(417a) Selective Removal of SOx, NOx, and H2S Using NiO/SBA-15 in a Chemical Looping-Based Pollutant Removal Scheme.

Greenhouse gas emissions from flue gas generated during fossil fuel combustion remain a critical contributor to global climate change. While carbon capture technologies are actively being developed to address this issue, flue gas streams from industrial processes also contain trace levels of toxic impurities such as nitrogen oxides (NO_x), sulfur oxides (SO_x), and hydrogen sulfide (H₂S). The presence of these pollutants poses a significant challenge to achieving complete carbon capture, as their removal is necessary to prevent corrosion, catalyst poisoning, and downstream processing inefficiencies. Conventional treatment methods rely on multiple systems—flue gas desulfurization (FGD) for SO_x, the Claus process for H₂S, and selective catalytic reduction (SCR) for NO_x—each of which adds cost, energy demand, and complexity due to the need for separate units and infrastructure. To address these limitations, we propose a novel chemical looping approach for the selective removal of NO_x, SO_x, and H₂S using a single-reactor system. The proposed system employs nickel oxide (NiO) as the oxygen carrier due to its high reactivity and inertness towards CO₂. Upon reduction to metallic Ni, the material undergoes cyclic redox reactions, selectively interacting with the target pollutants while maintaining a pure CO₂ stream suitable for downstream capture. To improve dispersion and stability, NiO was supported on mesoporous SBA-15 using a wet impregnation method, resulting in the formation of NiO/SBA-15. This support was selected over others based on its superior performance, attributed to its highly ordered pore structure, which promoted uniform NiO distribution, faster reaction kinetics, and improved cyclic redox stability. The optimized NiO/SBA-15 material was then subjected to a three-step chemical looping process: (1) reduction of NiO/SBA-15 in hydrogen to form Ni/SBA-15; (2) reaction of the reduced material with NO, SO₂, and H₂S, forming corresponding oxides and sulfides of nickel; and (3) regeneration in air to restore the NiO phase. Thermogravimetric analysis (TGA) revealed that NiO/SBA-15 exhibited a ~140% increase in H₂S uptake compared to NiO/SiO₂, with stable performance sustained over 10 redox cycles. Uptake improvements for SO₂ and NO were similarly significant, with increases of ~67% and ~316%, respectively, highlighting the material's enhanced ability to react with the pollutant and cyclic stability. To further validate the phase integrity of the material, X-ray diffraction (XRD) analysis was performed, confirming the complete regeneration of the NiO phase after 10 cycles. Fixed-bed reactor studies aim to assess the oxygen carrier’s reactivity and pollutant capture efficiency under conditions that closely simulate practical applications. Additional characterizations—including BET analysis, pore size distribution, and scanning and transmission electron microscopy (SEM and TEM)—are employed to understand the influence of morphology on reactivity. This study establishes NiO/SBA-15 as a promising oxygen carrier for the integrated removal of SO_x, NO_x, and H₂S, demonstrating enhanced redox stability, high pollutant uptake, and compatibility with CO₂ capture processes.