Understanding the atomic structure and the corresponding adsorption mechanism of CO₂ adsorbents is the key to develop efficient CO₂ adsorption materials. Here, we studied hydrotalcite-derived oxides or layered double oxides (LDOs), one of the most promising candidates for the inexpensive and effective CO₂ adsorption in the intermediate temperature regime, using atomistic simulation techniques. We first constructed the equilibrium structure of an LDO and showed that this oxide was crystalline with an MgO-like structure. In particular, Mg ions configured with the FCC arrangement of oxygen ions and most of the Al³⁺ ions occupied octahedral positions by substituting Mg²⁺ ions and the rest (∼10%) occupied the tetrahedral positions. We then compared the CO₂ physisorption properties of the amorphous and crystalline LDOs that respectively represented LDOs form at lower and higher limits of hydrotalcite calcination. Static and dynamic adsorption analyses revealed that the amorphous LDO had overall higher physisorption capacity. CO₂ molecules exhibited a random arrangement in the adsorption layer of the amorphous LDO but an ordered arrangement in the case of crystalline LDO. As a result, CO₂ molecules were able to adsorb to and to desorb from the amorphous LDO surface dynamically while the stable adsorption layer near the crystalline LDO surface acted like a contamination preventing other CO₂ molecules to adsorb, thereby lowering the overall adsorption capacity of the crystalline LDO. Depending on the level of crystallinity, the physisorption behavior of the mixed oxide forming during the hydrotalcite calcination is expected to change between two structures studied here.

了解CO ₂吸附剂的原子结构和相应的吸附机理是开发高效的CO ₂吸附材料的关键。在这里，我们使用原子模拟技术研究了水滑石衍生的氧化物或层状双氧化物（LDOs），它们是中温条件下廉价有效吸附CO ₂的最有希望的候选者之一。我们首先构建了LDO的平衡结构，并表明该氧化物是具有MgO样结构的晶体。特别是，配置有氧离子FCC排列的Mg离子和大多数Al ³⁺离子通过取代Mg ²⁺占据八面体位置离子和其余（约10％）占据四面体位置。然后，我们比较了分别代表在水滑石煅烧的下限和上限下形成的LDO的无定形和结晶LDO的CO ₂物理吸附特性。静态和动态吸附分析表明，无定形LDO总体上具有较高的物理吸附能力。CO ₂分子在无定形LDO的吸附层中显示出无规排列，但在结晶LDO的情况下显示出有序排列。结果，CO ₂分子能够动态地吸附到非晶LDO表面和从非晶LDO表面解吸，而靠近晶体LDO表面的稳定吸附层则起到了防止其他CO ₂污染的作用。分子被吸附，从而降低了晶体LDO的总体吸附能力。根据结晶度的高低，预计在水滑石煅烧过程中形成的混合氧化物的物理吸附行为将在此处研究的两种结构之间发生变化。