalyst lifetime (586 min, 1.63 times longer than SP34-P), and improves light olefin selectivity (88.82 %), demonstrating the superior catalytic performance of SP34-AB. Structural and textural analysis further confirms that hierarchical porosity, induced via sequential etching, enhances mass transfer and mitigates diffusion limitations, preventing excessive coke formation. These findings establish surface potential charge as a critical parameter in SAPO-34 catalyst design, highlighting sequential acid-base etching as an effective modification strategy to enhance MTO efficiency and catalyst longevity.