Low-temperature NH₃-SCR performance of a novel Chlorella@Mn composite denitrification catalyst

The synthesis process of conventional Mn-based denitrification catalysts is relatively complex and expensive. In this paper, a resource application of chlorella was proposed, and a Chlorella@Mn composite denitrification catalyst was innovatively synthesized by electrostatic interaction. The Chlorella@Mn composite denitrification catalyst prepared under the optimal conditions (0.54 g/L Mn²⁺ concentration, 20 million chlorellas/mL concentration, 450°C calcination temperature) exhibited a well-developed pore structure and large specific surface area (122 m²/g). Compared with MnOx alone, the Chlorella@Mn composite catalyst achieved superior performance, with ∼100% NH₃ selective catalytic reduction (NH₃-SCR) denitrification activity at 100-225°C. The results of NH₃ temperature-programmed desorption (NH₃-TPD) and H₂ temperature-programmed reduction (H₂-TPR) showed that the catalyst had strong acid sites and good redox properties. Zeta potential testing showed that the electronegativity of the chlorella cell surface could be used to enrich with Mn²⁺. X-ray photoelectron spectroscopy (XPS) confirmed that Chlorella@Mn had a high content of Mn³⁺ and surface chemisorbed oxygen. In-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) experimental results showed that both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms play a role in the denitrification process on the surface of the Chlorella@Mn catalyst, where the main intermediate nitrate species is monodentate nitrite. The presence of SO₂ promoted the generation and strengthening of Brønsted acid sites, but also generated more sulfate species on the surface, thereby reducing the denitrification activity of the Chlorella@Mn catalyst. The Chlorella@Mn composite catalyst had the characteristics of short preparation time, simple process and low cost, making it promising for industrial application.