Textural Properties and Catalytic Applications of ZSM-5 Monolith Foam for Methanol Conversion

Abstract

ZSM-5 monolith foam (ZMF) samples with various framework Si/Al ratios have been successfully synthesized by polyurethane foam (PUF) template method and evaluated for their catalytic performance towards methanol to propylene (MTP) reaction. The samples were tested for their textural properties using SEM, XRD, BET surface area, pore volume and NH₃-TPD techniques revealing the formation of ZMF exhibiting about 100–300 μm range macro pores created by packed assembly of 5 μm size orthorhombic shaped ZSM-5 crystals. The ZMF samples exhibited effective activity in methanol to olefin conversion, with superior product selectivities at optimum Si/Al ratio of 250. Further, the ZMF catalyst with high macro porosity exhibited superior catalytic activity compared to its pelletized form, especially at higher feed flow rates, that signifies the importance of macro porous structure of ZMF in facilitating the enhanced mass transport for the labile diffusion of light olefins. Reaction temperature also played a vital role in determining product selectivity. At 500 °C, the catalysts exhibited the highest light olefin (C₂ ⁼–C₄ ⁼) selectivity and above this temperature, formation of C₅ ⁺ is prevailed at the cost of C₂ ⁼–C₄ ⁼ revealing the accelerated occurrence of oligomerization reactions at these conditions. At optimized catalytic properties and reaction conditions, the catalyst exhibited as high as 75% selectivity to C₂–C₄ olefins, with propylene as major component (~44%).