NH_3 adsorption on the Bronsted and Lewis acid sites of V_2O_5(010): A periodic density functional study

摘要

This paper deals with the adsorption states of ammonia on both the Bronsted and Lewis acid sites of V_2O_5-(010) surface using the periodic boundary first-principles density functional (DFT) calculations. The calculated results indicate that ammonia adsorption takes place on both the Bronsted and Lewis sites of V_2O_5 surface, whereas the adsorption on the Bronsted sites is found to be more favorable energetically. It is observed that ammonia adsorbs on the Lewis sites with different coverages, whereas stability under high coverage is low due to the steric repulsion derived from the coadsorbed ammonia molecules. In both the cases, it shows that the coordination interaction and hydrogen bonding between the N-H and vanadyl oxygen contributes to the binding energy. As for the adsorption on the Bronsted sites, it is found that the H-bonding plays a crucial role and that the ammonium species was formed when NH_3 adsorbs at the hydroxyl group containing the vanadyl oxygen. This is in agreement with the IR observations. Furthermore, it is confirmed that the hydroxyl group consisting of the vanadyl oxygen acts as the most reactive site for ammonia adsorption.