基于密度泛函理论的CuO氧载体释氧机理研究

Oxygen Release Mechanisms of Cu-Based Oxygen Carriers Based on Density Functional Theory Calculations

化学链氧解耦(CLOU)是基于化学链燃烧(CLC)技术的一种新型燃烧方式,具有CO2内分离的优良特性。具有良好吸氧释氧性能的氧载体是CLOU技术的关键,其宏观层面的反应性决定于其微观层面的晶格氧传输机理,但目前对这种微观机理的研究非常缺乏。本文采用量子化学计算方法——密度泛函理论(DFT)研究Cu O氧载体释氧的微观机理,构建了Cu O团簇及Cu O平板模型,模拟团簇及表面的释氧过程。Cu O平板模型释氧包括O原子在Cu O内部扩散、表面O2的形成及释放过程。结果表明:Cu O(111)表面释氧过程的最高能量势垒为3.16 e V,与实验值3.39 e V接近,低于Cu O团簇模型的释氧能量势垒3.51 e V;此外,O原子在Cu O(111)内部的扩散势垒仅为0.87 e V,说明Cu O(111)释氧的限制步骤是表面O2的形成过程。

Chemical-looping with oxygen uncoupling （CLOU） is a new combustion method based on chemical-looping combustion technology, which allows intrinsic separation of pure CO2 from hydrocarbon combustion. The key point of CLOU is finding an ideal oxygen carrier that has good oxygen adsorption and releasing characters. The reactivity of oxygen carriers in macro-level is determined by the mechanism of microscopic lattice oxygen transportation, but few attentions have been paid on the subject currently. This article used density functional theory （DFT） to study the oxygen release mechanism of CuO carriers, the CuO clusters and slab models were built to simulate the process of cluster and surface oxygen release. CuO slab model’s oxygen release process includes inward oxygen atom diffusion, the formation of O2 molecule in surface and the release of O2 molecule. The results indicate that the highest energy barrier during the CuO（111） surface oxygen release is 3.16 eV, which is close to the experiment value 3.39 eV, but lower than that of CuO cluster model. And besides, the energy barrier of oxygen atom diffusion inside the CuO（111） is just 0.87 eV, indicating that the surface oxygen molecules’ formation process is the rate-limit step of CuO（111） oxygen release.