Synthesis of hierarchical SAPO-34 catalysts modified with manganese nanoparticles for conversion of methanol to light olefins: a deactivation and regeneration study

The hierarchical type 34 silicoaluminophosphate (SAPO-34) catalysts containing manganese were synthesized in the presence of carbon nanotube as mesopore template and tested in the transformation of methanol to light olefin. Also, the regenerability of spent catalysts after methanol to olefins (MTO) reaction was studied. In order to investigate the effect of manganese on the framework and extra framework of SAPO-34 structure, manganese species were added to SAPO-34 by isomorphous substitution and impregnation methods. The physicochemical properties of modified hierarchical samples such as crystallinity, acidity, porosity and reducibility were strongly dependent on the metal addition method. The modified hierarchical samples showed superior performance in the terms of activity and longevity compared to unmodified hierarchical SAPO-34. Among the samples, hierarchical MnAPSO-34 catalyst prepared by isomorphous substitution exhibited the best performance in the MTO reaction. The characterization of the used hierarchical catalysts by TGA analysis revealed that the deposited coke on modified samples was lower compared to unmodified hierarchical SAPO-34. The regenerated modified hierarchical SAPO-34 samples showed more enhanced ethylene selectivity in the MTO reaction and longer lifetime due to the existence of more methylated naphthalenes and methylated benzenes in the residual coke after regeneration.