The effect of nitrogen doping on mercury oxidation/chemical adsorption on the CuCo2O4(110) surface: a molecular-level description

Abstract

Based on density functional theory (DFT) calculations, the detailed mercury oxidation/chemical adsorption mechanisms on the N-doped CuCo₂O₄(110) surface are studied. The DFT calculations show that O_w (bonded with one Cu²⁺ ion and one Co³⁺ ion) is far more active than O_s (bonded with three Co³⁺ ions) and the mercury oxidation/chemical adsorption activation energy (E_a) on the virgin CuCo₂O₄(110) surface involving O_w is 0.85 eV. The physically adsorbed mercury overcomes the E_a and enters the energy well that plays an important role in mercury oxidation/chemical adsorption. Nitrogen doping can greatly increase the activity of O_w and decrease the activity of O_s at the same time, which greatly affect the mercury oxidation/chemical adsorption abilities on the CuCo₂O₄(110) surface, and the E_a variation of mercury oxidation/chemical adsorption is as follows: 0.85 eV (virgin CuCo₂O₄(110)) → 0.76 eV (one N-doped CuCo₂O₄(110)) → 0.69 eV (two N-doped CuCo₂O₄(110)) → 0.48 eV (three N-doped CuCo₂O₄(110)). In addition, N-doping can decrease the adsorption energy of mercury and mercuric oxide. The effect of N-doping on the bonding mechanism of mercury adsorption on the CuCo₂O₄(110) surface is analyzed by the local density of state (LDOS) and the natural bonding orbital (NBO). The calculation results correspond well to the experimental data.