In situ treatment by high-temperature water vapor as a novel health-care approach for commercial SCR catalyst

Highlights: • High-temperature water vapor could extend the lifetime of SCR catalyst. • High-temperature water vapor could remove poisonous depositions on SCR catalyst. • Textual, acid and surface properties of SCR catalyst could be enhanced by water vapor. • V⁵⁺ could be reduced to V⁴⁺ during H₂O adsorption and dissociation on SCR catalyst. Commercial selective catalytic reduction (SCR) catalysts used in a 1000 MW coal-fired power plant were in situ treated by high-temperature water vapor. The de-NO_x efficiency of the deactivated catalyst increased about 25–30%, comparable to fresh commercial SCR catalysts, after being treated with simulated flue gas with 15–20 vol% high-temperature water vapor. It indicates that treatment by in situ 15–20 vol% high-temperature water vapor could significantly extend the lifetime of commercial SCR catalyst. High-temperature water vapor could remove Fe, Na, Ca, sulphate species and SiO₂ depositing on SCR catalyst. Compared with the deactivated catalyst, the specific surface area, the ratio of V⁴⁺/V⁵⁺ and Lewis acid content of health-care catalyst increased from 41.679 to 44.596 m²·g⁻¹, 1.35 to 1.80 and 45.5 to 73.8%, respectively. Density functional theory (DFT) calculation demonstrated that the electrons transferred from H₂O molecule to V⁵⁺ cations in the process of H₂O adsorption and the subsequent hydroxylation of V⁵⁺cations during H₂O dissociation contribute to the reduction of V⁵⁺ to V⁴⁺ on the SCR catalyst.