DFT study of coverage-depended adsorption of NH3 on TiO2-B (100) surface

Abstract

A previous study showed that TiO₂-B (100) surface is very unique. It is characterised by high activity and a loose structure. In this study, we studied the adsorption of ammonia on TiO₂-B (100) surface at coverages ranging from 1/6 ML to 1 ML using ab initio density functional calculations. We also investigated the adsorption of an isolated ammonia molecule on TiO₂-B (001) surface to compare the different activities of TiO₂-B (100) and (001) surfaces towards NH₃. The results showed that the TiO₂-B (100) surface is more reactive towards NH₃ molecule than TiO₂-B (001) surface, and the Lewis acid site on TiO₂-B (100) surface is more acidic. The decrease rate of the average molecular adsorption energy of NH₃ with coverage on TiO₂-B (100) surface is substantially lower than that on a rutile (011) surface above 1/2 ML coverage due to the open structure of TiO₂-B (100) surface. The average molecular adsorption energy shows a linear dependence on the coverage of y = 111.0 − 36.3x on TiO₂-B (100) surface. The possibility of NH₃ molecule onto the Ti_5c site is nearly equal to forming a dimer with adsorbed NH₃ on TiO₂-B (100) surface at 5/6 ML coverage.