Excellent SO2- and H2O-tolerant via maximizing catalytic sites over three-dimensional spherical daisy-like porous Fe2O3-WO3-Al2O3 catalysts for NH3-SCR at wide temperature

Abstract

The efficient strategy for enhancing the H₂O/SO₂ resistance is to maximize the exposure of catalytic sites that are less susceptible to sulfite/sulfate species, competitive adsorption and sulfation. Herein, the porous Fe₂O₃-WO₃-Al₂O₃ (3D-FeWAl) catalysts with 3D spherical chrysanthemum-like shape structure were prepared by a double template method to reveal the structure-composition-H₂O/SO₂ resistance relationship of 3D-FeWAl materials for the NH₃-SCR reaction with H₂O + SO₂. The water and sulfur resistance mechanism for NH₃-SCR reaction over the 3D spherical daisy-like porous 3D-FeWAl catalyst was revealed. Results demonstrated that the 3D-FeWAl₁₅ catalysts exhibited the excellent SCR activity and SO₂/H₂O-tolerant, achieving above 90 % NO conversion at 250–450 °C. Al₂O₃ was introduced to increase medium and strong acidic sites, providing more oxygen vacancies and Fe³⁺-O_v-W⁵⁺ interfacial sites. Importantly, the unique spherical chrysanthemum-like shape structure, which greatly maximized the exposure of catalytic sites, facilitated mass transfer reaction sites of reactants, and enhanced sufficiently dispersed active components, protecting the active molecules from sulfation. Besides, the rich 3D hierarchical porous system effectively promotes NH₄HSO₄ decomposition and weak SO₂ adsorption. The formation of an abundant hydroxyl (–OH) group from the water molecules (H₂O) at highly exposed catalytic sites results in the creation of a greater number of acidic sites for ammonia (NH₃) adsorption, thus maintaining the high-efficiency NH₃-SCR reaction. This study provides insight into the rational design of high-efficiency catalysts with good H₂O/SO₂ resistance.