全球CO2排放量在过去几个世纪迅速上升，尤其是最近几十年，CO2排放量的提高加剧了温室效应。CO2排放主要来自化石燃料燃烧，特别是燃煤发电厂。钙循环，即CaO的碳酸化/煅烧循环，是燃煤电厂最有前景的CO2捕集技术之一。同时，燃煤发电厂也是NOx排放的主要来源之一。由于具有成本低、毒性小等优点，CO可以作为NO的还原剂。CaO对于CO还原NO具有催化作用。煅烧炉中CaCO3分解所需的能量由生物质燃烧提供。一些未燃尽的焦炭随CaO流入碳酸化炉，与烟气中的O2反应生成CO。因此，在钙循环的碳酸化炉内捕集CO2的同时可实现NO脱除。但关于CaO在碳酸化阶段催化CO还原NO的微观反应机理尚不清楚。利用密度泛函理论(DFT)计算研究了钙循环碳酸化阶段CaO催化CO还原NO的机理，确定了CaO(100)表面上CO和NO分子的结构、吸附和反应路径参数，包括原子布局、键长、吸附能和能垒。CO和NO分子在CaO(100)表面的最佳吸附位是O-top位，吸附能分别为−0.35和−0.79 eV。在CO2存在下，CaO(100)表面上CO、NO的吸附能分别为−0.36、−0.20 eV。CO和NO分子在CaO(100)表面上共吸附是可行的，但CO2对共吸附有明显抑制作用。在CaO(100)表面进行的CO还原NO反应路径，在经历CO2形成与吸附、N2形成这2个基元反应后，最终生成1个N2分子与3个${rm{CO}}_3^{2-} $，总能垒为11.08 eV。其中，CO2形成及吸附(R→IM1→IM2)为整个反应过程的决速步骤。

Global CO2 concentration rapidly increases over the past few centuries, particularly in recent decades, and the greenhouse effect is sharply accelerated by the increase of CO2 emissions. CO2 emissions are mainly produced from fossil fuel combustion, in particular coal-fired power plants. Calcium looping, i.e. the carbonation/calcination cycles of CaO, is one of the most promising CO2 capture technologies for coal-fired power plant. At the same time, coal-fired power plants are also one of the main sources of NOx emissions. CO can be used as a reducing agent for NO due to its low cost and low toxicity. CaO is a suitable catalyst for NO reduction by CO. The combustion of biomass is used to provide the required energy for the decomposition of CaCO3 in the calciner. Few unburned char and CaO flow into the carbonator, where the unburned char reacts with O2 in the flue gas to generate CO. Thus, the simultaneous NO removal and CO2 capture in the carbonator of the calcium looping process can be realized. However, the reaction mechanism of the effect of CaO on NO removal by CO in the carbonation stage is unclear. The mechanism of NO reduction with CO catalyzed by CaO in the carbonation stage is investigated by the density functional theory (DFT) calculations. The structural, adsorption, and reaction path parameters, including atomic layout, bond length, adsorption energy, and energy barrier of CO and NO molecules on the CaO (100) surface, are determined. The optimal adsorption sites of CO and NO molecules on the CaO (100) surface are O-top sites, and the adsorption energies are −0.35 and −0.79 eV, respectively. The CO and NO adsorption energies on the CaO (100) surface in the presence of CO2 are −0.36 and −0.20 eV, respectively. The co-adsorption of CO and NO molecules appears feasible on the CaO (100) surface, while CO2 exhibits obvious inhibition for the co-adsorption. The reaction path of NO reduction by CO on the CaO (100) surface undergoes two elementary reaction stages: CO2 formation and adsorption, and N2 generation. Finally, one N2 molecule and three ${rm{CO}}_3^{2-} $ ions are formed, with a total energy barrier of 11.08 eV. CO2 formation and adsorption (R→IM1→IM2) are the rate-determining steps of the whole reaction process.

山东省自然科学基金重点资助项目(ZR2020KE042)；国家自然科学基金联合基金重点资助项目(U22A20435)

初雷哲，柴守冰，李英杰. 钙循环碳酸化过程CaO催化CO脱除NO的DFT研究[J]. 煤炭学报，2023，48(11)：4205−4212.

CHU Leizhe，CHAI Shoubing，LI Yingjie. DFT study on NO reduction with CO catalyzed by CaO in carbonation stage of calcium looping process[J]. Journal of China Coal Society，2023，48(11)：4205−4212.