Impact of modified acidity and diffusion on ethylene-to-propylene reaction via size and shape controlled SSZ-13 zeolite

Abstract

The particle size of SSZ-13 zeolites, while maintaining a consistent cubic shape and uniform Si/Al₂ ratios, was successfully controlled from 100 nm to 900 nm via seed-assisted interzeolite conversion of Y zeolites in the presence of TMAdaOH and NaOH. Despite the consistent Si/Al₂ ratio, variations in particle size induced significant changes in acidic properties, attributed to alterations in the coordination of aluminum species on the zeolite surface. Specifically, smaller particle sizes and spherical morphology resulted in reduced acidity, particularly at the strong acid sites. Propane equilibrium isotherms also revealed that the modifications of particle size and the associated acidity substantially influence the diffusion and residence time of reactants and products. In ethylene-to-propylene (ETP) reactions, smaller particle sizes in cubic SSZ-13 enhanced diffusion and reduced acidity, minimizing undesirable successive reactions and increasing propylene selectivity. However, excessive diffusion and weaker acidity caused the premature escape of intermediates, demonstrating a volcano-type relationship between particle size and catalytic efficiency. Notably, 250 nm-cubic SSZ-13 achieved an optimal balance of diffusion and acidity via size and shape control, leading to slower deactivation, higher propylene selectivity, and greater propylene yield. These findings provide valuable insights into the interplay between morphological modifications, physicochemical properties, and catalytic performance, offering a foundation for advancing the design of catalytic materials.