DFT study of the effect of Ca on NO heterogeneous reduction by char

The effect mechanism of Ca on nitric oxide (NO) heterogeneous reduction by char was investigated using density functional theory calculations with correction of London dispersion interaction. Non-catalytic heterogeneous reduction of NO by char was also studied for comparison. Electron spin density and dual descriptor of the simplified char model with zigzag configuration were analyzed to predict adsorption sites of the NO molecule and Ca atom. It was found with the method of reduced density gradient that the calcium atom and carbon atoms at the edge of char were mainly combined by electrostatic attraction. The activation energy of each elementary reaction in the two reaction pathways indicated that Ca showed catalytic activity in the formation of N-N bond and the desorption of N-2 molecule. The fitted reaction activation energy was 76.34 kJ/mol for NO heterogeneous reduction at the edge of pristine char; whereas it was 51.78 kJ/mol for that at the edge of Ca-decorated char. Calculation results also showed that the addition of Ca could shorten the reaction path of NO heterogeneous reduction. The promotion of Ca to NO heterogeneous reduction was attributed to combination of the two aspects above.