Dong Changqing

Reaction Activity and Deep Reduction Reaction Mechanism of a High Index Iron Oxide Surface in Chemical Looping Combustion

The possibility of morphological control of iron oxide as an oxygen carrier for chemical looping combustion was investigated using density functional theory and experiment. First, we calculated the reactivity of Fe2O3 with highindex facets [104] and lowindex facets [001], as well as the deep reduction reaction mechanism of these two facets. Surface reaction results show that the activity of Fe2O3[104] for oxidizing CO is greater than that of Fe2O3[001]. Fe2O3[104] was reduced into iron oxide at lower oxidation state or into iron, which could then be regenerated after being oxidized by O2. The deep reduction reaction mechanism between oxygen carrier and CO shows that Fe2O3[104] can be completely reduced into Fe, and Fe2O3[104] exhibits high oxygen transfer ability. However, Fe2O3[001] can only be reduced to a limited extent, with a high energy barrier preventing further reduction, while it also exhibits limited oxygen transfer capacity. Results of experiments further verify the high reactivity and stability of Fe2O3[104].

Fe 2 O 3 (1-12) 作用下CO化学链燃烧反应机理研究

在化学链燃烧（CLC）过程中，载氧体表面的原子结构和电子特性决定了其化学反应活性.本文以Fe2O3为载氧体，探讨了其自然条件下主要裸露的高米勒数指表面（1-1 2）的结构性质，研究发现表面不同配位数的氧和铁原子（包括O2f、O3f、O4f、Fe4f和Fe5f）的键参数、电子态密度及电荷布居等存在明显差异.为探究这种差异对Fe2O3反应活性的影响，对比分析了CO在表面5种氧和铁原子位生成CO2的吸附-反应机理.CO在表面低配位O原子O2f和O3f首先形成物理吸附，然后被晶格氧氧化生成CO2，反应需要克服能垒分别为3.657 eV和3.401 eV；然而，CO在O4f位吸附时，首先克服1.864 eV能垒形成二齿形碳酸盐物种，之后克服1.097 eV的能垒形成CO2.当CO在Fe4f和Fe5f位吸附时，CO与Fe原子成键，后经过活化与表面O原子成键，形成二齿形碳酸盐物种，能垒分别为0.416和0.219 eV，最终碳酸盐物种分别克服0.500和1.462 eV的能垒生成CO2.因此，可以推断表面高配位数的O4f、Fe4f和Fe5f原子，由于其较高的氧化态，在化学链燃烧过程中充当活性位的作用.本研究有助于了解铁基载氧体表面化学链燃烧反应的微观机理，并为载氧体表面结构性能调控制备提供理论借鉴.