First principle study of adsorption and desorption behaviors of NH3 molecule on the TaC (0001) surface

Abstract

The adsorption and desorption behaviors of ammonia on TaC(0001) surface are studied by employing spin-polarized density function theory calculations. The surface energy calculation results show that the TaC (0001) terminating with Ta is the most stable surface. According to the optimized structural and energetic properties, it is found that NH₃ prefers to adsorb on the top site, whereas NH₂, H prefer to adsorb on the triple hcp site and NH, N prefer to stay on the triple fcc site. In addition, three transition states are found for analyzing the mechanism of dehydrogenation of NH₃, and the N recombination reaction is also considered. The results show that the desorption of nitrogen atoms is the rate-determining step in the overall reaction. Finally, in order to further elucidate the mechanism of NH₃ adsorption and dissociation on the surface of Ta-TaC, the electronic structure of the most stable adsorption position is analyzed from the perspective of charge density distribution and electron density of states. The results of electronic structure calculation show that NH₃ molecule is adsorbed on the surface through the mixture of 2p<i>_z</i> orbital of N atom and <inline-formula><tex-math id="Z-20211229103116-1">\begin{document}$ 5{\rm d}_{z^2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.png"/></alternatives></inline-formula> orbital of substrate Ta. With the progress of dehydrogenation, the charge transfer phenomenon becomes more and more serious. The charge transfer between adsorbate and substrate plays an important role in accelerating NH₃ dehydrogenation catalytic process.