Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions

Vanadium-based catalysts play a pivotal role in the emission control of industrial NO_x 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 NO_x 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 ∼ 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⁺ → 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 NO_x concentrations, especially in complex flue gases.