Material Exhibiting Efficient CO2 Adsorption at Room Temperature for Concentrations Lower Than 1000 ppm: Elucidation of the State of Barium Ion Exchanged in an MFI-Type Zeolite.

Carbon dioxide (CO2) gas is well-known as a greenhouse gas that leads to global warming. Many efforts have been made to capture CO2 from coal-fired power plants, as well as to reduce the amounts of excess CO2 in the atmosphere to around 400 ppm. However, this is not a simple task, particularly in the lower pressure region than 1000 ppm.

Success in making Zn+ from atomic Zn(0) encapsulated in an MFI-type zeolite with UV light irradiation.

For the first time, the paramagnetic Zn(+) species was prepared successfully by the excitation with ultraviolet light in the region ascribed to the absorption band resulting from the 4s-4p transition of an atomic Zn(0) species encapsulated in an MFI-type zeolite. The formed species gives a specific electron spin resonance band at g = 1.998 and also peculiar absorption bands around 38,000 and 32,500 cm(-1) which originate from 4s-4p transitions due to the Zn(+) species with paramagnetic nature that is formed in MFI.

Further evidence for the existence of a dual-Cu+ site in MFI working as the efficient site for C2H6 adsorption at room temperature.

We have recently clarified the following point: a dual-type site, which is composed of a pair of monovalent copper ions (Cu(+)) formed in a copper-ion-exchanged MFI-type zeolite (CuMFI), functions as the active center for strong ethane (C2H6) adsorption even at room temperature rather than a single-type site composed of a Cu(+) ion. However, the character of the dual-Cu(+) site in a CuMFI is not yet fully understood. In this study, we have elucidated the nature of the active sites for C2H6 based on infrared (IR) and calorimetric data.

Unprecedented reversible redox process in the ZnMFI-H2 system involving formation of stable atomic Zn(0).

In its element: Zn(2+) at the M7 site of MFI-type zeolites activates H(2), via ZnH and OH species, and leads to Zn(0) species. The Zn(0) species returns to its original state, a Zn(2+) ion, upon evacuation of the zeolite at 873 K (see picture). The formation of the Zn(0) species is supported by DFT calculations.

Behavior of Ag3 clusters inside a nanometer-sized space of ZSM-5 zeolite.

We found from DFT calculations that Ag-Ag orbital interactions as well as Ag-O electrostatic interactions determine the structures of three silver cations inside a nanometer-sized cavity of ZSM-5 (Ag(3)-ZSM-5) in lower and higher spin states. Both interactions strongly depend on the number of Al atoms substituted for Si atoms on the ZSM-5 framework (ZSM-5(Al(n))), where n ranges from 1 to 3. In smaller n, stronger Ag-Ag orbital interactions and weaker Ag-O electrostatic interactions operate.

Site-specific Xe additions into Cu-ZSM-5 zeolite.

Large-scale density functional theory (DFT) calculations found significant preferences of two-coordinated copper cations as Xe binding site in ZSM-5. Such site-preferences cannot be seen in usual adsorbents such as the CO or NO molecule inside Cu-ZSM-5 as well as the Xe atom inside alkali-metal exchanged ZSM-5s. A key factor in the specificity of the inner Xe atom is that interactions of the Xe atom with the extraframework copper cation are substantial relative to the extraframework alkali-metal cases, but weak relative to the CO and NO cases.