Ab initio DFT study of urea adsorption and decomposition on the ZnO surface

The mechanisms of urea decomposition into isocyanic acid (HNCO) and ammonia (NH3) in gas-phase and on the ZnO ( 1 0 1 ¯ 0 ) surface have been investigated by using density functional theory. In gas-phase, urea decomposes into HNCO and NH3 in one step, which is a concert reaction. However, on the ZnO ( 1 0 1 ¯ 0 ) surface urea is found to decompose gradually, in which urea molecule first adsorbs on the ZnO surface, followed by the NH and the NC bonds breaking, and eventually rebinds to form NH3 and HNCO. The presence of ZnO ( 1 0 1 ¯ 0 ) surface decreases the energy barrier of urea decomposition. And as the intense interaction between the surface and urea, urea decomposition is exothermic by 48.0 kcal/mol on the surface, which is endothermic by 22.0 kcal/mol in the gas-phase.