Fe powder

Two categories of solid reductants/catalysts have been utilised in this work: (i) bulk iron and iron oxides; and (ii) supported iron catalysts. The bulk iron materials were Fe powder (≥99 %, Sigma Aldrich), Fe₂O₃ (99 % metal basis, Alfa Aesar) and Fe₃O₄ (97 % metal basis, Alfa Aesar); these were used without further treatment or modification. The supported catalysts comprised an alumina supported iron catalyst Fe/Al₂O₃ (35 % loading, Johnson Matthey Catalysts) and two zeolite‐supported catalysts (Fe/H‐ZSM‐5 and Fe/HY) synthesised in‐house. The bare zeolites (H‐ZSM‐5 extrudate, SiO₂/Al₂O₃ mole ratio=1:38, ACS material; and H‐zeolite Y powder, SiO₂/Al₂O₃ mole ratio=5.1:1, Alfa Aesar) and a commercial alumina [Puralox SBa200 (Sasol)] were also studied for comparison. The SiO₂/Al₂O₃ mole ratios for the zeolites were supplied by the manufacturers. In the case of the extrudates this ratio refers to the zeolite component; ZSM‐5 was in the H‐form in the supplied extrudates.

In a typical synthesis process, excess amount of Fe powder (2.0 g, Sigma‐Aldrich, 99%) was reacted with 10 mL of H₂SiF₆ aqueous solution (25wt%, Sigma‐Aldrich) for 24 h. The mixture was then centrifuged to harvest the solids. The as‐received solids were then diluted to 20 mL with distilled water to get a FeSiF₆ aqueous solution. 3 g PVP powder (Sigma‐Aldrich, average Mw ≈6500) was dissolved in 20 mL ethanol (Sigma‐Aldrich, 99.8%) and stirred for 2 h. Then the as‐prepared FeSiF₆ and PVP alcohol solution was mixed and stirred for 2 h to obtain precipitates. Afterward, the precipitates were dried in oven under vacuum at 60°C overnight. To completely remove the solvent, the obtained powder was grinded and further dried at 150°C in vacuum. Finally, the powder was annealed at 260°C for 4 h followed by annealing at 550°C for 3 h under an argon flow. To obtain nano‐FeF₂ powder without PDC, the FeSiF₆ aqueous solution was dried and annealed at 260°C for 4 h under an argon flow, in which the following chemical reaction takes place: FeSiF₆ → FeF₂ + SiF₄ (gas).