An Efficient Two-Step Method for NH3 Removal at Low Temperature Using CoOx-CuOx/TiO2 as SCO Catalyst Followed by NiMn2O4 as SCR Catalyst

A novel two-step method was designed for NH3 removal at low temperature (150–200 °C) in this work. In step 1, the selective catalytic oxidation of NH3 to NOx occurred on the SCO catalyst to make the outlet [NH3]/[NOx] ≈ 1. In step 2, the selective catalytic reduction of formed NOx by unreacted NH3 occurred on the SCR catalyst, so as to improve the NH3 removal efficiency and N2 selectivity of the whole two-step reaction process. For the step 1 catalyst, a series of TiO2 supported transition metal oxides catalysts were prepared and tested to select the suitable one. The two-step method showed superior catalytic performance with the NH3 removal efficiency higher than 95% as well as the N2 selectivity higher than 85% in 170–180 °C by using 7.5CoOx-7.5CuOx/TiO2 as the step 1 catalyst and NiMn2O4 as the step 2 catalyst. The analysis of the N2O formation indicated that the N2O formation of the two-step method mainly consisted of the N2O formed in step 1 and step 2 catalysts. The N2 selectivity of the two-step method at 150–170 °C can be improved by the following ways: reducing the N2O formed by NH3 oxidation on the step 2 catalyst, increasing the NOx formed on the step 1 catalyst to inhibit the oxidation of NH3 on the step 2 catalyst, and further reducing the N2O formation on the step 1 catalyst.