CO oxidation mediated by Al-doped ZnO nanoclusters: A first-principles investigation

Using density functional theory computations, the reaction pathways of CO oxidation mediated by Al-doped Zn12O12 cluster and its assembled wire-like (Zn12O12)(n=2-4) structures were studied. It is revealed that O-2 molecule is chemisorbed over the doped clusters while physisorbed over pristine (Zn12O12)(n). Moreover, increasing the size of the nanocluster from AlZn11O12 to (AlZn11O12)(4) enhances the O-2 adsorption energy, although the amount of increase reduces as the cluster size grows. The adsorption energies of O-2 over Al-doped (Zn12O12)(n) clusters range from -1.83 to -2.14 eV, which are more negative than those of CO molecule (approximate to-0.80 eV). The Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) pathways are used to investigate the oxidation mechanisms of the CO molecule. The energy barriers for the rate limiting step in the LH mechanism (i.e., OCOO -> CO2 + O-ads) are around 0.30 eV, which are substantially lower than the energy barriers in the ER process.