Tuning the catalytic properties of La–Mn perovskite catalyst via variation of A- and B-sites: effect of Ce and Cu substitution on selective catalytic reduction of NO with NH3

Abstract

Perovskites with flexible structures and excellent redox properties have attracted considerable attention in industry, and their denitration activities can be further improved with metal substitution. In order to investigate the effect of Ce and Cu substitution on the physicochemical properties of perovskite in NH₃-SCR system, a series of La_1−xCe_xMn_1−yCu_yO₃ (x = 0, 0.1, y = 0, 0.05, 0.1, 0.2, 0.4) catalysts were prepared by citrate sol-gel method and employed for NO removal in the simulated flue gas, and the physical and chemical properties of the catalysts were studied using XRD, SEM, BET, XPS, DRIFT characterizations. The Ce substitution on A-site cation of LaMnO₃ can improve the denitration activity of the perovskite catalyst, and La_0.9Ce_0.1MnO₃ displays NO conversion of 86.7% at 350 °C. The characterization results indicate that the high denitration activity of La_0.9Ce_0.1MnO₃ is mainly attributed to the larger surface area, which contributes to the adsorption of NH₃ and NO. Besides, the appropriate Cu substitution on B-site cation of La_0.9Ce_0.1MnO₃ can further improve the denitration activity of perovskite catalyst, and La_0.9Ce_0.1Mn_0.8Cu_0.2O₃ displays the NO conversion of 91.8% at 350 °C. Although the specific surface area of La_0.9Ce_0.1Mn_0.8Cu_0.2O₃ is lower than La_0.9Ce_0.1MnO₃, the Cu active sites and the Ce³⁺ contents are more developed, making many reaction units formed on the catalyst surface and redox properties of catalyst improved. In addition, strong metal interaction (Ce⁴⁺ + Mn²⁺ + Cu²⁺ ↔ Ce³⁺ + Mn³⁺/Mn⁴⁺ + Cu⁺) and high concentrations of chemical adsorbed oxygen and lattice oxygen both strengthen the redox reaction on catalyst surface, thus contributing to the better denitration activity of La_0.9Ce_0.1Mn_0.8Cu_0.2O₃. Therefore, appropriate cerium and copper substitution will markedly improve the denitration activity of La–Mn perovskite catalyst. We also reasonably conclude a multiple reaction mechanism during NH₃-SCR denitration process basing on DRIFT results, which includes the Eley–Rideal mechanism and Langmuir–Hinshelwood mechanism.