Potential Risk of Significant N 2 O Emission without Changing NO x Conversion on Commercial V 2 O 5 /TiO 2 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 N 2 O under complex working conditions. This work reports that a commercial V 2 O 5 /TiO 2 catalyst may lead to significant N 2 O emission without greatly changing the outlet NO x concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N 2 O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N 2 O/(N 2 O+N 2 ) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N 2 O 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 V 2 O 5 /TiO 2 surface accelerates the conversion of V 4+ + Cr 6+ → V 5+ + Cr 3+ , leading to a larger proportion of surface V 5+ . More importantly, surface V 5+ is highly related to the redox property of the V 2 O 5 /TiO 2 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 NH 3 -SCR process, monitoring N 2 O emission should be included along with the NO x concentrations, especially in complex flue gases.