A Computational Study on Adsorption Configurations and Dissociative Reactions of the HN3 Molecule on the TiO2 Anatase (101) Surface

This study investigates the adsorption configurations and the dissociative reactions of HN3 on the TiO2 anatase (101) surface by first-principles calculations. The results show that there are six different adsorption configurations of HN3 adsorbed on the surface. Among those adsorption configurations, the most stable adsorbate configuration is side-on HN(N2)−Ti(a), with an adsorption energy of 10.2 kcal/mol. In addition, for the HN3 fragments, the most stable adsorbate is Ti−(H)N−O(a), with an adsorption energy of 69.8 kcal/mol. The effect of the H present in the coadsorbed configuration significantly increases the adsorption energy by 46.4, 44.2, and 49.2 kcal/mol for the adsorbates of N3−Ti(a), Ti−N3−O(a), and Ti−N3−Ti(a), respectively. The lowest two energy levels for dissociative adsorbates are Ti−(H)N−O(a) + N2−Ti(a) and N3−Ti(a)a + H−O(a), and their energies are 5.7 and −12.8 kcal/mol, respectively. In addition, for the latter dissociative adsorbates, the two lowest energy barriers for these adsorbates that transit from their initial end-to-end Ti−N3H···O*(a) and end-to-end Ti−N3H−O(a) are approximately 2.6 kcal/mol. The comparison made between HN3 on both anatase and rutile surfaces shows that the reactions of dissociative adsorptions of HN3 are endothermic for Ti−(H)N−O(a) + N2−Ti(a) and exothermic for N3−Ti(a)a + O−H(a) on the anatase (101) surface, while both are exothermic on the rutile (110) surface.