JOSEPH A. FOURNIER, CHRISTOPHER J. JOHNSON, CONRAD T. WOLKE, ARRON B. WOLK, CHRISTOPHER M. LEAVITT, KRISTEN J. BREEN AND MARK A. JOHNSON, DEPARTMENT OF CHEMISTRY, YALE UNIVERSITY, NEW HAVEN, CT 06520.
\noindent Two aspects of catalytic CO2 conversion to transportable fuels involve understanding the local interactions between CO2 and the solvent mediating the reduction and the coordination of CO2 onto the organometallic framework that executes the chemical transformation. To address why ionic liquids are emerging as the solvents of choice for the catalysis, we first explore how CO2 attaches to two archetypal ionic liquid components: imidazole (Im) and acetate (Ac-). Im was seeded in a CO2 pulsed free jet expansion forming Im(CO2-)(CO2)m (m=1-2) clusters. Previous studies with pyridine revealed C-N bond formation between CO2- and pyridine with m=5 or 7, evidenced by the observation of a C-N stretch in the vibrational spectra. No such C-N bond formation is observed with Im; the CO2- appears to be hydrogen bonded to the Im N-H in an ion-molecule complex. Attachment to Ac- was studied by predissociation of the Ac-(CO2)m (m=1-4) clusters and, for m=1-3, a single peak assigned to the CO2 asymmetric stretch is observed near that of bare CO2, suggesting that the CO2 molecules are weakly bound adducts. However, the combination bands 2
3 in the 3600-3750cm-1 region reveal two distinct binding sites: a neutral site and a red-shifted, more perturbed site. For m=4, a red-shifted CO2 asymmetric stretch is observed, perhaps indicating the beginning of solvent mediated activation of a CO2 adduct. \bigskip
\noindent Finally, the CO2 reduction catalyst Ni(cyclam)2+ has been investigated using an electrospray ionization source coupled to a cryogenically cooled ion trap. By adding CO2 to the He buffer gas used to collisionally cool the ions in the trap, we have been able to condense up to five CO2 molecules onto Ni(cyclam)2+ at a trap temperature of 100K. The cryogenic ion vibrational predissociation (CIVP) spectra show the CO2 molecules to be acting as neutral adducts. We are now working to develop a method to generate and isolate the reactive Ni(cyclam)+ and capture the bound-CO2 intermediate.