One-step post-synthesis treatment for preparing hydrothermally stable hierarchically porous ZSM-5

From waste to catalyst: Growth mechanisms of ZSM-5 zeolite from coal fly ash & rice husk ash and its performance as catalyst for tetracycline degradation in fenton-like oxidation

Coal fly ash (CFA), an industrial solid waste, can be utilized to synthesize Zeolite Socony Mobil-5 (ZSM-5) by incorporating an external silica source. In this study, a series of ZSM-5 zeolites were synthesized using rice husk ash (RHA) as the primary silica source and CFA as the primary aluminum source under controlled hydrothermal reaction conditions, and the growth mechanism of ZSM-5 was investigated. The process of ZSM-5 growth was featured by the transformation of hyperpoly silico-aluminate in CFA and RHA into monomers. These monomers formed crystal nuclei connected in a five-membered ring structure under the influence of Tetrapropyl ammonium hydroxide (TPAOH). The surplus monomeric silica-aluminate grew on the nucleus surface due to the addition of the silica source within RHA (RHA-SiO2), ultimately resulting in the development of ZSM-5 zeolite. Characterization results demonstrated that RHA-SiO2 exhibited favorable physical and chemical properties during the ZSM-5 synthesis, with a crystallinity of 99.03%, a specific surface area of 321.19 m2/g, a weight loss of only 3.06% at 800 °C and a total acidity of 0.65 mmol/g. To evaluate the catalytic performance of ZSM-5, Fe/Cu-modified ZSM-5 was developed and used as the catalyst for the degradation of tetracycline (TC) in Fenton-like oxidation. The results indicated that Fe/Cu-ZSM-5 exhibited excellent activity and stability as the catalyst for TC degradation and mineralization. The maximum TC degradation rate reached 99.02% in 10 min and the TOC removal could be up to 69.32% in 2 h. Characterization results indicated that the Fe/Cu ions redox cycle accelerated the generation of active species (1O2 and ˙OH) in Fenton-like systems. The ZSM-5 zeolite synthesized from solid waste demonstrated superb stability and catalytic activity, leading to the effective removal of TC. Since real wastewater generally contains various pollutants, future research efforts should focused on multi-pollutant treatment.

Optimization of hierarchical ZSM-5 structure from kaolin as catalysts for biofuel production

Optimization of hierarchical ZSM-5 structure by variation of the first hydrothermal step at different times provides insight into the evolution of micro/mesopores and its effect as a catalyst for deoxygenation reaction. The degree of tetrapropylammonium hydroxide (TPAOH) incorporation as an MFI structure directing agent and N-cetyl-N,N,N-trimethylammonium bromide (CTAB) as a mesoporogen was monitored to understand the effect towards pore formation. Amorphous aluminosilicate without the framework-bound TPAOH achieved within 1.5 h of hydrothermal treatment provides flexibility to incorporate CTAB for forming well-defined mesoporous structures. Further incorporation of TPAOH within the restrained ZSM-5 framework reduces the flexibility of aluminosilicate gel to interact with CTAB to form mesopores. The optimized hierarchical ZSM-5 was obtained by allowing hydrothermal condensation at 3 h, in which the synergy between the readily formed ZSM-5 crystallites and the amorphous aluminosilicate generates the proximity between micropores and mesopores. A high acidity and micro/mesoporous synergy obtained after 3 h exhibit 71.6% diesel hydrocarbon selectivity because of the improved diffusion of reactant within the hierarchical structures.

One-pot Synthesis of Phosphorus-modified ZSM-5 Zeolite by Solid-state Method and its MTO Catalytic Performance

The traditional hydrothermal synthesis strategy of ZSM-5 zeolite is energy-consumption accompanying by pollution issues. Herein, phosphorus-modified layered ZSM-5 zeolites (PZ) were obtained by one-pot synthesis under solvent-free conditions. The synthesized samples were fully characterized by XRD, SEM, BET, NH₃ -TPD and FTIR. The effect of phosphorus addition on the morphology and catalytic activity of ZSM-5 was investigated. The results showed that phosphorus-modified ZSM-5 zeolites exhibited higher light olefin (ethylene and propylene) selectivity (above 50 %) and longer catalytic lifetime (33 h) in methanol to olefin (MTO) reaction when the weight hourly space velocity was 4 h^-1 . Phosphorus-modified ZSM-5 zeolite synthesized by in situ solvent-free method, which not only reduced the discharge of sewage but also showed a simple method to realize the introduction of phosphorous species, which provided a new idea for phosphorus modification of ZSM-5 zeolite.

Constructing single-crystalline hierarchical plate-like ZSM-5 zeolites with short b-axis length in the synthesis for catalyzing MTO reaction

ZSM-5 zeolite with hierarchical and lamellar structure is highly desired in industrial application. This paper reports an efficient additive, tetramethylguanidine (TMG), modifying crystal growth of the zeolite to this morphology....