In this work, we investigate the catalytic role of platinumdecorated defective CNC (Pt/dCNC) in CO 2 hydrogenation to formic acid (FA) by a density functional theory (DFT) approach. The reaction follows the equation CO 2(g) + H 2(g) → HCOOH (g) . Combining highly reactive Pt atoms with defective CNC provides Pt/dCNC, a reactive monodispersed atomic catalyst for CO 2 hydrogenation. We propose our new mechanism of CO 2 hydrogenation over the Pt/dCNC catalyst involving a H 2 dissociation and H spillover sequence that is energetically favorable. The rate-determining step is formic acid desorption that requires an energy barrier of 1.11 eV. Furthermore, our findings show that the rate of FA production is dependent on H 2 concentration. Altogether, the theoretical results support the concept of the spillover mechanism, playing a key role in promoting CO 2 hydrogenation via a formate intermediate. These results improve our understanding of the mechanism involving H 2 dissociation with the H spillover process and the catalytic reactions that are very important for the development of highly efficient catalysts for CO 2 conversion into FA.

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The effect of different active phases of Fe/SiO₂ catalyst on the physio-chemical properties and the catalytic performance in CO₂ hydrogenation under mild conditions (at 220 °C under an ambient pressure) was comprehensively studied in this work. The Fe/SiO₂ catalyst was prepared by an incipient wetness impregnation method. Hematite (Fe₂O₃) in the calcined Fe/SiO₂ catalyst was activated by hydrogen, carbon monoxide, and hydrogen followed by carbon monoxide, to form a metallic iron (Fe/SiO₂-h), an iron carbide (Fe/SiO₂-c), and a combination of a metallic iron and an iron carbide (Fe/SiO₂-hc), respectively. All activated catalysts were characterized by XRD, Raman spectroscopy, N₂ adsorption–desorption, H₂-TPR, CO-TPR, H₂-TPD, CO₂-TPD, CO-TPD, NH₃-TPD, and tested in a CO₂ hydrogenation reaction. The different phases of the Fe/SiO₂ catalyst are formed by different activation procedures and different reducing agents (H₂ and CO). Among three different activated catalysts, the Fe/SiO₂-c provides the highest CO₂ hydrogenation performance in terms of maximum CO₂ conversion, as well as the greatest selectivity toward long-chain hydrocarbon products, with the highest chain growth probability of 0.7. This is owing to a better CO₂ and CO adsorption ability and a greater acidity on the carbide form of the Fe/SiO₂-c surface, which are essential properties of catalysts for polymerization in FTs.