Jiaying Xing,Qitong Xue,Jianjun Chen,Jinxing Mi,Xiaoping Chen,Jianqiang Shi,Zhiming Liu,Junhua Li
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 ∼ 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 NOx concentrations, especially in complex flue gases.
Due to their low activation energy and high mobility of proton transfer, protonic ceramic cells (PCCs), including protonic ceramic fuel cells (PCFCs) and protonic ceramic electrolysis cells (PCECs), working at relatively low temperatures (400–700 °C) have gained increasing attention as promising and highly efficient energy conversion and storage technologies to replace the oxide ion-conducting, high-temperature solid oxide cells (SOCs). However, similar to SOCs, Fe–Cr based alloys are also commonly used as metallic interconnects in PCCs. Thus, the practical applicability of Ba-containing proton conducting electrolytes in PCCs is fundamentally related to their tolerance and resistance towards the deposition and poisoning of the volatile chromium species from the Fe–Cr based interconnect. This study focuses on the interaction between the Cr species and the most widely used proton conducting electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) within a temperature range from 400 °C to 700 °C. Results indicated that barium oxide and the BZCYYb1711 powder reacted with the Cr2O3 powder at 250 °C and 400 °C, respectively, while the deposition of Cr species on the BZCYYb1711 electrolyte surface occurred at temperatures as low as 500 °C. Ba segregated from the BZCYYb1711 electrolyte and reacted with gaseous Cr species, forming BaCrO4 and causing a significant depreciation in Ba content in the electrolyte. The Cr species also diffused into the inner layer of BZCYYb1711, leading to the segregation of CeO2 and degrading the conductivity of the electrolyte. This study demonstrates that the deposition and poisoning of the Cr species from the Fe–Cr based metallic interconnect are serious issues for the practical and long-term applicability of Ba-containing protonic ceramic materials in PCCs.
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