*3.1. Preparation of Alkali-Activated Materials and Fe Catalysts*

AAMs were synthesized using powdered blast furnace slag (BFS) obtained from the Finnish steel industry. Table 5 lists the elemental composition of the slag, as determined by ICP-OES analysis.

AAMs were prepared by mixing 40 g of BFS with 17.5, 20.0, 25.0, and 30.0 g of 50 wt % sodium hydroxide (NaOH ≥ 97%, Merck, Darmsdtadt, Germany). The formed pastes were poured into molds, followed by consolidation in plastic bags at room temperature for 168 h. For comparison, consolidation was first performed at 60 ◦C for 24 h and then for 144 h at room temperature. The prepared samples were named according to their NaOH concentration and consolidation temperature (Table 6). Before use, the materials were crushed using a jaw crusher, sieved to a particle size of 0.5–2.0 mm, and washed with de-ionized water. As the active metal, Fe was impregnated on the AAMs by ion exchange. First, 5 g of AAM and 0.5 dm<sup>3</sup> of 0.01 M (NH4)2Fe(SO4)<sup>2</sup> (99.0–101.5%, Merck, Darmsdtadt, Germany) were mixed in a sand bath and left overnight at 80 ◦C. The solids were collected by filtration, washed with deionized water, and dried overnight at 120 ◦C. Finally, the prepared Fe catalysts were subjected to calcination at 500 ◦C for 2 h, increasing the temperature from room temperature to the target temperature at a rate of 1 ◦C/min.

**Table 6.** Abbreviations of the prepared AAMs and Fe catalysts. Samples were named according to their NaOH concentrations and curing temperatures.

