Interaction mechanism between Se species in flue gas and V2O5-MoO3/TiO2 catalyst: An in-depth experimental and theoretical study

Abstract

The deactivation of denitrification catalysts has attracted widespread attention, whereas little is known about the poisoning effect of selenium (Se) species to date. In this study, the influence of element Se (Se0), SeO2 and CaSeO3 on the activity of V2O5-MoO3/TiO2 selective catalytic reduction (SCR) catalyst were evaluated under different temperatures. It was found that under 200 °C Se species had no significant effects on the denitrification efficiency. However, the performances of the catalysts were notably suppressed over 250 °C. The interaction mechanism between Se species and V2O5-MoO3/TiO2 catalyst was unveiled via combined comprehensive characterizations and density functional theory (DFT) calculations. The results indicated that the role of CaSeO3 was mainly physical poisoning and little interaction was observed, while Se0 and SeO2 could cause chemical deactivation because of the strong electron transfer. On the catalyst surface, Se0 could react with V2O5 and MoO3 to form Se4+ species (SeO2, VxSeyOz and MoxSeyOz). The formation of VxSeyOz reduced the acid sites on the catalyst, causing irreversible denaturation of the active component V2O5. The formed MoxSeyOz could protect the V2O5 to a certain extent and decompose at higher temperatures to restore the chemical properties of MoO3. SeO2 could be reduced to Se0 by NH3, forming a SeO2 → Se0 → SeO2 cycle beside the SCR process, which continuously hindered the removal of NOx. As the temperature gradually increased, SeO2 sublimated away from the catalyst, partially restored the catalytic activity.