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

Abstract Background Nitrogen oxides (NO x ) can result in a series of environmental issues (haze, photochemical smog and acid rain) that endanger human health. Currently, selective catalytic reduction (SCR) of NO x with ammonia (NH 3 ‐SCR) has been considered to be one of the most efficient techniques to eliminate NO x . Results Novel Co‐modified chromium/cerium (CrCe) catalysts were synthesized by the citric acid method to improve their insufficient SCR activity and sulfur dioxide (SO 2 ) resistance for NO x 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% NO x conversion and >80% N 2 selectivity within 180–280 °C. In addition, the 5CoCrCe catalyst exhibited outstanding SO 2 resistance as well as reversibility, with >90% NO conversion under 600 ppm SO 2 for 510 min. Conclusion It was determined by characterizations that Co addition can increase SSA, Cr 6+ concentration, electron transfer between Co and Cr by redox cycle (Cr 6+ + 4Co 2+ ↔ 4Co 3+ + Cr 2+ ) and the redox properties of the CrCe catalyst. The 5CoCrCe catalyst surface consists mainly of Lewis acid and its NH 3 ‐SCR reactions follows the Eley–Rideal (E–R) mechanism. The 5CoCrCe catalyst exhibited outstanding SO 2 resistance due to higher Cr 3+ , Ce 3+ and O α concentrations and strong redox cycles (3Ce 4+ + Cr 3+ ↔ 3Ce 3+ + Cr 6+ and Cr 6+ + 3Co 2+ ↔ 3Co 3+ + Cr 3+ ). Furthermore, in situ DRIFTS results revealed that SO 2 could induce more adsorbed NO x and NH 3 species instead of bulk sulfate, which also was responsible for good SO 2 resistance. © 2023 Society of Chemical Industry.