Removal of reactive organic species from the environment is often done using catalytic centers. Apart from the activity of the catalyst, the material availability and the cost of production of the catalyst are important. Here, several inexpensive materials are investigated as potential catalysts for toluene degradation.
Toluene adsorption on MnO2, Mn2O3, Fe2O3, NiO and CuO was theoretically investigated. Unit cell has been formed from crystal slab of approximately 1000 atoms surrounded by vacuum layer to which toluene and oxygen molecules were added. The reactive force-field (ReaxFF) method was used. Temperature controlled Berendsen thermostat (NVT) is applied for 2.5fs molecular dynamics (MD) calculation on energy minimized crystal structure. Toluene is added and additional 25ns MD calculation is performed at 500K. Calculations involving temperature rise from 500K to 700K, followed by 6.25fs calculation at 700K and temperature drop back to 500K were performed to model much longer time available under experimental conditions.
The catalyst potential for toluene adsorption and catalytic activity is evaluated by the amount of free toluene molecules as function of time. It is found that the structures investigated showed behavior which is related to the O2 and toluene binding energies. The largest catalytic activity is observed for Fe2O3 and MnO2, while CuO did not show any toluene adsorption or degradation. While Fe2O3 activity seems to be the result of large toluene adsorption energy, MnO2 structure additionally offers crystal surface oxygen and show the contribution to the activity from surface dynamics and structure (including oxygen diffusion, defects, etc.).