Low-temperature oxidation of methane mediated by Al-doped ZnO cluster and nanowire: a first-principles investigation.

Context: First-principles calculations are performed to investigate the catalytic oxidation of methane by using NO as an oxidizing agent over aluminum (Al)-doped ZnO cluster and (ZnO) nanowire. The impact of Al impurity on the geometry, electronic structure, and surface reactivity of ZnO and (ZnO) is thoroughly studied. Our study demonstrates that Al-doped ZnO systems have a better adsorption ability than the corresponding pristine counterparts. It is found that NO molecule is initially decomposed on the Al site to provide the N molecule, and an Al-O intermediate which is an active species for the CH oxidation. The conversion of CH into CHOH over AlZnO and (AlZnO) requires an activation energy of 0.45 and 0.29 eV, respectively, indicating it can be easily performed at normal temperatures. Besides, the overoxidation of methanol into formaldehyde cannot take place over the AlZnO and (AlZnO), due to the high energy barrier needed to dissociate C-H bond of the CHO intermediate.

Method: Dispersion-corrected density functional theory calculations were performed through GGA-PBE exchange-correlation functional combined with a numerical double-ζ plus polarization (DNP) basis set as implemented in DMol. To include the relativistic effects of core electrons of Zn atoms, DFT-semicore pseudopotentials were adopted. The DFT + D scheme proposed by Grimme was used to involve weak dispersion interactions within the DFT calculations. The reaction energy paths were generated by the minimum energy path calculations using the NEB method.