Steven S. Kaye

Evaluation of cation-exchanged zeolite adsorbents for post-combustion carbon dioxide capture

A series of zeolite adsorbents has been evaluated for potential application in post-combustion CO2 capture using a new high-throughput gas adsorption instrument capable of measuring 28 samples in parallel. Among the zeolites tested, Ca-A exhibits the highest CO2 uptake (3.72 mmol g−1 and 5.63 mmol cm−3) together with an excellent CO2 selectivity over N2 under conditions relevant to capture from the dry flue gas stream of a coal-fired power plant. The large initial isosteric heat of adsorption of −58 kJ mol−1 indicates the presence of strong interactions between CO2 and the Ca-A framework. Neutron and X-ray powder diffraction studies reveal the precise location of the adsorption sites for CO2 in Ca-A and Mg-A. A detailed study of CO2 adsorption kinetics further shows that the performance of Ca-A is not limited by slow CO2 diffusion within the pores. Significantly, Ca-A exhibited a higher volumetric CO2 uptake and CO2/N2 selectivity than Mg2(dobdc) (dobdc4− = 1,4-dioxido-2,5-benzenedicarboxylate; Mg-MOF-74, CPO-27-Mg), one of the best performing adsorbents. The exceptional performance of Ca-A was maintained in CO2 breakthrough simulations.

Generation and O2 Adsorption Studies of the Microporous Magnets CsNi[Cr(CN)6] (Tc =75 K) and Cr3[Cr(CN)6]2·6H2O (TN = 219 K)

Dehydration of the Prussian blue analogues CsNi[Cr(CN)(6)] x 2 H(2)O (1) and Cr(3)[Cr(CN)(6)](2) x 10 H(2)O (2) affords two new microporous magnets: CsNi[Cr(CN)(6)] (1d) and Cr(3)[Cr(CN)(6)](2) x 6 H(2)O (2d). Compounds 1d and 2d maintain the Prussian blue structure, and N(2) adsorption measurements at 77 K show them to be microporous with BET surface areas of 360 and 400 m(2)/g, respectively. Both solids largely retain the magnetic properties of their parent hydrates, with 1d ordering at 75 K and 2d ordering at 219 K, by far the highest ordering temperature yet observed for a microporous magnet. The compounds further show unexpected changes in their magnetic properties upon adsorption of O(2). In 2d, adsorption of O(2) results in a reversible decrease in the magnetic moment of the system, as well as a reduction of the coercivity from 110 to 10 G and of the remnant magnetization from 1200 to 400 emu.G/mol, indicating a net antiferromagnetic interaction between O(2) and the framework. In 1d, adsorption of O(2) instead results in a reversible increase in the magnetic moment of the system, indicating a net ferromagnetic interaction between O(2) and the framework. Together, the results suggest that ferromagnetic exchange coupling between O(2) and the [Cr(CN)(6)](3-) units provides the predominate magnetic interaction of the adsorbate with the framework.

Hydrogen adsorption in dehydrated variants of the cyano-bridged framework compounds A2Zn3[Fe(CN)6]2·xH2O (A = H, Li, Na, K, Rb)

The impact of coordinatively-unsaturated alkali-metal ions on hydrogen adsorption is studied in dehydrated variants of the compounds A(2)Zn(3)[Fe(CN)(6)](2).xH(2)O (A = H, Li, Na, K, Rb), revealing maximum adsorption enthalpies that vary from 7.7 kJ mol(-1) for A = Na to 9.0 kJ mol(-1) for A = K.