Synthesis and Characterization of Fe-Substituted ZSM-5 Zeolite and Its Catalytic Performance for Alkylation of Benzene with Dilute Ethylene

Abstract

A series of Fe-substituted ZSM-5 zeolite samples with an almost constant Si/(Fe + Al) molar ratio of 50 but varied levels of Fe substitution were synthesized via an in situ seed-induced hydrothermal method in a fluoride medium. Additionally, a hierarchical Fe-substituted sample with high diffusion capability was also produced by a subsequent alkaline treatment. The textural and acidic properties of these samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV−Raman, Fourier transform infrared (FT-IR), UV−vis, H 2 -temperature programmed reduction (TPR), Ar adsorption−desorption, NH 3 -temperature-programmed desorption (TPD), X-ray fluorescence (XRF), 27 Al, and 29 Si magicangle spinning (MAS) NMR analysis. These analyses revealed that Fe 3+ species were effectively integrated into the MFI framework of the Fe-substituted samples. The as-synthesized samples displayed orthogonally intergrown crystal plates of increased aspect ratios with increased Fe-substitutions. More significantly, the resulted Fe-substituted samples displayed a noticeably reduced acid strength compared to the pure ZSM-5. Evaluated by the benzene alkylation reaction with dilute ethylene, the 50% partially Fe-substituted ZSM-5 sample showed a combined high ethyl selectivity and long catalytic lifetime among all catalysts studied, which is attributed to its suitably balanced acid strength.

Fe-Substituted Pt/HZSM-48 for Superior Selectivity of i-C12 in n-Dodecane Hydroisomerization

“…The strength of strong acid sites seems to reduce slightly from Fe-free HZ48 to Fe-substituted HZ48- x , as seen by the progressive shift to lower desorption peak temperatures. This is expected, as the acid strength of Si–OH–Al is known to be higher than that of Si–OH–Fe hydroxyl groups in the zeolite framework …”

“…This is expected, as the acid strength of Si− OH−Al is known to be higher than that of Si−OH−Fe hydroxyl groups in the zeolite framework. 36 Estimated from the total area of the two deconvoluted desorption peaks, the total acidity of each sample is calculated and provided in Table 3. 37 As seen in the table, the total acidity increases noticeably from the Fe-free HZ48 to low Fesubstituted HZ48-9 but then decreases progressively with further increased Fe-substitution.…”

Understanding the Role of Fe Doping in Tuning the Size and Dispersion of GaN Nanocrystallites for CO2-Assisted Oxidative Dehydrogenation of Propane

“…In addition, the counterpart of Fe 2 O 3 /silicalite-1 showed a very broad absorption band at the range of 350−500 nm owing to the presence of oligomeric FeO x species. 49,50 By comparison, both 2000-Fe-silicalite-1 and 1000-Fe-silicalite-1 exhibited only one absorption band at 243 nm, whereas 500-Fe-silicalite-1 and 100-Fe-silicalite-1 also showed a weak band at 374 nm and a broad band at above 400 nm in addition to that band at 243 nm. Together with XRD and TPR results, it can be further confirmed that, in the cases of 2000-Fe-silicalite-1 and 1000-Fe-silicalite-1, Fe atoms were dominantly doped within the framework of silica tetrahedron via isomorphous substitution.…”

Effect of H2SiF6 modification of IM-5 on catalytic performance in benzene alkylation with ethylene

“…This is associated with the oxidation of “harder” coke deposited on the catalyst during the alkylation reaction. 43 Moreover, the second weight loss event arises at a significantly lower and broader temperature range of 200–500 °C when the reaction temperature decreased. Such low and broad decomposition temperatures is likely due to the desorption or oxidation of “softer” coke (polymerization of ethylene).…”