Research on the effect of selective adsorption of CO2 by C@Fe3O4 for H2 purification

Abstract

In the context of global efforts to address climate change, capturing and storing CO₂, as well as developing hydrogen energy, have emerged as widely recognized effective methods for reducing greenhouse gas emissions. In particular, the process of hydrogen production through the gasification and reforming of organic fuels necessitates the separation and purification of H₂ from CO₂. Although various technological pathways have been proposed in this research field, issues such as low separation efficiency, high energy consumption, and high costs are prevalent to varying degrees across these different methods. This study is based on reports of the strong interaction between ferric oxide (Fe₃O₄) and CO₂, as well as the magnetic exclusion of hydrogen gas. This study hypothesize carbon-coated magnetite (C@Fe₃O₄) as a material with selective adsorption of CO₂, enabling efficient separation of H₂ and CO₂. To test this hypothesis, this study synthesized C@Fe₃O₄ and conducted isothermal adsorption tests to determine the adsorption curves for H₂ and CO₂, along with calculations for adsorption selectivity. The results indicated that C@Fe₃O₄ exhibited good selectivity for CO₂ over H₂ under ambient conditions. Penetration experiments further confirmed that the separation ratio for H₂ and CO₂ reached as high as 13.6. Comparative experiments with porous carbon materials lacking the Fe₃O₄ core, along with characterization analyses of C@Fe₃O₄, validated the dual mechanism at play: the strong adsorption of CO₂ by the Fe₃O₄ core and the magnetic exclusion of hydrogen. The carbon coating did not inhibit the strong adsorption of CO₂ by Fe₃O₄ but also provided a barrier that prevented direct contact between H₂ and Fe₃O₄, mitigating any potential reduction reactions that could lead to magnetic decay. Moreover, the petal-like carbon-coated structure increased the volumetric CO₂ adsorption capacity of the material. Although the high density of the Fe₃O₄ crystalline core resulted in modest mass adsorption capacity, the unique layered carbon structure enhanced the specific surface area. This dual effect led to a volumetric CO₂ adsorption capacity of 1.32 mmol/cm³, surpassing that of most existing porous carbon materials, and the CO₂/H₂ adsorption ratio also exceeded that of many carbon materials.