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 29Si NMR and N2 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.