RESUMEN
Tandem catalysis is widely adopted for multipollutant control in mobile sources but has rarely been reported in stationary source emission elimination. This work proposed a tandem arrangement way with up-streamed V2O5/TiO2 + down-streamed Cr2O3/TiO2 catalysts, which could achieve the efficient synergistic control of NOx and C3H8 in industrial flue gas. Moreover, this arrangement successfully alleviated the unwanted N2O formation during the NH3 -SCR process. Compared to the conventional impregnation method of the Cr2O3-V2O5/TiO2 catalyst, the tandem catalysts of V2O5/TiO2 + Cr2O3/TiO2 could enhance the NOx and C3H8 conversion by 4.2% and 39.5%, respectively, at 350 °C. It might be attributed to the fact that Cr species was the active site for C3H8 oxidation, and the tandem arrangement of catalysts was beneficial to even dispersion of active components on supports. Furthermore, due to the preferential NOx removal over the up-streamed V2O5/TiO2 catalyst, the tandem catalysts obviously alleviated the N2O formation caused by Cr species during the NH3-SCR process. Herein, it significantly decreased N2O formation by 240.5% at 350 °C compared to the Cr2O3-V2O5/TiO2 catalyst, achieving multipollutant emission control from industrial flue gas with the performance of "one stone three birds".
RESUMEN
Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 â¼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ â V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.