Metal-substituted sponge-like MFI zeolites as high-performance catalysts for selective conversion of methanol to propylene

In this study, sponge-like and M-substituted (M: Mn, W and Ce) sponge-like MFI zeolites were successfully synthesized by seed-assisted hydrothermal technique. The special bi-functional organic surfactant of C22-6-6Br2 with multi-ammonium groups was separately synthesized and used as structure directing agent (SDA). The prepared catalyst samples were examined in methanol to propylene (MTP) process and demonstrated superior catalytic performance compared to conventional H-ZSM-5 and M-substituted MFI zeolite nanosheets. The W-substituted sponge-like MFI zeolite effectively showed the most enhanced catalytic activity with complete methanol conversion, propylene selectivity of 56.3%, total selectivity of light olefins of 88.3% and catalytic life-span of 161 h. Moreover, to increase propylene selectivity, bi-metallic and trTmetallic sponge-like MFI zeolites were successfully synthesized via seed-assisted hydrothermal method by utilizing central composite design (CCD) strategy. For optimizing promoter compositions in lattice of bi-metallic and tri-metallic sponge-like MFI zeolites, the incorporated response surface methodology (RSM)-CCD technique and also an intelligent approach namely neuro-genetic method were applied. It was deduced that optimal bi-metallic sponge-like MFI zeolite suggested by neuro-genetic approach approved the highest propylene selectivity (66.7%). Synthesized catalysts were appropriately characterized by XRD, FE-SEM, EDX, TEM, FT-IR, N-2 adsorption/desorption and NH3-TPD analyses which comparatively approved high specific surface area and dominant meso-porosity.