Understanding Trends in the NO Oxidation Activity of Single-Atom Catalysts

Nitric oxide (NO) emitted by coal-fired power plants causes severe environmental pollution. Catalytic oxidation of NO to NO2 is a promising technology to reduce NO pollution. However, the NO oxidation capacities of conventional catalysts were usually insufficient at a low temperature due to the difficulty to activate molecular oxygen (O2). Herein, single-atom catalysts (SACs) with high O2 activation capacities are proposed for NO oxidation. To design optimal SACs, we explicitly analyzed eight 3d transition metal SACs using spin-polarized density functional theory calculations with van der Waals corrections (DFT+D3), transition state analysis, scaling relation analysis, reaction descriptor analysis, and microkinetic modeling. For the first time, we derived a volcano-shaped microkinetic model to unravel the activity trends in the NO oxidation of SACs as a function of oxygen adsorption energy. This model shows that a Fe1-N4-C structure possesses the best performance for NO oxidation among the 75 analyzed SACs, in excellent agreement with recent pioneering experimental studies. Based on this volcano model, we screened the rest of the SACs with a Metal1-N4-C structure and provided important design guidelines for NO oxidation catalysts.