Hierarchical ZSM-5 synthesized from Bangka kaolin and Bayat natural zeolite for methane conversion catalysts

Abstract

Hierarchical ZSM-5 has been successfully synthesized from Bayat natural zeolite as alumina and silica source and Bangka kaolinite as an additional silica source using tetrapropylammonium hydroxide (TPAOH) and poly(acrylamide-co-dialyldimethylammonium chloride) (PDDA-M) as a structure and pore directing agent. XRD pattern shows an evidence of MFI (Mordenite Inverted Framework) structure with peaks at 2θ = 8.01°, 8.90° and 23.15°. SEM images show that the surface of as-synthesized zeolite has coffin-like structure, while EDX analysis shows it has a Si/Al molar ratio of 8.77. The N2 isotherm adsorption exhibited a type IV H4 curve, which indicated the material has mesoporosity, although the Barrett-Joyner-Halenda analysis showed the ZSM-5 has a pore size distribution around 1.937 nm, indicated the micropore dominating its pore size. This confirms that the as-synthesized natural ZSM-5 has hierarchical properties. This as-synthesized natural ZSM-5 then was impregnated with Fe2O3 to improve its catalytic activity towards methane conversion reaction. XRD analysis shows an existence of Fe2O3 at 2θ = 41.22°. Both Fe-impregnated synthetic and natural ZSM-5 show a higher percentage of methane conversion (84.825 % and 86.958 %, respectively), but they give a lower percentage yield of formaldehyde (39.973 % and 32.2 %, respectively) than the parent synthetic and natural ZSM-5.