Adsorption of CO2 in metal organic frameworks of different metal centres: Grand Canonical Monte Carlo simulations compared to experiments

A Grand Canonical Monte Carlo study has been performed in order to compare the different CO₂ adsorption mechanisms between two members of the MIL-n family of hybrid metal-organic framework materials. The MIL-53 (Al) and MIL-47 (V) systems were considered. The results obtained confirm that there is a structural interchange between a large pore and narrow pore forms of MIL-53 (Al), not seen with the MIL-47 (V) material, which is a consequence of the presence of μ ₂-OH groups. The interactions between the CO₂ molecules and these μ ₂ OH groups mainly govern the adsorption mechanism in this MIL-53 (Al) material. The subsequent breaking of these adsorption geometries after the adsorbate loading increases past the point where no more preferred adsorption sites are available, are proposed as key features of the breathing phenomenon. After this, any new adsorbates introduced into the MIL-53 (Al) large pore structure experience a homogeneous adsorption environment with no preferential adsorption sites in a similar way to what occurs in MIL-47 (V).     

SCTA and Adsorbents

Sample controlled thermal analysis (SCTA) can be used in several manners with respect to adsorbents. Almost 70% of adsorbent synthesis procedures involve a thermal step that can be adapted to a sample controlled method. In this respect, SCTA has been used for the preparation of activated alumina, calcination of zeolites and activation of carbons. The thermodesorption of adsorbed molecules can also be carried out using a sample controlled method. Here, both the surface area and pore volume of adsorbents can be assessed. Finally, SCTA can be highly beneficial in the thermal pretreatment of adsorbents prior to adsorption. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,Spectroscopy, and Hydroformylation Activity of Sterically Demanding,Phosphite‐Modified Cobalt Catalysts

The dinuclear complex [Co₂(CO)₆{P(O‐2,4‐t‐Bu₂C₆H₃)₃}₂] ( 6 ) has been synthesised and fully characterised. X‐Ray crystal‐structure analysis revealed a trans‐diaxial geometry, no bridging carbonyls, and Co? Co and Co? P bond lengths of 2.706(5) and 2.134(4) Å, respectively. The hydroformylation of pent‐1‐ene in the presence of 6 was studied at 120–180° at pressures between 20 and 80 bar Syngas. High‐pressure (HP) spectroscopy (IR, NMR) was used to detect potential hydride intermediates. HP‐IR Studies revealed the formation of [CoH(CO)₃{P(O‐2,4‐t‐Bu₂C₆H₃)₃}] ( 2 ) at ca. 105°, with no significant amount of [CoH(CO)₄] detectable. The intermediate 2 was synthesised and characterised. The formation of the undesired complex [CoH(CO)₂{P(O‐2,4‐t‐Bu₂C₆H₃)₃}₂] was completely suppressed due to the large cone angle of the sterically demanding phosphite.     

Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs

The hydrogen adsorption capacity and heat of adsorption at 77 K have been evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti) and UiO-66(Zr)), as well as in their -NH(2) and -(CF(3))(2) functionalized isoreticular structures. The capacity of hydrogen is basically related to the textural properties of the solids and not to their composition. The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol(-1)), except for the UiO-66(Zr) and MIL-53(Fe)-(CF(3))(2) analogues, whereas the presence of Lewis acid sites and/or a confinement effect enhances significantly the strength of interaction with hydrogen.