Hierarchical ZSM-5 prepared by guanidinium base treatment: Understanding microstructural characteristics and impact on MTG and NH3-SCR catalytic reactions

An H-ZSM-5 zeolite sample consisting of large particles (5–15 μm) was synthesized and base treated using sodium hydroxide, guanidinium hydroxide and guanidinium carbonate to create a hierarchical pore system. In the case of sodium hydroxide as demetallation agent a high degree of mesoporosity was achieved and with guanidinium hydroxide, mesoporosity was observed after prolonged treatment. All samples were tested in the methanol-to-gasoline (MTG) reaction and iron-impregnated samples were tested for selective catalytic reduction of NO with ammonia (SCR). In the MTG reaction an improved catalyst lifetime was observed which has been correlated to the creation of mesopores. In the SCR reaction improved NO conversion was observed for all base treated samples. In accordance with spectroscopic results this has been attributed to a higher abundance of active and dispersed Fe sites in the base treated samples. All samples were characterized by a multitude of experimental techniques including physisorption measurements, electron microscopy and spectroscopic methods.

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► A novel post-synthesis treatment using inexpensive guanidinium bases was explored.
► Mesoporosity was generated during guanidinium hydroxide treatment.
► An improved performance in the MTG reaction was observed and correlated to the mesoporosity in the samples.
► In SCR mesoporous Fe-ZSM-5 performance also improved, though the effect was less influenced by better diffusion, but instead caused by an improved dispersion of active Fe species.