PORE ENGINEERING AND SURFACE FUNCTIONALIZATION OF POROUS CARBON STRUCTURES DERIVED FROM BIOCHAR, AND ZEOLITES DERIVED FROM FLY ASHES

Date

2025-8-1

Author

Akın, Süleyman Şener

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This study explores two sustainable material engineering routes via nitrogen-functionalized biochars from sugar beet pulp (SBP) and iron-based zeolite catalysts derived from Turkish fly ash. In the first route, SBP was treated with 0.5 M KOH or NaOH, with or without melamine (M) or ammonium chloride (ACL) as nitrogen dopants, followed by pyrolysis at 700 °C under CO₂. KOH-treated biochars achieved higher surface areas (up to 1487 m²/g) than NaOH-treated ones. XPS analysis revealed that KOH promoted C=O groups, while NaOH favored C–OH functionalities. Nitrogen dopants introduced pyrrolic and pyridinic sites, improving graphitization (ID/IG as low as 0.66). TGA showed that alkali agents enhanced char yields via dehydration, while melamine facilitated volatile cracking and mesopore development. These effects collectively enabled the formation of high-surface-area, N-functionalized biochars with tailored microstructures. Second part of the thesis presents an integrated waste-to-catalyst strategy that transforms Class F(Seyitömer,Çatalağzı) and Class C (Soma,Yatağan) fly ash sources into Fe-loaded FAU and CHA zeolites for methane-to-methanol conversion. Fe(II) oxalate dihydrate with 98% purity was obtained using a binary sulfuric acid and oxalic acid leaching system, providing a sustainable iron source from all fly ash sources. Hydrothermal synthesis was strongly dependent on the source. Class F ash sources required lower alkalinity due to inherent Fe suppressing GIS formation and produced highly crystalline and microporous frameworks. Class C ash sources required higher alkalinity and stricter control and resulted in lower crystallinity but greater porosity. Post-synthesis treatments including aging, NH4 exchange, tailored Fe loading and steaming optimized Fe speciation, stabilized active sites and moderated acidity. Excessive steaming along with enrichment of Fe led to framework degradation. Catalytic testing at 300 °C demonstrated framework-specific behavior. FAU-type zeolites enriched in isolated extraframework Fe sites achieved high initial methanol yields but deactivated rapidly. Samples containing a significant fraction of octahedral Fe species provided more stable and sustained performance. Residual Ca and controlled extra-framework Al by softer steaming conditions improved selectivity and reduced coke formation. Class C-derived Fe-FAU samples outperformed both Class F and pure-chemical FAU analogues, achieving peak productivities of 137 μmol g⁻¹ h⁻¹ with 56 % selectivity to methanol at 20 min. CHA-type zeolites showed the strongest potential. Fe-CHA prepared from Çatalağzı Class F fly ash exhibited exceptional stability and productivity reaching 315 μmol g⁻¹ s⁻¹ with 46.1% coke-free selectivity. Çatalağzı derived Fe-CHA exceeded in methanol yield compared to Yatağan derived CHA by a factor of two to three. These results demonstrate that balancing isolated and octahedral Fe species with moderated Brønsted acidity enables the scalable, template-free synthesis of Fe-zeolite catalysts from fly ash with competitive performance for methane-to-methanol conversion. This work highlights the potential of industrial and agricultural residue valorization as a platform for producing high-performance catalytic materials for sustainable chemical processes.

Subject Keywords

fly ash, Selective Fe Recovery, Biochar, Zeolite Catalyst, Methane to Methanol

URI

https://hdl.handle.net/11511/115606

Collections

Graduate School of Natural and Applied Sciences, Thesis