CoO–ZnO solid solution as a model to investigate the CO–cation interaction: an FTIR and HRTEM study

The IR spectra of CO adsorbed at 77 K on ZnO ex-carbonate (and for comparison on ZnO kadox), on CoO and on CoO–ZnO solid solution (containing 0.05 mole fraction of CoO) are reported. By diluting the cobalt ions within a ZnO matrix, we have designed a model solid where the Co2+ ions (having a d7 configuration and frontier orbitals with d character) emerging on the surface experience the same ionicity and coordinative situation as Zn2+(d10 configuration and frontier orbitals without d character). Consequently, the observed difference in the CO stretching vibrations of the Zn2+CO and Co2+CO surface complexes has been ascribed to differences in the d– overlap contributions. The increased d– overlap effects are also responsible for the strong increase in the permanent (µ00, µ11) and transition (µ01) dipole moments of CO adsorbed on Co2+ in ZnO, compared with those on Co2+ in the MgO matrix and also those of CO adsorbed on ZnO and MgO.