Energy profiles by DFT methods for CO and NO catalytic adsorption over ZnO surfaces

It is known that a given material can exhibit different catalytic performances by deploying different crystal-lographic orientations on the surface, which can increase the reactivity of the system. This work is based on the experimental results of a previous work, where a ZnO thin film presented a (103) preferred orientation, raising the interest to investigate its catalytic performance on NO and CO by using DFT calculations. Three different conditions of the surface are considered in this work: a defect-free surface, pre-adsorption of O-2 and pre-adsorption of OH molecules. Calculations demonstrated that CO and NO catalytic reactions are improved primordially by the pre-adsorbed species on the material. ZnO (103) defect-free surface presents higher affinity to NO on the three tested sites. In the case of pre-adsorbed oxygen, the surface presented higher reaction energies for CO. In both conditions, the gases were oxidized to NO2 and CO2 respectively. In the case of pre-adsorbed OH radicals, the final products were nitrous acid (HNO2) and carboxyl groups (COOH), bonded to the surface with different energies depending on the adsorption site. ZnO (103) surface proved to be reliable for using it in reactions involving pre-adsorbed oxygen and OH molecules.

Automated summary

The study shows that different crystallographic orientations on the surface of a material can affect its catalytic performance. Pre-adsorption of oxygen and hydroxyl molecules on a ZnO (103) thin film was found to improve its catalytic reactions towards CO and NO. The surface also demonstrated higher affinity towards NO and CO under different conditions.