Controlling the SAPO-34 Particle Size to Enhance Reaction-Diffusion Behavior for Improving Catalytic Efficiency in the MTO Reaction

The SAPO-34 zeolite as an important catalyst is widely used in the methanol-to-olefin reaction, but understanding the internal diffusion behavior of its reactant methanol is still a challenge. In this work, a series of SAPO-34 catalysts with different particle sizes were prepared, among which the thin-layer SAPO-34 zeolite could be synthesized when the ratio of TEAOH/Mor is 8:1, which exhibits a high selectivity of 95% for light olefins and a long lifetime of 410 min. Through 29 Si NMR and N 2 physical adsorption–desorption, it indicates that more Si(4Al) coordination structures and a larger external volume jointly determine the stability of SAPO-34. Combining the TG and BET results of deactivated catalysts, it was found that the main reason for deactivation is the micropore blocked by coke deposition. The kinetic results demonstrated that the particle size of the zeolite is inversely proportional to its apparent reaction rate. The calculation of the Thiele modulus shows that the intramolecular diffusion rate of the small particle zeolite is faster. The catalytic efficiency can be enhanced by reducing the particle size due to the partly removed internal diffusion and the improved utilization of acid sites.