Nitric oxide (NO) emitted from coal-fired power plants has raised global concerns. The catalytic oxidation of NO is a promising technology for NO removal. Due to its high selectivity and high catalytic activity, a single-atom iron catalyst supported on a single-vacancy (SV) graphene-based substrate (Fe/SV) may be a promising catalyst for NO oxidation. The adsorption characteristics and reaction mechanisms of NO and O₂ on the surface of Fe/SV were systematically studied through density functional theory calculation. The detailed reaction paths under the Langmuir–Hinshelwood, Eley–Rideal and termolecular Eley–Rideal reaction mechanisms were investigated, and thermodynamic and kinetic analyses were performed to study the effect of reaction temperature on the reaction rate and equilibrium. It is found that there are six different reaction paths which can be divided into two reaction patterns, step-by-step and simultaneous. The minimum activation energy of NO oxidation is only 0.04 eV and Eley–Rideal seems to be the dominant reaction mechanism of NO oxidation in flue gas. The reaction temperature has an obvious promoting effect on the reaction rate and an inhibitory effect on the reaction equilibrium. We hope that this research can lay a foundation for further theoretical research on NO oxidation and provide a guideline for experimental investigation on NO oxidation.

The high efficiency of organic–inorganic hybrid perovskites has attracted the attention of many scholars all over the world, the chemical formula of which is ABX₃, where A is an organic cation, B is a metal cation, and X is a halogen ion. In addition, the micro-mechanism behind the efficient photoelectric conversion needs more in-depth exploration. Therefore, in this work, based on time-dependent density functional theory (TD-DFT), the electron transfer mechanism from the ground state to the first singlet excited state was systematically investigated by electron and hole analysis and an inter-fragment charge transfer amount method (IFCT). In this work, we optimized and analyzed 99 different perovskite cluster configurations, where A sites are CH₃NH₃ ⁺ (MA⁺), NH₂CHNH₂ ⁺ (FA⁺), CH₃CH₂NH₃ ⁺ (EA⁺), NH₂CHOH⁺ (JA⁺), NH₃OH⁺ (BA⁺), N(CH₃)₄ ⁺ (DA⁺), CH₃CH₂CH₂NH₃ ⁺ (KB⁺), CH₃CH₂CH₂CH₂NH₃ ⁺ (KC⁺), C₃N₂H₅ ⁺ (RA⁺), CH(CH₃)₂ ⁺ (TA⁺), and CH₃NH(CH₃)₂ ⁺ (UA⁺), B sites are Ge²⁺, Sn²⁺ and Pb²⁺, and X sites are Cl⁻, Br⁻ and I⁻. According to the analysis of a series of perovskite clusters of the hole–electron distribution, the distribution is mainly concentrated on BX, and electrons and holes are respectively distributed on B and X sites. The exciton binding energy decreases when the metal element changes from Ge to Pb and the halogen element changes from Cl to I. A radar chart including the exciton binding energy, excited energy, amount of net charge transfer, electron and hole overlap index, distance between the centroid of holes and electrons, and the hole and electron separation index was proposed to intuitively describe the electron transmission characteristics of perovskites. Based on that, a comprehensive score index was innovatively proposed to evaluate the photoelectric property of perovskites, providing foundational guidance for the design of high-efficiency organic–inorganic hybrid perovskites.