Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Am Chem Soc. 2012 May 9;134(18):7944-51. doi: 10.1021/ja3014133. Epub 2012 Apr 26.
The development of sorbents for next-generation CO(2) mitigation technologies will require better understanding of CO(2)/sorbent interactions. Among the sorbents under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies of reduced dimensionality. We have characterized the non-equilibrium CO(2) sorption of OMS-2, a well-known one-dimensional microporous octahedral molecular sieve with manganese oxide framework. Remarkably, we find that the degree of CO(2) sorption hysteresis increases when the gas/sorbent system is allowed to equilibrate for longer times at each pressure step. Density functional theory calculations indicate a "gate-keeping" role of the cation in the tunnel, only allowing CO(2) molecules to enter fully into the tunnel via a highly unstable transient state when CO(2) loadings exceed 0.75 mmol/g. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO(2) is responsible for the observed hysteretic behavior.
为了开发下一代 CO(2)减排技术的吸附剂，我们需要更好地了解 CO(2)/吸附剂之间的相互作用。在考虑的吸附剂中，有一种是具有降低维度的分级孔形态的选择形状的微孔分子筛。我们已经对 OMS-2 的非平衡 CO(2)吸附进行了特征描述，OMS-2 是一种具有氧化锰骨架的知名一维微孔八面体分子筛。值得注意的是，我们发现当气体/吸附剂系统在每个压力步骤下允许更长时间达到平衡时，CO(2)吸附滞后的程度会增加。密度泛函理论计算表明，在隧道中的阳离子起着“把关”的作用，只有当 CO(2)负载超过 0.75mmol/g 时，CO(2)分子才能通过高度不稳定的瞬态完全进入隧道，从而允许 CO(2)分子进入。与把关效应相关的能量障碍表明了一种吸附机制，其中 CO(2)的动力学捕获是导致观察到的滞后行为的原因。
