Mg/Ca modified hierarchical porous ZSM-5 zeolite for light-olefins production from chloromethane

The hierarchical porous ZSM-5 zeolites modified by the metal Mg and Ca (MH-ZSM-5) were constructed for catalytic coupling of CH₃Cl to light-olefins (CMTO). The properties of the prepared catalysts were characterized by X-ray diffraction, N₂ adsorption–desorption, scanning electron microscopy, Fourier-transform infrared spectroscopy and NH₃ temperature-programmed desorption measurements. Results showed that the organosilane treatment could obviously change the morphology of ZSM-5 zeolites from cubic to sphere and introduce more mesoporous, and the metal modification could significantly reduce the amount of Brønsted acid. The mesoporous structure was in favor of mass transfer to avoid carbon deposits to prolong the lifetime of catalysts. In addition, the fewer strong acid sites could suppress the occurrence of side reactions to improve the selectivity of light olefins. Therefore, MH-ZSM-5 with the more mesoporous and appropriate acidity exhibited the best catalytic performance, among which the selectivity of light-olefins reached 90.9% and the lifetime (the duration of CH₃Cl conversion > 98%) was up to 72 h.