Incorporation of mono and bimetallic MnNi into SAPO-34 framework used in conversion of methanol to ethylene and propylene: Alteration of acidic properties and catalytic performance

Nanostructured MeAPSO-34 (MeMn, Ni, and MnNi) catalysts were synthesized by hydrothermal method using diethylamine (DEA) as template. The influence of Ni, Mn, and MnNi metal ions incorporation into the SAPO-34 framework was investigated on its physicochemical properties and catalytic performance towards methanol to light olefins. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, particle size distribution, energy dispersive X-ray, Brunner-Emmett-Teller, Fourier transform infrared, UV-vis spectroscopy, and temperature-programmed desorption of ammonia techniques. The results of X-ray diffraction patterns revealed that various metals, based on their unique characteristics, play different roles in the crystallization of SAPO-34 crystalline phase. The energy dispersive X-ray micrographs indicated appropriate distribution of Mn metal ions in comparison with Ni modifier. The catalytic performance of these catalysts showed that the type of metal ions has low effect on methanol conversion, whereas it has considerable effect on stability and products selectivity. The stability of MnAPSO-34 catalyst is much higher than the others. The selectivity of olefins for this sample with a high specific surface area and proper distribution of strong/weak acid sites was about 98% after 10 hr. The main steps of metal ions incorporation into the SAPO-34 framework and a possible reaction mechanism for methanol to light olefins process were discussed in details.