SAPO-34 Zeolite Nanocrystals Coated with ZrO₂ as Catalysts for Methanol-to-Olefin Conversion

The methanol-to-olefin reactions over SAPO-34 zeolites have been fascinating since the selectivity for valuable light olefins is high. However, the catalyst lifetime is very short due to rapid formation of coke on SAPO-34. Herein, we propose a method to coat the external surface of SAPO-34 nanocrystals with crystalline ZrO2 derived from UiO-66, Zr-based metal–organic frameworks (MOFs), that inhibits coke formation. Powder X-ray diffraction and transmission electron microscopy images implied that the crystalline ZrO2 was accumulated on the external surface of SAPO-34 without any deformation of the crystal structure of SAPO-34. In addition, FTIR spectroscopy using pyridine as a probe molecule indicated that the ZrO2-coated SAPO-34 had no Brønsted acidity on its external surface. The ZrO2-coated SAPO-34 showed a longer catalytic lifetime than unmodified SAPO-34. The absence of acidity on the external surface of the ZrO2-coated SAPO-34 is likely to contribute to the suppression of coke formation on the pore mouths of SAPO-34. This work provides a strategy for the surface modification toward porous nanomaterials including zeolites and MOFs.