(236b) Inherent Dual-Functional Ca-Fe Materials Derived from Steel Slag for Integrated CO2 Capture and Utilization

Lime (CaO), derived from the calcination of natural limestone (CaCO₃), is a fundamental raw material widely employed across various natural and industrial processes. Calcium-based materials can also serve as dual-functional materials (DFMs) in integrated CO₂ capture and utilization (ICCU) systems, simultaneously capturing CO₂ from flue gases and converting it into high-value chemicals. The ICCU process typically consists of two stages: first, capturing CO₂ from gas streams such as flue gas; and second, switching to a reducing atmosphere (e.g., H₂ or CH₄) to convert the adsorbed CO₂ in situ. Compared to conventional carbon capture and storage (CCS) and carbon capture and utilization (CCU), the ICCU approach offers substantial advantages by minimizing the external energy required for CO₂ compression, transportation, and purification. Moreover, leveraging renewable resources such as green or blue hydrogen further enhances ICCU's environmental and economic viability. Among various ICCU pathways, the integration of CO₂ capture with the reverse water–gas shift (RWGS) reaction for syngas production (ICCU-RWGS) is considered one of the most promising.

In contrast to traditional DFMs that rely on the addition of external catalytic materials, this study proposes DFMs derived from industrial steel slag, which inherently contains CaO as the CO₂ sorbent and Fe as the catalytic component for the ICCU-RWGS reaction. The surface and bulk properties of these DFMs were thoroughly characterized using XRD, XPS, SEM-EDS, and TEM-EDS. The results showed that raw steel slag consists predominantly of inert phases such as Ca₂Fe₂O₅ and Ca₂SiO₄, and features a dense, non-porous microstructure that restricts CO₂ adsorption and in-situ conversion. However, after acetic acid pretreatment, the modified slag exhibited the formation of smaller pores and textural development, with active Ca present in the form of CaO. This transformation led to a remarkable 28-fold improvement in CO₂ capture capacity, with the material retaining approximately 0.09 g_CO2 g⁻¹ after 10 cycles and experiencing only a 20% capacity decline.

ICCU-RWGS tests conducted in a fixed-bed reactor demonstrated that the optimized steel slag-derived DFM achieved a CO₂ uptake of 9.15 mmol g⁻¹, 87% CO₂ conversion, a CO yield of 7.80 mmol g⁻¹, and 100% CO selectivity at 650 °C—far exceeding the performance of untreated steel slag (CO₂ capacity < 1.0 mmol g⁻¹, CO yield = 0.73 mmol g⁻¹). In-situ XRD and FTIR analyses confirmed the presence of both self-sustaining CO₂ sorption (CaO) and catalytic (Fe) functionalities, which are highly effective for the conversion of low-calorific-value waste gases. Overall, this work demonstrates the viability of converting steel industry waste into high-performance DFMs and presents a compelling pathway for sustainable carbon management through ICCU.