NH_x(x=1～3)在金属Ir表面吸附与解离的第一性原理研究

采用密度泛函理论,在slab模型下,研究了NH_x(x=1~3)在Ir(100)、Ir(111)和Ir(110)表面上的最稳定吸附位置、几何构型以及逐步脱氢分解过程,计算了相应的吸附能和活化能.计算结果表明,在Ir(100)、Ir(111)面上,NH_3是以C_3轴垂直吸附在顶位,在Ir(110)上,NH_3是以N-Ir键与表面成68.6°吸附在顶位,且吸附能依赖于表面的结构而不同,相比而言,NH_3更容易吸附在开放表面Ir(100)、Ir(110)面上,说明NH_3在这些表面的吸附具有结构敏感性.NH_(x(x=1~3))的分解,在Ir(100),NH_3的吸附与分解存在竞争,在Ir(110)面NH_3最容易分解,在Ir(111)面NH_3是分子性吸附,不能分解.NH_2、NH在三个表面均能够分解,在Ir(110)面活化能均较高.

First-principle Study on NHx(x=1~3) Adsorption and Dissociation on Ir Surface

The most stable adsorption position, geometry structure and gradual dehydrogenation NHx(x=1~3) on Ir (100), Ir (111) and Ir (110) surfaces have been investigated using density functional theory in slab model. The corresponding adsorption energy and activation energy were calculated. The results show that NH3 is found to be perpendicular to top position as C3 axis on Ir (100), Ir (111) surfaces, on Ir (110) , NH3 prefers the top site with inclining 68.6 of N-Ir bond relative to the surface, and the difference of adsorption energy depends on the diversity of the surface structure, NH3 is found to be more easily absorbed on open surfaces of Ir (100), Ir (110) . NH2 adsorbed on bridge site on three surfaces, on Ir (100), (111) surfaces NH favor hollow location, NH prefers short bridge site on Ir (110) surface, the adsorption energy decreased with the H atoms increasing .To the decomposition of NHx, on Ir(100), the adsorption and decomposition of NH3 is competitive, on Ir (110) NH3 dehydrogenation is easy to occur, NH3 is molecular adsorption on Ir (111), not decomposition. NH2, NH on the three surfaces can be decomposed, on Ir (110), the activation energies of H depletion for NH2, NH are higher. The above consequences could adequately indicate that the adsorption and dehydrogenation of NHx on Ir surfaces is structure sensitive.