# Synthesis and Characterization of Iron-Based Catalysts for Carbon Dioxide Valorization
## 2 Materials and Methods
The materials (0.1 g) were first reduced under H\({}_{2}\) flow (200 cm\({}^{3}\) min\({}^{-1}\)) for 4.0 h at 350 \({}^{\circ}\)C and then cooled to 100 \({}^{\circ}\)C. At 100 \({}^{\circ}\)C, samples were saturated with NH\({}_{3}\) for 1 h and subsequently purged with N\({}_{2}\) for 2 h. Finally, ammonia des \begin{table}
\begin{tabular}{c c} \hline \hline
**Unsupported Materials** & **Supported Materials** \\ \hline Fe\({}_{3}\)O\({}_{4}\) & Fe\({}_{5}\)O\({}_{4}\)/HZSM-5 \\ Na-Fe\({}_{3}\)O\({}_{4}\) (A) & Na-Fe\({}_{3}\)O\({}_{4}\) (A)/HZSM-5 \\ K-Fe\({}_{3}\)O\({}_{4}\) (A) & K-Fe\({}_{3}\)O\({}_{4}\) (A)/HZSM-5 \\ Na-Fe\({}_{3}\)O\({}_{4}\) (B) & Na-Fe\({}_{3}\)O\({}_{4}\) (B)/HZSM-5 \\ K-Fe\({}_{3}\)O\({}_{4}\) (B) & K-Fe\({}_{3}\)O\({}_{4}\) (B)/HZSM-5 \\ ZnFe\({}_{2}\)O\({}_{4}\) & ZnFe\({}_{2}\)O\({}_{4}\)/HZSM-5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Synthesized materials. option was monitored by heating the sample up to 800 \({}^{\circ}\)C, at a heating rate of 10 \({}^{\circ}\)C/min, under N\({}_{2}\) flow. The concentration of ammonia was measured by a FTIR GASMETTM CR-SERIES Fourier Transform Infrared (FT-IR) (Gasmet Technologies, Vantaa, Finland) gas analyzer. CO\({}_{2}\)-TPD measurements were performed, loading 0.1 g of the sample in the same reactor employed for NH\({}_{3}\)-TPD measurements. Following a similar procedure as described above, reduced samples were saturated with CO\({}_{2}\) at 50 \({}^{\circ}\)C and purged with N\({}_{2}\) flow for 2 h. Desorption of carbon dioxide was carried out under N\({}_{2}\) flow from 50 to 700 \({}^{\circ}\)C. The concentration of carbon dioxide was measured by a HORIBA VA-5111 CO\({}_{2}\) gas analyzer (HORIBA, Kyoto, Japan). Catalytic performance tests were conducted in a stainless-steel continuous flow reactor equipped with thermocouples on top and bottom, heated line, pressure gage, condensate vessel, as well as gas inlet and outlet lines (Figure S1). Gas products of the outlet stream were analyzed online using a Shimadzu Nexis GC-2030 gas chromatographer (Shimadzu Corporation, Kyoto, Japan), equipped with a Barrier Ionization Discharge (BID) detector and a ShinCarbon ST 80/100 column (length: 30 m, diameter: 0.18 mm). Prior to the reaction, the catalytic materials were reduced at 350 \({}^{\circ}\)C for 4 h under pure H\({}_{2}\) flow, at atmospheric pressure. The typical reaction conditions were: 320 \({}^{\circ}\)C temperature, 3.0 MPa pressure, 40 mg of catalyst, and feedstock stream H\({}_{2}\)/CO\({}_{2}\) at a ratio 3:1 (total inlet flow measured with mass flow controllers: 200 mls min\({}^{-1}\)). The main gas-phase products detected under the typical experimental conditions were methane and carbon monoxide, while ethane, propylene, and propane were also detected. In all cases, water was not present in the outlet stream as any produced amount was condensed prior to the stream entering the GC for analysis. Fog presence in the condensation vessel showed that some liquid products were formed; however, their amount was not sufficient for collection and analysis. Thus, in selectivity calculations (Equation (2)), liquid products were assumed to be zero. The overall flow rate in the outlet stream of the reactor was considered equal to the inlet flow, allowing approximate approaches for all calculations, as variation of the molar flow rate is considered negligible due to low conversion levels. The carbon balance of the experiments was 97 \(\pm\) 2%.