DFT modeling of the hydrolysis of isocyanic acid over the TiO_2 anatase (101) surface: Adsorption of HNCO species

摘要

The nature of the interaction of isocyanic acid (HNCO) with the active centers at the ideal anatase TiO_2 (101) 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 (101) surface -dissociative and molecular adsorption. Only molecular adsorption of HNCO leads to the direct weakening and further splitting of the N=C bond, whichis 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 (101) 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.