Accelerating Nitrite Reduction to Ammonia: The Synergistic Effect of Dual Active Site Pt–Ir Catalysts

Ir-based catalysts have been demonstrated as promising catalysts for the reduction of NO2- to ammonia (NRA). However, the strong competitive adsorption of NO2- over H2 on Ir sites, leading to H* deficiency at high NO2- concentrations, would hinder its real application. Here, we proposed an effective strategy to solve this problem by constructing dual active site Ir-Pt/TiO2 composite catalysts with physical mixing (Ir+Pt/TiO2) and co-impregnation (IrPt/TiO2) methods. On such catalysts, the hydrogen spillover effect on Pt sites could alleviate H* insufficiency on Ir sites, thereby accelerating the NRA reaction. Specifically, the optimal dry-mixed Ir+Pt/TiO2 catalyst exhibited an NRA rate constant of 12.4 L·gIr+Pt-1·min-1, approximately twice that of the Ir/TiO2 sample. Moreover, Ir+Pt/TiO2 catalysts showed first-order reaction kinetics rather than competitive reaction kinetics, confirming the alleviation of the H* deficiency limitation. Various characterization methods revealed that H* derived from H2 dissociated adsorption on Pt sites could migrate through the TiO2 support to Ir sites. DFT calculations also proved the thermodynamic feasibility of H* migration on TiO2. Moreover, to further improve NRA activity, IrPt/TiO2 alloy catalysts were employed to enhance Pt-Ir synergy, exhibiting the highest NRA rate constant of 17.0 L·gIr+Pt-1·min-1.