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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.

The solidification microstructures of three nine-element Zr-Ni-based AB 2 type C14/C15 Laves hydrogen storage alloys are determined. The selected compositions represent a class of alloys being examined for usage as an MH electrode in nickel metal-hydride batteries that often have their best properties in the cast state. Solidification is accomplished by dendritic growth of hexagonal C14 Laves phase, peritectic solidification of cubic C15 Laves phase, and formation of cubic B2 phase in the interdendritic regions. The B2 phase decomposes in the solid state into a complex multivariate platelike structure containing Zr-Ni-rich intermetallics. The observed sequence C14/C15 upon solidification agrees with predictions using effective compositions and thermodynamic assessments of the ternary systems, Ni-Cr-Zr and Cr-Ti-Zr. Experimentally, the closeness of the compositions of the C14 and C15 phases required the use of compositional mapping with an energy dispersive detector capable of processing a very high X-ray flux to locate regions in the microstructure for quantitative composition measurement and transmission electron microscope examination.