Selective Reduction Of NO_x By CO Over Ir/KIT-6 Catalysts

The control of nitrogen oxides（NO_x）is an urgent problem to be solved.Selective catalytic reduction of NO_x with CO（CO-SCR）is an efficient method for the removal of CO and NO_x in flue gas simultaneously,which has great application value.Ir/KIT-6 catalyst with high CO-SCR activity was prepared.Then,the activity of Ir/KIT-6 catalyst was further improved by adding alkali metal Rb.Finally,the catalysts was characterized by N₂ adsorption-desorption,XRD,XPS and In situ DRIFTS,and the relationship between the structure and the catalytic performance has been revealed.The reaction mechanism was also explored.The main research results are as follows:KIT-6 mesoporous materials were prepared by hydrothermal method.Ir/KIT-6 catalyst was successfully prepared by loading precious metal Ir on KIT-6.In the CO-SCR process,Ir/KIT-6 showed the highest activity at 225°C,with NO_x conversion and N₂ selectivity reaching more than 90%.Ir/KIT-6 has three-dimensional cubic symmetry（ia3d）structure with ordered mesopores,large specific surface area,stable pore volume and uniform average pore size.In situ DRIFTS showed that CO and NO were adsorbed on Ir at the same time during the reaction,and part of the linearly adsorbed NO was converted into NO₂,and generated NCO species.NCO species migrated to KIT-6 support and reacted with NO,generating N₂ and CO₂.In order to further broaden the reaction temperature window and low temperature catalytic activity,Ir-Rb/KIT-6 catalyst was prepared by doping alkali metal Rb on Ir/KIT-6.CO-SCR results showed that the activity of Ir-Rb/KIT-6 catalyst was significantly higher than Ir/KIT-6.When the loading amount of Rb was 1 wt.%,the low temperature of Ir-Rb1/KIT-6 was obviously impoved,and the temperature window was broadened.Ir-Rb1/KIT-6 catalyst had good oxidation resistance,sulfur resistance and stability.XPS results showed that the doping of Rb can induce electron transfer from Rb⁺to Ir^δ+,which is beneficial to improving the content of Ir⁰.More Ir⁰ is in favor of CO-SCR reaction.In situ DRIFTS showed that CO and NO were adsorbed on Ir during CO-SCR reaction,forming Ir-CO,NO₂,nitrite and other species.NO₂and nitrite can react with Ir-CO to form NCO.Then NCO react with NO to form N₂ and CO₂.The introduction of SO₂ can accelerate the reaction rate of NCO and NO.In addition,the presence of O₂ can promote the production of intermediate species NCO at low temperature,thus significantly enhancing the low temperature activity of Ir-Rb1/KIT-6.