NH₃ adsorption on the brönsted and Lewis acid sites of V₂O₅(010): A periodic density functional study

This paper deals with the adsorption states of ammonia on both the Brönsted and Lewis acid sites of V₂O₅-(010) surface using the periodic boundary first-principles density functional (DFT) calculations. The calculated results indicate that ammonia adsorption takes place on both the Brönsted and Lewis sites of V₂O₅ surface, whereas the adsorption on the Brönsted 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 Brönsted sites, it is found that the H-bonding plays a crucial role and that the ammonium species was formed when NH₃ 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.