DFT modeling of the hydrolysis of isocyanic acid over the TiO 2 anatase (1 0 1) surface: Adsorption of HNCO species

Abstract

The nature of the interaction of isocyanic acid (HNCO) with the active centers at the ideal anatase TiO 2 (1 0 1) surface were studied using ab initio density functional theory (DFT) method with a cluster model. Two types of adsorption of isocyanic acid are found to be likely at (1 0 1) surface – dissociative and molecular adsorption. Only molecular adsorption of HNCO leads to the direct weakening and further splitting of the N C bond, which is a necessary step for the hydrolysis of isocyanic acid. During molecular adsorption of HNCO, an energetically stable intermediate surface complex is created with an adsorption energy of −1.33 eV, in which the HNCO skeleton is changing due to new strong bonds between C–O s and N–Ti s. Based on the existence of this intermediate complex a probable reaction pathway for the hydrolysis of HNCO over the ideal anatase (1 0 1) surface was developed. A surface oxygen vacancy was formed after the decomposition of the intermediate complex and CO 2 desorption. Afterwards, water adsorbs at the oxygen vacancy site and NH 3 is successively formed. The HNCO hydrolysis over TiO 2 was found to be energetically favorable with global energy gain of about −2.08 eV.