Promotion effect of Co addition on the activity and SO₂ tolerance of CrCe catalysts for selective catalytic reduction of NO_x with NH₃ at middle–low temperatures

Abstract

BackgroundNitrogen oxides (NOx) can result in a series of environmental issues (haze, photochemical smog and acid rain) that endanger human health. Currently, selective catalytic reduction (SCR) of NOx with ammonia (NH3‐SCR) has been considered to be one of the most efficient techniques to eliminate NOx.ResultsNovel Co‐modified chromium/cerium (CrCe) catalysts were synthesized by the citric acid method to improve their insufficient SCR activity and sulfur dioxide (SO2) resistance for NOx removal at middle–low temperatures. Cobalt (Co) addition could significantly increase the catalytic activity of CrCe catalysts, and the 5CoCrCe catalyst exhibited the highest catalytic activity with ≤95% NOx conversion and >80% N2 selectivity within 180–280 °C. In addition, the 5CoCrCe catalyst exhibited outstanding SO2 resistance as well as reversibility, with >90% NO conversion under 600 ppm SO2 for 510 min.ConclusionIt was determined by characterizations that Co addition can increase SSA, Cr6+ concentration, electron transfer between Co and Cr by redox cycle (Cr6+ + 4Co2+ ↔ 4Co3+ + Cr2+) and the redox properties of the CrCe catalyst. The 5CoCrCe catalyst surface consists mainly of Lewis acid and its NH3‐SCR reactions follows the Eley–Rideal (E–R) mechanism. The 5CoCrCe catalyst exhibited outstanding SO2 resistance due to higher Cr3+, Ce3+ and Oα concentrations and strong redox cycles (3Ce4+ + Cr3+ ↔ 3Ce3+ + Cr6+ and Cr6+ + 3Co2+ ↔ 3Co3+ + Cr3+). Furthermore, in situ DRIFTS results revealed that SO2 could induce more adsorbed NOx and NH3 species instead of bulk sulfate, which also was responsible for good SO2 resistance. © 2023 Society of Chemical Industry.