Search

The performance of a commercial NH3-SCR catalyst used for 20,000 h in a 660 MW coal fired power plant was evaluated after treated in situ with water vapor at 300–350 °C for 336 h. The conversion of NOx reached 91.4% after this water treatment. The recovery of catalytic activity is mainly due to the removal of potassium, arsenic and sulfate-containing deposits from the catalyst surface, as well as the increase of surface active oxygen species and specific surface area. These results indicate that commercial NH3-SCR catalysts are deactivated by the deposition of water-soluble substances and which can be in situ regenerated cost-effectively with high-temperature water vapor treatment.

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-NOx 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.