Ultrasmall Fe₃O₄ Nanoparticles on ZrO₂ as Catalysts for CO₂ Hydrogenation to Lower Olefins

Organic synthesis presents significant opportunities for converting the abundant and hazardous carbon dioxide (CO₂) in the atmosphere into a more sustainable carbon source. To reduce the carbon footprint, we explored the direct hydrogenation of CO₂ to lower (C_2-4⁼) olefins using various catalysts composed of ZrO₂-supported alkali-metal-promoted superparamagnetic iron oxide nanoparticles (SPIONs; Fe₃O₄). These catalysts are notable for their straightforward preparation; we employed a cost-effective dry-mixing method to create a range of alkali metal-doped SPIONs supported on ZrO₂. Results showed that the strong interactions between Fe₃O₄ and the ZrO₂ support enhanced CO₂ hydrogenation performance compared to other forms. Under optimal conditions – using a gas hourly space velocity (GHSV) of 4500 mL/h/g_cat. and a feed ratio of H₂:CO₂=3 : 1 – this catalyst achieved over 22 % CO₂ conversion and high selectivity for light (C_2–4⁼) olefins at 30 bar and 375 °C, with 30 wt% Fe₃O₄ loading on ZrO₂ and 2 wt% K promoter. We also investigated several variables, including alkali metal concentration, iron content, reaction conditions, and catalyst stability over 96 hours.