|
Abstract
|
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. The doping of Al atoms significantly improves the surface reactivity and stability of (Zn12O12)n clusters. It is revealed that O2 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 O2 adsorption energy, although the amount of increase reduces as the cluster size grows. The adsorption energies of O2 over Al-doped (Zn12O12)n clusters range from -1.83 to -2.14 eV, which are more negative than those of CO molecule (≈-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 + Oads) are around 0.30 eV, which are substantially lower than the energy barriers in the ER process. Also, these energy barriers are comparable to, or even lower than, those seen on noble metals. Based on these findings, Al-doped ZnO clusters are proposed as efficient and novel CO oxidation catalysts.
|