Speaker
Description
Iron-based catalysts are considered active for the hydrogenation of CO2 towards high-order hydrocarbons.$^{1-3}$ Here, we address the structural and chemical evolution of oxide-supported iron nanoparticles (NPs) during the activation stages and during the CO2 hydrogenation reaction. Fe NPs were deposited onto planar SiO$_{2}$ and Al$_{2}$O$_{3}$ substrates by dip coating with a colloidal NP precursor and by physical vapor deposition of Fe.$^{4}$ The model catalysts were studied in situ by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) sequentially in pure O$_{2}$, in H$_{2}$, and in the CO$_{2}$ + H$_{2}$ (1:3) reaction mixture in the mbar pressure range. The NAP-XPS results revealed the preferential formation of Fe(III) and Fe(II) surface oxides under reaction conditions, independently of the initial degree of iron reduction prior to the reaction, suggesting that CO$_{2}$ behaves as an oxidizing agent even in excess of hydrogen. The formation of the iron carbide phase, often invoked for the Fe-based catalysts in this reaction, was never observed in our model systems, even on the samples exposed to high pressure and temperature (10 bar of CO$_{2}$ + H$_{2}$, at 300°C). However, the iron carbide was observed on large (> 20 nm) NPs deposited on nanocrystalline silica and alumina supports as well as on the unsupported catalysts, monitored in situ by X-ray absorption spectroscopy (XAS). Our findings are assigned to size-dependent interaction of the Fe-oxide NPs with the support that affects the reduction in hydrogen and the carburization during CO$_{2}$-FTS. The results highlight the important role played by the oxide support in the final structure and composition of nano-sized catalysts.
References
1. M.D. Porosoff, et al., Energy & Environmental Sci 9, 62(2016).
2. W. Li, et al., RSC Advances, 8, 7651(2018).
3. Y. H. Choi, et al., Appl Catal B, 202, 605(2017).
4. M. Lopez Luna, et al., ACS Catalysis 11, 6175(2021).
| Abstract Number (department-wise) | ISC 19 |
|---|---|
| Department | ISC (Roldán) |
