For FeSA-N3-C, the optimal reaction path for catalytic oxidation of HCHO is shown in For FeSA-N4-C, the optimal reaction path for catalytic oxidation of HCHO is shown in The relative energy changes of the best paths for three catalysts are shown in Figure . For FeSA-N3-C, the rate-determining step of catalytic oxidation is the process from IM6 to IM7, with an energy barrier of 1.09 eV. Subsequently, the productions of CO2 and H2O desorbs from FeSA-N3-C with 0.36 and 0.53 eV, respectively. For FeSA-N4-C, the rate-determining step of catalytic oxidation is the process from IS1 to IM1, with an energy barrier of 0.66 eV. The energies at which CO2 and H2O produced by reaction detach from FeSA-N4-C surface are 0.36 and 0.53 eV respectively.