氢原子在Pt及Pt系双金属催化表面吸附的密度泛函理论研究

采用密度泛函理论(dFT)考察了Pt(100)、(110)、(111)三种表面氢原子的吸附行为, 计算了覆盖度为0.25 ML时氢原子在Pt 三种表面和M-Pt(111)双金属(M=Al, Fe, Co, Ni, Cu, Pd)上的最稳定吸附位、表面能以及吸附前后金属表面原子层间弛豫情况. 分析了氢原子在不同双金属表面吸附前后的局域态密度变化以及双金属表面d 带中心偏离费米能级的程度并与氢吸附能进行了关联. 计算结果表明, 在Pt(100), Pt(110)和Pt(111)表面, 氢原子的稳定吸附位分别为桥位、短桥位和fcc 穴位. 三种表面中以Pt(111)的表面能最低, 结构最稳定. 氢原子在不同M-Pt(111)双金属表面上的最稳定吸附位均为fcc 穴位, 其中在Ni-Pt 双金属表面的吸附能最低, Co-Pt 次之. 表明氢原子在Ni-Pt 和Co-Pt 双金属表面的吸附最稳定. 通过对氢原子在M-Pt(111)双金属表面吸附前后的局域态密度变化的分析, 验证了氢原子吸附能计算结果的准确性. 掺杂金属Ni、Co、Fe 的3d-Pt(111)双金属表面在吸附氢原子后发生弛豫, 第一层和第二层金属原子均不同程度地向外膨胀. 此外, 3d金属的掺入使得其对应的M-Pt(111)双金属表面d带中心与Pt 相比更靠近费米能级, 吸附氢原子能力增强, 表明3d-Pt系双金属表面有可能比Pt具有更好的脱氢活性.

Study of Hydrogen Adsorption on Pt and Pt-Based Bimetallic Surfaces by Density Functional Theory

The surface energies and surface relaxation of Pt(100), (110), and (111) surfaces, as well as the hydrogen adsorption behavior on three Pt surfaces and M-Pt(111) (M=Al, Fe, Co, Ni, Cu, Pd) bimetallic surfaces with a coverage of 0.25 ML were calculated by density functional theory (DFT). The most favorable adsorption sites, adsorption energies, and relaxation during adsorption were obtained. The hydrogen local density of states before and after the adsorption, the positions of the d-band center of different bimetallic surfaces with respect to the Fermi level were analyzed and further related to hydrogen adsorption energies. The calculations showed that the easiest adsorption sites of hydrogen on Pt(100), Pt (110), and Pt(111) are, in order, the bridge site, the short bridge site, and the fcc hollow site. The Pt(111) surface has the lowest surface energy among the three Pt surfaces and the Pt(111) surface is the most stable structure. However, the fcc hollow site is the most stable adsorption site for different M-Pt(111) bimetallic surfaces. The Ni-Pt bimetallic surface showed the lowest hydrogen adsorption energy among the M-Pt(111) bimetallic surfaces. The Co-Pt bimetallic surface showed the next lowest hydrogen adsorption energy, indicating that hydrogen adsorption on Ni-Pt and Co-Pt bimetallic surfaces is more stable. In addition, the first layer and the second layer have an expanding tendency with some degree after hydrogen adsorption on Ni-Pt, Co-Pt, and Fe-Pt bimetallic surfaces. The addition of a 3d metal surface layer on Pt(111) was found to move the d-band center closer to the Fermi level when compared with the bulk Pt metal, and increases the hydrogen adsorption ability by means of the density of state analysis of the bimetallic surfaces model. This reveals that 3d-Pt bimetallic surfaces are likely to have better dehydrogenation activity than Pt.