Iron oxide-supported InNi₃C_0.5 intermetallic catalyst for the CO₂ hydrogenation to methanol: Effect of pyrolyzed Fe₂O₃ support precursors

Interest in renewable methanol produced from green hydrogen and CO₂ has given particular momentum to the exploration of efficient catalysts. Although the newly developed InNi₃C_0.5/Fe₃O₄ catalyst, derived from the In₂O₃-NiO/α-Fe₂O₃ system, shows significant potential as a catalyst for the CO₂ hydrogenation to methanol reaction, a comprehensive understanding of the chemical and structural origins that are inherently linked to catalyst synthesis is still insufficient. Herein, the study is focused on the effect of α-Fe₂O₃ precursors on catalyst performance of as-obtained InNi₃C_0.5/Fe₃O₄. A series of α-Fe₂O₃ oxides obtained by directly pyrolyzing 6 routine ferric/ferrous organic acid salts, were used as support precursors for InNi₃C_0.5/Fe₃O₄ catalyst preparation by the impregnation/carburation method. With no exception, the InNi₃C_0.5/Fe₃O₄ could be well formed in all cases while showing strong dependence of catalytic performance on their support source. The catalyst obtained by using the α-Fe₂O₃ pyrolyzed from (NH₄)₃Fe(C₂O₄)₃·3H₂O came out on top, achieving 12.6% CO₂ conversion and 90.5% methanol selectivity for a feed gas of H₂/CO₂ = 5/1, at 260 °C, 4.0 MPa and 12,000 mL g_cat⁻¹ h⁻¹. The others showed either low activity or poor selectivity (especially with CH₄ formation). Additional research reveals that the oxygen deficiency in the catalysts prepared through direct pyrolysis of organic acid salts exhibits variations. Concurrently, experimental data indicates a positive correlation between the oxygen deficiency and the strength of the electronic metal-support interaction (EMSI) in these catalysts. Moreover, this approach would be a cleaner way to obtain a qualified InNi₃C_0.5/Fe₃O₄ catalyst, compared to the precipitation method previously used for α-Fe₂O₃ preparation from iron nitrates with discharge of a large amount of high concentration nitrogen-containing wastewater.