# Synthesis and Characterization of Iron-Based Catalysts for Carbon Dioxide Valorization
## 2 Materials and Methods  
Magnetite nanoparticles (Fe\({}_{3}\)O\({}_{4}\)) were synthesized through the co-precipitation method, using ammonia (NH\({}_{3}\)) as the precipitating agent. Iron precursors, 2.58 g FeCl\({}_{2}\)-4H\({}_{2}\)O and 7.03 g FeCl\({}_{3}\)-6H\({}_{2}\)O (molar ratio = 1:2), were dissolved in 100 mL of deionized water under nitrogen gas flow, remaining under mechanical stirring at room temperature. Then, 15 mL of 25% NH\({}_{3}\) (\(w\)/\(w\)) were added to the solution, and subsequently a black precipitate was observed. The suspension was kept under stirring for 30 min. Sonication (15 min) to break through any aggregates was performed to the resulting suspension, employing a Branson 3510 ultrasonic cleaner. For the sonicator bath, deionized water was used. Finally, the suspension was washed with deionized water to remove the chloride ions until pH = 7 was obtained. The addition of alkalis such as Na and K to magnetite nanoparticles with a molar ratio (Fe:Na or K) 1:1 (A) and 1:2 (B) was performed by adding NaCl (0.97 g for A and 0.48 g for B) and KCl (0.76 g for A and 0.38 g for B) to the precursors' mixture. Then, the procedure mentioned above was followed. The addition of Zn was successful using the following precursors: 1.29 g FeCl\({}_{2}\)-4H\({}_{2}\)O, 7.03 g FeCl\({}_{3}\cdot\)6H\({}_{2}\)O, and 1.93 g Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O (molar ratio = 0.5:0.5:2). All the synthesized nanoparticles were dispersed on HZSM-5 zeolite (SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) = 80), which was commercially available (Zeolyst International, Conshohocken, PA, USA). The zeolite was initially calcined at 500 \({}^{\circ}\)C, under air flow, for 4 h, and 1 g of it was mixed with 2 mL of Fe\({}_{3}\)O\({}_{4}\) suspension, resulting in 5 wt%. oxide loading. The mixture was left to dry in air (120 \({}^{\circ}\)C) for almost an hour, in a Venticell drying oven. The same procedure was followed for all synthesized nanoparticles. Table 1 summarizes all synthesized materials, both supported and unsupported. BET surface areas, pore volumes, and average pore diameters were determined by N\({}_{2}\) physisorption at \(-\)196 \({}^{\circ}\)C, using an Autosorb-1 Quantachrome flow apparatus. Prior to measurements, samples were dried under vacuum overnight at 250 \({}^{\circ}\)C. The total pore volume was defined as the single point pore volume at a relative pressure of _p_/_p_\({}_{o}\) = 0.95. XRD patterns of the catalyst were obtained using a Bruker D8 ADVANCE diffractometer (Bruker Corporation, Billerica, MA, USA) with Cu Ka radiation (\(\lambda\) = 1.54 A) at a scan rate of 0.02\({}^{\circ}\)/sec (26), from 5.0-80.0\({}^{\circ}\). FT-IR measurements were performed with FT-IR 6700 spectrometer (JASCO International Co. Ltd., Tokyo, Japan). All the samples were dried before the measurement as humidity affects the resulting spectra. Raman spectra were recorded in the 100-3200 cm\({}^{-1}\) region using a micro-Raman (Renishaw Qontor in-Via) Spectrometer (Renishaw plc, Gloucestershire, UK), equipped with a 532 nm (delivering \(\sim\)7.5 mW) laser that was used as an excitation source. The particle size distribution (PSD) of the produced iron nanoparticles was determined by Dynamic Light Scattering (DLS, Cordouan Technologies SAS, Pessac, France), while that of HZSM-5 was determined by a laser ensemble diffraction method (Malvern Mastersizer, Worcestershire, UK). SEM images were obtained employing a JEOL JSM-IT500 Microscope (JEOL, Peabody, MA, USA), equipped with an OXFORD INCA x-act EDS (Oxford Instruments, Oxfordshire, UK), in the Secondary Electron mode at an accelerating voltage of 20 kV under high vacuum. The nanoparticles were also characterized for their morphology by transmission electron microscopy (TEM, JEOL JEM-2011) (JEOL, Peabody, MA, USA), dispersed on a holey carbon grid, and analyzed at 200 keV. NH\({}_{3}\)-TPD measurements were conducted in a non-commercial custom-built gas flow system, using a quartz reactor.