Two-dimensional materials have emerged as promising catalysts for flue gas desulfurization, particularly in the oxidation of sulfur dioxide (SO₂) due to their high surface area, tunable electronic properties, and exceptional reactivity. Among these, cerium oxide (CeO₂) nanosheets and molybdenum disulfide (MoS₂) stand out for their unique catalytic mechanisms, surface acid-base properties, and resistance to poisoning—critical factors in industrial scrubber systems.
CeO₂ nanosheets exhibit remarkable redox properties due to the facile Ce³⁺/Ce⁴⁺ transition, which enhances oxygen storage and release capabilities. This property is crucial for SO₂ oxidation, where lattice oxygen participates in the reaction, converting SO₂ to SO₃, which then reacts with water to form sulfuric acid for removal. The nanosheet morphology further increases the exposure of active (100) and (110) facets, which are more reactive than the bulk (111) surfaces. Studies indicate that CeO₂ nanosheets achieve SO₂ conversion rates exceeding 90% at temperatures around 300–400°C, significantly lower than conventional vanadium-based catalysts, which typically require 400–500°C. The surface acid-base properties of CeO₂ also play a role; the Lewis acid sites (Ce⁴⁺) adsorb SO₂, while the basic oxygen vacancies facilitate the activation of O₂, promoting oxidation.
MoS₂, a transition metal dichalcogenide, operates through a different mechanism. Its catalytic activity stems from sulfur edge sites, which act as active centers for SO₂ adsorption and subsequent oxidation. Unlike CeO₂, MoS₂ relies on its inherent sulfur-rich surface, which resists poisoning by flue gas contaminants such as arsenic or alkali metals. The basal planes of MoS₂ are inert, but engineered defects or edge-terminated nanostructures can drastically improve reactivity. When doped with transition metals like Co or Ni, the electronic structure of MoS₂ is modified, enhancing charge transfer and improving SO₂ oxidation efficiency. Experimental data show that doped MoS₂ catalysts achieve conversion efficiencies of 80–85% at 250–350°C, with minimal degradation over extended operation.
A critical challenge in flue gas desulfurization is catalyst poisoning, where impurities like fly ash or trace heavy metals deactivate traditional catalysts. CeO₂ nanosheets demonstrate high tolerance to arsenic poisoning due to their oxygen mobility, which prevents arsenic from permanently blocking active sites. Similarly, MoS₂’s sulfur edges are less susceptible to alkali metal deposition compared to metal oxide catalysts. This poison resistance translates to longer catalyst lifespans and reduced maintenance costs in industrial scrubbers.
Integration with existing scrubber systems is another advantage of 2D material catalysts. Their high surface area allows for compact reactor designs, reducing the footprint of desulfurization units. In wet scrubbers, CeO₂ nanosheets can be dispersed in slurries, where they catalyze SO₂ oxidation in the liquid phase, while MoS₂-based catalysts are more suited for dry or semi-dry systems due to their stability under lower humidity conditions. The compatibility of these materials with modular scrubber designs enables retrofitting of older plants without major infrastructure changes.
Energy efficiency is a key advantage over conventional methods. Traditional limestone-based scrubbing requires significant energy for grinding and slurry circulation, while vanadium catalysts demand high operating temperatures. In contrast, 2D material catalysts operate at lower temperatures, reducing thermal energy input. Computational analyses estimate that CeO₂ and MoS₂ catalysts can lower energy consumption by 20–30% compared to vanadium systems, with proportional reductions in CO₂ emissions from auxiliary processes.
Despite these benefits, challenges remain in scaling up production of high-quality 2D catalysts. Synthesis methods like chemical vapor deposition for MoS₂ or hydrothermal routes for CeO₂ nanosheets must be optimized for cost-effective large-scale manufacturing. Stability under cyclic operation and long-term exposure to flue gas components also requires further validation in pilot-scale studies.
In summary, 2D materials like CeO₂ nanosheets and MoS₂ offer a transformative approach to flue gas desulfurization. Their high activity, poison resistance, and energy-efficient operation position them as viable alternatives to conventional catalysts, with potential to enhance the sustainability of industrial emission control systems. Future research should focus on scalable synthesis and integration protocols to accelerate industrial adoption.