# Synthesis and Characterization of Iron-Based Catalysts for Carbon Dioxide Valorization
## 5 Conclusions  
This study employs iron-based catalysts, doped with alkalis (Na, K) and zinc, supported on zeolite for the conversion of CO\({}_{2}\) into C\({}_{2+}\) hydrocarbons. Synthesized materials have been physico-chemically characterized, and their catalytic performance has been evaluated through preliminary tests. The iron phases detected on the synthesized materials correspond primarily to magnetite (Fe\({}_{3}\)O\({}_{4}\)) and maghemite (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)). TEM results prove that alkali ions have been successfully incorporated within the Fe\({}_{3}\)O\({}_{4}\) lattice. Both SEM and TEM micrographs show that iron nanoparticles are well dispersed on the HZSM-5 surface indicating close proximity, especially for the Na-Fe\({}_{3}\)O\({}_{4}\) (A)/HZSM-5 catalyst, which presented enhanced selectivity to CH\({}_{4}\) and reduced selectivity to CO. Preliminary tests show that product distribution is highly affected by the presence of acid sites; low-medium acid sites and medium acidity values of the above samples are correlated with the formation of C\({}_{2+}\) hydrocarbons. In general, among the supported samples, Fe\({}_{3}\)O\({}_{4}\)/HZSM-5 and Na-Fe\({}_{3}\)O\({}_{4}\) (A) /HZSM-5 are the most promising for promoting CO\({}_{2}\) conversion into C\({}_{2+}\) products, as Na addition suppresses CO formation, even though it does not affect C\({}_{2+}\), selectivity. On the other hand, K addition results in the formation of stronger acid sites that favor CO formation. Testing the catalyst under higher residence times in a larger experimental setup is anticipated to surpass the constraints of the current setup, thereby facilitating the production of higher hydrocarbons tailored for future sustainable fuels. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14114959/s1](https://www.mdpi.com/article/10.3390/app14114959/s1)]([https://www.mdpi.com/article/10.3390/app14114959/s1](https://www.mdpi.com/article/10.3390/app14114959/s1)), Figure S1: Lab testing unit flow chart; Figure S2: NH\({}_{3}\)-TPD profiles of unsupported samples; Figure S3: CO2-TPD profiles of supported samples; Figure S4: CO2-TPD profiles of unsupported samples; Figure S5: HRTEM micrograph of the Na-Fe\({}_{3}\)O\({}_{4}\) (A) unsupported sample; Figure S6: TEM micrographs of unsupported samples: (**a**) Na-Fe\({}_{3}\)O\({}_{4}\) (A); (**b**) K-Fe\({}_{3}\)O\({}_{4}\) (A); (**c**) Na-Fe\({}_{3}\)O\({}_{4}\) (B); (**d**) K-Fe\({}_{3}\)O\({}_{4}\) (B); Figure S7: Selected area electron diffraction (SAED) pattern of Fe\({}_{3}\)O\({}_{4}\); Figure S8: SEM micrographs of: (**a**) unsupported Fe\({}_{3}\)O\({}_{4}\); (**b**) supported Fe\({}_{3}\)O\({}_{4}\) on HZSM-5; (**c**) HZSM-5; Figure S9: GC raw data: (**a**) experiment without catalyst; (**b**) experiment over Na-Fe\({}_{3}\)O\({}_{4}\) (A)/HZSM-5; (**c**) experiment over Fe\({}_{3}\)O\({}_{4}\) (A)/HZSM-5 (**c**) (min): 0.585 (H\({}_{2}\)), 1.393 (CO), 2.856 (CH\({}_{4}\)), 4.375 (CO\({}_{2}\)), 6.853 (C\({}_{2}\)H\({}_{6}\)), 10.099 (C\({}_{3}\)H\({}_{6}\)), 10.718 (C\({}_{3}\)H\({}_{8}\))); Table S1: Desorbed NH\({}_{3}\) (NH\({}_{3}\)-TPD); Table S2: Desorbed CO\({}_{2}\) (CO\({}_{2}\)-TPD); Table S3: Lattice constants of alkali-doped nanoparticles. Data curation, A.B., V.Z. ([PERSON]) and G.K. ([PERSON]); Investigation, A.B., V.Z. ([PERSON]) and G.K. ([PERSON]); Methodology, A.B., [PERSON] ([PERSON]) and [PERSON] ([PERSON]); Supervision, [PERSON] ([PERSON]), [PERSON] ([PERSON]) and [PERSON] ([PERSON]); Validation, A.B. ; Writing--original draft, [PERSON] and [PERSON]. ([PERSON]); Writing--review and editing, [PERSON] ([PERSON]), [PERSON] ([PERSON]) and [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript.